Regents Chemistry

A topic-by-topic review using the entire January, 2012 Chemistry Regents Exam.
  • Lectures 88
  • Video 2 Hours
  • Skill level all level
  • Languages English
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Course Description

This course offers a topic-by-topic overview of the concepts taught in a high school Regents Chemistry class.

(Click HERE to get the FREE Review Sheet for "100 Ways to Pass the Chemistry Regents!")

Using all 85 questions from the January, 2012 Chemistry Regents, videos are used to demonstrate how to answer each multiple choice and short answer question.

Each video also offers additional information, such as why other answers are incorrect or common mistakes students make.

Many videos describe how to use the Chemistry Reference Tables properly.

What are the requirements?

  • The 2011 Edition of the Physical Setting/Chemistry Reference Tables

What am I going to get from this course?

  • Over 88 lectures and 2 hours of content!
  • By the end of each SECTION, you should be able to fare well on an exam based on the unit covered.
  • By the end of the COURSE, you will be in a good position to score well on the Chemistry Regents.

What is the target audience?

  • This course is intended for high school students in the state of New York who are taking a Regents Chemistry class.

What you get with this course?

Not for you? No problem.
30 day money back guarantee

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Certificate of completion

Curriculum

Section 1: Introduction
What to expect from "Regents Chemistry"!
Preview
01:18
Terms of Use
Preview
00:24
Section 2: Matter
01:26

Question # 20 from the January, 2012 Chemistry Regents

(See also Way # 2 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are matter and substance.

Matter is made up of substances such as elements and compounds.

Some examples of elements include nitrogen, hydrogen, oxygen, sodium, chlorine and calcium, just to name a few.

Elements chemically combine to form compounds, such as water, salt, carbon dioxide and ammonia.

Matter can also consist of mixtures, which is when elements and/or compounds physically combine.

A mixture can be a combination of elements, a combination of compounds or a combination of elements and compounds.

Since air consists mainly of nitrogen and oxygen, as well as carbon dioxide, it is classified as a mixture and therefore incorrect.

Milk has protein and fat compounds in it as well as good old calcium, making this choice a mixture.

Seawater is incorrect because the ocean has water, salt and oxygen for the fish.

Ammonia, which could be used as a cleaning agent, has the formula NH3, which is a single substance, making choice 2 correct.

00:49

Question # 18 from the January, 2012 Chemistry Regents

(See also Way # 4 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are chemical change.

A chemical change is a change which creates a new substance. Let’s see how this works.

When alcohol evaporates, all it is doing is changing from a liquid to a gas, but it is still alcohol.

When water vapor forms snowflakes, all it is doing is changing from a gas to a solid, but it is still water.

When NaCl is crushed into powder, all it is doing is changing from big pieces to smaller pieces.

When glucose reacts with oxygen, it produces two new substances, carbon dioxide and water, making choice 4 the correct answer.

01:17

Question # 72 from the January, 2012 Chemistry Regents

(See also Way # 5 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is substance.

A substance can either be an element, which can be identified by a single capital letter.

Or a compound, which will have a minimum of 2 capital letters to show that the elements have been chemically combined.

Therefore, compounds can be broken down chemically where as elements can not.

So we need to find something in the passage that can not be broken down by a chemical change, or in other words, an element.

The passage mentions iron, air and water.

Iron is an element and therefore the answer.

Water is a compound.

Air is incorrect because it is a mixture which is a physical combination of elements and/or compounds.

Alternatively, you can always consult Table S of the chemistry reference table which lists the elements by name, symbol as well as many of their properties.

00:45

Question # 73 from the January, 2012 Chemistry Regents

(See also Way # 4 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are chemical property.

A chemical property describes how a substance behaves in a reaction.

Using equation 1, iron, whose symbol is Fe, reacts with oxygen to form a compound.

Metals, such as iron, have a tendency to lose electrons when reacting.

When metals lose electrons, they form positive ions.

So, anyone of these answers would be acceptable chemical properties of iron.

00:58

Question # 10 from the January, 2012 Chemistry Regents

(See also Way # 7 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are in the same phase.

Choices 1 and 4 are automatically eliminated because the phases are different.

We can eliminate choice 3 because H2 and Hg represent 2 different elements so their structures are definitely going to be different and therefore, so will their properties.

Choice 2 is the answer and it represents something called an allotrope.

O2, which is pure oxygen and O3, which is ozone, as in the ozone layer, are allotropes of each other.

An allotrope is an element that can exist in 2 or more forms in the same phase.

These forms will have different structures and therefore different properties.

01:05

Question # 71 from the January, 2012 Chemistry Regents

(See also Way # 2 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are homogeneous mixture.

In a homogeneous mixture, the particles are evenly distributed, like in salt water.

The salt is dissolved throughout the water so while you can’t see, it’s in there.

To show that the particles in a homogeneous mixture are evenly distributed, we can take a sample from the top, middle, and bottom and see that they are all the same.

As opposed to a heterogeneous mixture, where the particles are not evenly distributed, for example, oil and water.

If samples from here are also taken from the top, middle and bottom, they will not be same.

So, you should know that all solutions are homogeneous mixtures and that the particles are evenly distributed.

01:06

Question # 23 from the January, 2012 Chemistry Regents

The keywords in this question are separated by filtration.

Since sand and salt are both made up of very tiny particles, even the tiniest of filters, such as filter paper, may not be effective in separating the two from each other.

Unless, we add water. The salt will dissolve in the water, allowing it to pass through the filter paper with the water, leaving the sand behind.

Since the sand did not dissolve in the water, we say it is insoluble.

Salt, on the other hand, did dissolve, so we say that it is soluble.

Therefore, sand and salt differ in their solubility in water, allowing them to be separated by filtration.

Heating up the water will get it to evaporate or boil out, leaving behind the salt.

Section 3: Solid, Liquid, Gas
01:00

Question # 15 from the January, 2012 Chemistry Regents

The keywords in this question are definite shape and definite volume.

Let’s start with choice 2, the gas phase.  The particles of a gas are far apart and tend to move around quickly allowing the gas to have no definite shape and no definite volume.

Choice 3, the liquid phase, has its particles closer together and moving slower, allowing the liquid to take the shape of its container yet still has a set volume.

For choice 4, the solid phase, the particles are tightly packed and vibrate slowly in place, allowing the solid to have a definite shape and a definite volume, making this the correct answer.

aq, which stands for aqueous, means something is dissolved in water.

For the sake of this question, let’s just say that it is similar to the liquid phase, making
this choice incorrect as well.

01:27

Question # 41 from the January, 2012 Chemistry Regents

(See also Way # 10 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are an increase in disorder.

Sometimes, the word entropy may be used instead of disorder, and it typically refers to the way the particles of a substance are arranged.

So all we really need to focus on here are the phases, or the letters in parentheses.

The s in parentheses stands for the solid phase, whose particles are very neat and orderly.

The l in parentheses stands for the liquid phase, whose particles are more loosely packed, giving them the ability to flow.

The g in parentheses stands for the gas phase, whose particle's are all over the place and tend to move around rapidly.

So, solids have the least amount of disorder or the lowest entropy, and the entropy increases with each change in phase, with gases having the greatest entropy or disorder.

If we apply this information to the 4 choices, choice 1 goes from a solid to a gas, which is an increase in disorder, making this answer correct.

Choice 2 is incorrect because it goes from a gas to a solid, which is a decrease in disorder.

Choice 3 is also incorrect. The main change here is from a gas to a solid.

Choice 4 is also incorrect because it changes from a gas to a liquid.

01:00

Question # 38 from the January, 2012 Chemistry Regents

(See also Way # 12 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are vapor pressure.

We want to turn to Table H of the chemistry reference table which is called “Vapor Pressure of Four Liquids.”

The liquid we need to focus on is ethanol which is the 2nd line from the left.

According to the question, the vapor pressure of ethanol is at 80kpa, which is somewhere around this area of Table H.

Let’s enlarge this section so you can see that the scale goes up by 10’s.

This would put 80kpa exactly 2 lines below 100.

Follow that line across until you reach the curved line for ethanol.

From that point go straight down and you will reach the temperature.

The temperature looks like it’s just under 75 degrees making the answer choice 2, 73 degrees C.

01:07

Question # 19 from the January, 2012 Chemistry Regents

(See also Way # 8 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are kinetic molecular theory.

The kinetic molecular theory describes how the particles of an ideal gas behave.

As you can see in the picture, gas particles move in a random, constant straight line motion, making the answer choice 2.

Choice 1 is wrong because solids, not gases, are arranged in a regular geometric pattern.

Gas particles move at a high rate of speed allowing them to have little to no attraction between particles, making choice 4 incorrect.

The gas particles may collide with each other or the walls of the container but no energy will be lost.

Finally, the volume of a gas particle is so small compared to the volume of its container, we say that it barely takes up space and can be far apart from other gas particles, making choice 3 incorrect.

01:50

Question # 17 from the January, 2012 Chemistry Regents

(See also Way # 11 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are identical sealed cylinder, so let’s draw 2 identical, sealed cylinders.

Another keyword, or letters in this case, are STP.

STP stands for standard temperature and pressure, values for which can be found on Table A of the chemistry reference table.

Since the cylinders are identical and both are at STP, they will have the same volume, which is 1 liter, the same temperature, we’ll use 273 kelvin, and we’ll use 1 atm or atmosphere for both pressures.

This brings us to Avogadro’s hypothesis.

Avogadro’s hypothesis states that at the same volume, temperature, and pressure, two different gases will have the same number of particles.

The word particles could mean molecules if we are referring to compounds, which we aren’t, or atoms, if we are referring to elements, like we are in this case.

He and Ne are both elements so the answer will be choice 1, atoms.

To help further illustrate avogadro’s hypothesis, let’s say we have 3 atoms of Helium in one cylinder. How many atoms of Neon would there need to be in the other cylinder
which is at the same volume, temperature, and pressure?

If you guessed 3, you would be correct!

01:42

Question # 39 from the January, 2012 Chemistry Regents

The keywords in this question are volume, pressure and temperature.

The combined gas law, a formula found on Table T of the chemistry reference table, involves all 3 terms.

However, since the temperature of the gas starts at 25 C and is held at 25C, we don’t need to include it in the formula. We say that the temperature remained constant.

What is the new pressure means that we need to solve for P2.

To get P2 alone, we need to divide V2 from both sides or simply move V2 to the bottom of the other side.

P1, or the initial pressure, is 125 kPa.

V1, or the initial volume, is 145 mL.

The final volume, or V2, is 80.ml

When you multiply 125 by 145 you should get 18125 as the numerator.

Divide that by 80 and P2 will equal 226.5625 kpa.

The closest answer is choice 4 which is really nothing more than rounding 226 to the
nearest ten.

Section 4: Heat
00:35

Question # 56 from the January, 2012 Chemistry Regents

(See also Way # 13 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are average kinetic energy.

The word temperature is a measure of the average kinetic energy of the particles of a sample.

So we can replace the words average kinetic energy with the word temperature.

Therefore, the particles of this sample have the lowest temperature at the 16 minute mark.

01:29

Question # 55 from the January, 2012 Chemistry Regents

The keywords in this question are melting point.

The melting point is the temperature at which a solid begins to turn into a liquid.

According to the passage, this substance started out as a gas at 206 degrees Celsius.

As the substance is allowed to cool, it changes from a gas to a liquid during this segment of the graph in a process known as condensation.

Then the substance will be entirely in the liquid phase during this segment.

Followed by another phase change from liquid to solid during this segment, in a process known as freezing.

Finally, with continued cooling, the substance will be completely in the solid phase during this segment of the graph.

If this were a heating curve, the same thing would happen, just in the reverse order, but instead of freezing, melting would occur and instead of condensing, boiling would occur.

In essence, the freezing point and melting point occur at the same temperature, which in this case is 90 degrees Celsius, making this the answer to the question.

If the question asked about the boiling point or condensing point, the answer would have been 150 degrees Celsius.

01:45

Question # 57 from the January, 2012 Chemistry Regents

The keywords in this question are particle diagrams.

According to the key in the answer booklet, a single, unshaded circle represents a particle of the substance.

Using the boxes provided in our answer booklet, we need to draw particle diagrams that represent the two phases of the sample at minute 4.

According to the passage, this substance started out as a gas at 206 degrees Celsius.

As the substance is allowed to cool, it changes from a gas to a liquid during this segment of the graph.

Then the substance will be entirely in the liquid phase during this segment.

Followed by another phase change from liquid to solid during this segment.

Finally, with continued cooling, the substance will be completely in the solid phase during this segment of the graph.

During minute 4, the two phases present are gas and liquid.

So in the first box, we can draw the particles far apart from each other just like they are in the gas phase, making sure to include at least 6 particles for each diagram.

In the other box, we will draw at least six particles loosely packed together like that of a liquid.

Had the question asked about the solid phase, like around minute 15, the particle diagram would have had the particles arranged very tightly packed.

Section 5: Atom
01:03

Question # 3 from the January, 2012 Chemistry Regents

The keywords in this question are gold foil experiment.

In 1909, a scientist by the name of Ernest Rutherford shot radioactive alpha particles at a thin sheet of gold foil.

Rutherford put a screen around the foil so that anytime an invisible alpha particle touched it, it would create a spark.

One of the observations Rutherford made was that most of the alpha particles went straight through the gold foil.

Based on this observation, he concluded that an atom consists of mostly empty space.

Occasionally, though, it appeared that some of the alpha particles got deflected, or rerouted.

Based on this observation, Rutherford concluded that atoms must have had something small, yet dense inside of it to cause the alpha particle to change its direction, making the answer, choice 2.

00:47

Question # 25 from the January, 2012 Chemistry Regents

(See also Way # 18 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is orbital.

Very simply put, an orbital is the most probable location of finding an electron, making the answer, choice 4.

The wave-mechanical model is the most current explanation we have today as to the whereabouts of electrons.

The animation on the left is cycling through the different orbitals of the first three energy levels of an atom. While we know electrons surround the nucleus of an atom, they are constantly moving. So, depending on which energy level an electron is in, there is a good probability of knowing where it is based on its orbital.

00:36

Question # 4 from the January, 2012 Chemistry Regents

(See also Way # 19 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is atom.

An atom consists of a nucleus, which houses positively charged protons and neutral neutrons.

So, overall, the nucleus will be positively charged, eliminating choices 1 and 2.

Electrons, which are negatively charged, surround the nucleus.

Therefore, the correct answer is choice 3.

00:39

Question # 6 from the January, 2012 Chemistry Regents

(See also Way # 21 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is particle, whose symbols can be found on Table O of the Chemistry Reference Table.

The number on top of the notation for the symbol represents the mass number, so an alpha particle has a mass of 4.

A beta particle, or an electron, has a mass of 0. A neutron has a mass of 1 and a proton also has a mass of 1.

So the particle with the least mass is choice 2, the beta particle.

00:58

Question # 2 from the January, 2012 Chemistry Regents

(See also Way # 22 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are number of electrons in an atom.

First of all, all atoms are electrically neutral.

What this means is that all the charged particles that make up an atom will ultimately cancel each other out.

The 3 particles that make up an atom are the p, e, and n.

The p stands for protons which have a + charge.

The e stands for electrons which have a – charge.

The n stands for neutrons which have no charge, so when you add everything up
you get a net charge of 0, or neutral.

Since we know there are 3 protons, and neutrons are neutral, so they don’t really matter, we can easily figure out how many electrons there must be to make the atom electrically neutral.

00:55

Question # 1 from the January, 2012 Chemistry Regents

The keywords in this question are completely filled second shell.

All atoms consist of a nucleus with differing numbers of protons and neutrons.

The electrons, which also differ in number from atom to atom, surround the nucleus in several different energy levels, or shells.

Although there are 7 known shells, we’ll just concern ourselves with the first 4.

Each energy level can only hold a certain number of electrons in what we’ll call their maximum capacities.

The 1st energy level can only hold 2 electrons, the 2nd 8, the 3rd 18 and the 4th 32.

Since the question asked about the 2nd shell, it will be completely filled when it holds a total of 8 electrons.

01:11

Question # 5 from the January, 2012 Chemistry Regents

The keywords in this question are outermost electron with the most energy.

All atoms consist of a nucleus with differing numbers of protons and neutrons.

The electrons, which also differ in number from atom to atom, surround the nucleus in 7 different energy levels.

The energy level closest to the nucleus has the least amount of energy and the one that is furthest away has the most.

So, if we look up the elements listed here, in the periodic table of elements, we can see which element has the most energy using 2 methods.

First, we can look at each element’s electron configuration and count to see how many energy levels its electrons occupy.

Or, even easier, the period number the element is in tells you exactly how many energy levels its electron’s occupy.

Since cesium is in period 6, its electrons occupy 6 energy levels, giving its outermost electrons have the most energy.

00:33

Question # 31 from the January, 2012 Chemistry Regents

(See also Way # 36 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are valence electrons.

Valence electrons are the electrons in the outermost energy level.

So if we turn to the Period Table of Elements and look at germanium, we see that it has an electron configuration of 2-8-18-4, with 2 being in the inner most energy level and 4 being the outermost energy level, making the answer choice 4, 4.

01:49

Question # 32 from the January, 2012 Chemistry Regents

(See also Way # 25 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are excited state electron configuration.

First, we should point out that the electron configurations listed in the periodic table of elements are in the ground state. The ground state is when the elements’ electrons are in their lowest levels.

If we look at an atom, the electrons surround the nucleus in various energy levels with the innermost level having the least amount of energy and the outermost energy level having the most energy.

Since choice 1 has calcium having 2 electrons in the 1st energy level, 8 in the 2nd, 8 in the 3rd and 2 in the 4th, just like it says in the periodic table, then this is considered to be the ground state for calcium.

The excited state would be if an electron from an inner energy level gains enough energy to “jump” to an outer energy level of higher energy. We say it got excited. So, instead of 2-8-8-2, the excited state for calcium would be 2-8-7-3, without changing the total number of electrons. Therefore choice 1 is incorrect.

Choice 2 is incorrect because 2-8-1 is the ground state for Na.

Rather than jumping to a higher level, an electron was added instead, changing the total number of electrons, which is not the excited state.

The same thing happened to F in choice 4.

That makes choice 3 the answer and it is correct because 2 electrons jumped from the 2nd energy level to the 4th energy level, becoming excited, without changing the total number of electrons.

01:06

Question # 69 from the January, 2012 Chemistry Regents

(See also Way # 26 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are subatomic particles and energy states.

If we look at an atom, the electrons surround the nucleus in various energy levels with the innermost level having the least amount of energy and the outermost energy level having the most energy.

The ground state is when the electrons are in their lowest levels, like in this picture.

During a fireworks display, salts are heated to very high temperatures.

The salts absorb energy and become excited, or enter the excited state, when electrons jump to higher energy levels.

However, energy is emitted from the ions in the form of light, when the electrons, move from high energy states, back down to lower energy states.

01:04

Question # 35 from the January, 2012 Chemistry Regents

The keywords in this question are ion and net charge.

An ion is an atom with an excess charge; which can be extra positive or extra negative.

The net charge is calculated by adding up the charges of all the particles in the atom.

The 3 particles that make up an atom are the p, e, and n.

The p stands for protons which have a + charge.

The e stands for electrons which have a – charge.

The n stands for neutrons which have no charge, so when you add everything up you get the net charge.

Since we know there are 7 protons, 10 electrons and neutrons are neutral, so they don’t really matter, we can just add the protons and electrons to get the net charge of -3 or 3-, making the answer choice 2.

01:25

Question # 53 from the January, 2012 Chemistry Regents

The keyword in this question is particle.

Table O of the chemistry reference tables has a list of particles that a fluorine atom could have gained
to become a fluorine ion.

Since the fluorine atom became a negative ion, it had to have gained a beta particle, also known as an electron, which is the only negatively charged particle found in Table O.

To fully understand how this happens, let’s look at a fluorine atom.

Fluorine, with an atomic number of 9, has 9 positively charged protons and 9 negatively charged electrons, which cancel each other out to make the atom electrically neutral.

When it gains 1 electron, it becomes a fluorine ion which still has 9 positively charged protons but now
has 10 negatively charged electrons, giving the ion a negative one charge.

This is the same number than can be found in the upper right hand corner of fluorine’s box, known as an oxidation state, which tells us how many electrons an atom can lose or gain.

Section 6: Nuclear
01:02

Question # 9 from the January, 2012 Chemistry Regents

The keyword in this question is Cs 137 over 55.

Anytime an element is written with its symbol and a number written above it to the left that is its mass number.

The number written below the symbol to the left is its atomic number.

This would make the answer, choice 3.

Alternatively, this nuclide could be written as Cs-137 or cesium -137.

The reason why the 137 is important is because, in addition to cesium 137, there could be other forms of cesium
known as isotopes, such as cesium 135 and cesium 136.

What makes these isotopes is that they have the same atomic number but a different mass number.

00:48

Question # 83 from the January, 2012 Chemistry Regents

The keywords in this question are penetrating power.

Penetrating power describes the ability of radiation to travel through a substance.

Cobalt 60 emits 2 types of radiation: gamma rays and beta particles.

Gamma rays travel at the speed of light making them very powerful forms of radiation.

Beta particles travel at slower speeds making them less powerful.

So, to answer the question, gamma radiation has greater penetrating power or just as acceptable, beta particles have weaker penetrating power.

00:37

Question # 82 from the January, 2012 Chemistry Regents

(See also Way # 33 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are one risk to human tissue.

The first few words of the first paragraph pretty much would be considered an acceptable answer.

Ironically, while exposure to radiation may kill cancer cells, radiation can also cause gene mutations which can lead to cancer.

Nausea, or other health issues, are just as acceptable.

01:59

Question # 49 from the January, 2012 Chemistry Regents

(See also Way # 30 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are nuclear reaction.

One of the most famous people who helped discover and understand nuclear chemistry was Albert Einstein.

Einstein developed the equation E = mc squared, where E stands for an enormous amount of energy, m stands for mass and c stands for the speed of light squared.

What this meant was that if we can get a small, tiny piece of mass to travel at such a high rate of speed, that mass can be converted to a huge amount of energy.

Therefore, we can eliminate choices 2 and 4 since mass gets converted to energy and not the other
way around.

Fission involves the splitting of an atom.

In fission, a heavy nucleus, such as uranium, gets bombarded by a high energy particle, such as a neutron, causing it to split, or break apart into smaller nuclei, in this case, represented by barium and krypton.

The extra, small pieces of mass, in this case 3 neutrons, are what gets converted to energy.

Choice 1 is incorrect, since fission involves uranium and the reaction in this question does not include
uranium.

Fusion is when two nuclei unite to form a heavier nucleus.

A hydrogen 2 nucleus, represented by this dot will unite with a hydrogen 3 nucleus, represented by this dot, to form a heavier nucleus represented by helium.

The extra, small piece of mass, in this case a neutron, is what gets converted to energy, making choice 3
the answer.

01:29

Question # 84 from the January, 2012 Chemistry Regents

The keywords in this question are beta decay.

The answer booklet has the following incomplete equation which shows how cobalt-60 emits or gives off a beta particle.

Our job is to complete the nuclear equation by writing an isotopic notation for the missing product.

This is done by following the law of conservation of mass where the mass before must equal the mass after.

So, 60 = 0 + what?

60 = 0 + 60 making the top number 60

The same thing should happen on the bottom except this is called the law of conservation of charge where the charge before must equal the charge after.

So, 27 = -1 + what?

27 = -1 + 28 making the bottom number 28.

Since 27 is the atomic number for cobalt, but the bottom number is no longer 27, we need to write the new symbol for the element having atomic number 28, or Ni for nickel.

Everything written in the red box represents the answer to this question.

01:27

Question # 85 from the January, 2012 Chemistry Regents

The keywords in this question are total time elapsed.

In other words, how long did it take for cobalt-60 to decay and most likely involves a half-life calculation.

Half-life means the amount of time needed to get half as much.

Table N of the chemistry reference table lists the half life for cobalt-60 as 5.271y for years.

Here’s how this works: if we start out with 100 grams of cobalt 60 like the passage says, it will take 5.271 years for the 100 grams to become 50 grams or half as much.

If this now 50 gram sample continues to decay, it would take another 5.271 years for it to be half as much, or 25 grams.

After another 5.271 years go by, 12.5 grams of cobalt-60 would remain unchanged and that is where the question says to stop.

So, after 3 half life periods of 5.271 years, the total time elapsed would be equal to 15.813 years.

Section 7: Periodic Table
01:21

Question # 11 from the January, 2012 Chemistry Regents

(See also Way # 34 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are periodic table, so let’s take a look at the periodic table of elements found in the chemistry reference table.

Rather than look at the whole table, we can zoom into a section of the table and use the key to help us find the answer.

If you look at the key, the atomic mass of an element can be found in the upper left corner of the box.

At first glance, it looks like the atomic masses are going up, but in some cases, like here, the mass drops down, making this answer incorrect.

The 2nd answer, atomic number, which is the bold number in the lower left corner of the box, is the correct answer because, as you can see, the atomic numbers are increasing across the whole entire row without any disruptions.

Choice 3 is wrong because molar mass is not listed in the key and therefore isn’t found on the periodic table.

The 4th choice, oxidation number, while listed in the key, is incorrect. The oxidation states start to increase, but then they go down and some elements even have more than one oxidation state.

00:41

Question # 7 from the January, 2012 Chemistry Regents

(See also Way # 37 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are Group 2.

Group 2 can be found on the periodic table of elements.

We can eliminate choice 4 because the noble gases can be found in group 18.

The elements in this circle represent the metalloids, eliminating choice 2.

Metalloids, which have metallic and non-metallic properties, separate the metals to the left from the nonmetals on the right.

Since group 2 is to the left of the metalloids, we can eliminate choice 3 making choice 1, metals, the answer.

01:01

Question # 8 from the January, 2012 Chemistry Regents

(See also Way # 38 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are most similar chemical properties.

Elements in the same group have similar properties.

So let’s take a look at the Periodic Table of Elements in the chemistry reference table.

The elements listed in the 1st set of answers are not in the same group, making choice 1 incorrect.

The same thing can be said for the 2nd set of answers, making this choice incorrect.

While the 4th set of answers are next to each other, they are in the same period, not the same group, making choice 4 incorrect.

The 3rd set of answers ARE located in the same group and therefore have the most similar chemical properties.

The reason why elements in the same group have similar properties is because they have the same number of valence electrons.

All of the elements in Group 16 have 6 valence electrons.

00:59

Question # 21 from the January, 2012 Chemistry Regents

(See also Way # 40 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is electronegativity.

Electronegativity means attraction for electrons and is measured on a scale of 0.0 to 4.0 where 4.0 is the highest and strongest.

The electronegativity values for elements can be found on Table S of the chemistry reference table.

F is fluorine which has an electronegativity of 4.0.

Choice 1 is automatically wrong because 4.0 is the highest and we want the lowest.

Fr, or francium has an electronegativity of 0.7, so this could be the answer but let’s check the last 2 elements and their electronegativity values just to be sure.

Clearly, Fr has the lowest electronegativity value.

00:49

Question # 54 from the January, 2012 Chemistry Regents

(See also Way # 42 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are first ionization energy.

First ionization energy is the amount of energy needed to remove the outermost electron from an atom.

Table S of the chemistry reference table has the values for each element’s ionization energy.

If we look up the elements in group 1, which are lithium, sodium, potassium and rubidium, we can see that as the atomic number goes increases, the first ionization energy decreases.

01:45

Question # 52 from the January, 2012 Chemistry Regents

(See also Way # 39 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is radius.

The nucleus of an atom is surrounded by energy levels or electron shells.

Since this question deals with sodium and potassium, let’s look them up in the periodic table of elements.

The period number actually tells you how many electron shells the electrons occupy for the elements in that period.

So, sodium, with an electron configuration of 2 8 1, has 2 electrons in the first energy level, 8 in the 2nd and 1 in the 3rd.

The radius, which is measured in picometers, or pm, is the distance from the nucleus to the outermost electron shell.

Potassium, which has an electron configuration of 2, 8, 8, 1, or 2 in the 1st, 8 in the 2nd,
8 in the 3rd and 1 in the fourth.

The radius for a potassium atom is larger than sodium’s because it extends out by one extra electron shell.

For this same reason, a potassium ion has more electron shells than a sodium ion.

The only difference is that when sodium and potassium become ions, they both lose their outermost electrons causing their atomic radii to become smaller ionic radii but potassium will still have one more electron shell than sodium.

00:48

Question # 51 from the January, 2012 Chemistry Regents

The keyword in this question is estimate.

When estimating, your answer can really be any number for the radius of a bromine ion.

But if you look carefully at the chart, the radii are increasing beginning with 133 picometers for the fluorine ion, 181 picometers for the chlorine ion, we’re not sure about the bromine ion and 220 picometers for the Iodine ion.

Therefore, we can estimate the radius of a bromine ion to be any number greater than 181 picometers and less than 220 picometers.

Section 8: Bonding
01:02

Question # 16 from the January, 2012 Chemistry Regents

(See also Way # 43 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are break the bond.

First, let’s eliminate choices 3 and 4 due to the law of conservation of energy.

This law states that energy cannot be created or destroyed; it can only change from one form to another.

For example, heat energy can be converted into potential energy, or stored energy.

As in the case with Cl2. This is just 2 chlorine atoms held together with a bond.

In order to break the bond, heat energy needs to be absorbed.

After doing so, that heat energy gets converted to potential energy and stored by two separate chlorine atoms.

So, when a bond is broken, energy is absorbed, making the answer choice 1.

The opposite is also true: when a bond is formed, energy is released.

01:22

Question # 13 from the January, 2012 Chemistry Regents

(See also Way # 49 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are stable valence electron configuration.

In chemistry, there is something known as a stable octet.

A stable octet refers to atoms that are most stable when they have 8 valence or outermost electrons, typically when bonding.

Let’s see how many valence electrons each of these elements have.

Neon and radon both have 8 valence electrons and that’s before bonding. Since they already have stable octets, they are most likely not going to react or bond with other elements, making choices 1 and 2 incorrect.

While helium does not have a stable octet, it does have a stable duet.

It is good to know that in an atom, the 1st energy level surrounding the nucleus has a maximum capacity of 2 electrons.

Since helium’s valence electrons are filled to capacity, it too, is considered stable and unreactive, and therefore, incorrect.

Hydrogen is the answer because it will either need to gain 1 electron to become a stable duet or lose its only electron making it stable with none.

01:34

Question # 14 from the January, 2012 Chemistry Regents

(See also Way # 44 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are ionic bond and electrons.

Keep in mind that when bonding, atoms are most stable when they have 8 valence or outermost electrons, something known as a stable octet.

A good example of this is with sodium and chlorine.

For sodium to become a stable octet, it can either lose 1 or gain 7 valence electrons.

For chlorine to become a stable octet, it can either gain 1or lose 7 of its valence electrons.

Both atoms will do what is easiest – sodium will lose its 1 valence electron and become a +1 ion, meanwhile chlorine will gain that 1 valence electron and become a
negative 1 ion. Hence the name, ionic bond.

An ionic bond involves the transfer of electrons from a metal, in this case sodium, to a non-metal, in this chlorine, forming positive and negative ions.

Since electrons are not found in the nucleus, choice 3 is wrong and choice 4 is correct.

Sharing of electrons, as opposed to transferring, implies that both atoms want to gain the electron.


This means that both atoms need to be nonmetals since nonmetals tend to gain
electrons.

Equal sharing means that the nonmetals are most likely the same element where as unequal sharing means the nonmetals are different.

02:27

Question # 28 from the January, 2012 Chemistry Regents

(See also Way # 46 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is carbon.

Carbon is such a versatile element because it as 4 valence electrons and therefore can form up to 4 bonds to form a stable octet or 8 valence electrons.

Due to the infinite number of possibilities of compounds containing carbon, a whole separate subject exists on it called organic chemistry.

Therefore, for this question, we will make use of the 3 chemistry reference tables associated with organic chemistry: Tables P, Q and R.

The question starts off with a molecule called propanal.

“Prop” is actually an organic prefix found in table P which means that this molecule contains 3 carbon atoms.

So in addition to the one carbon atom from before, let’s add 2 more for a total of 3.

As for the bonds, if we go back to the molecule propanal, the “an” comes from the alkane family in Table Q, which simply means that there are single bonds located between carbon atoms like here and here.

The last part of the propanal molecule, the “al” is for an organic functional group found in Table R under the class of compounds called ALdehydes.

In fact, propanal happens to be the same compound used in the example for how to draw an aldehyde.

Like the example, the first carbon has 3 H’s to ensure carbon forms 4 bonds and has a stable octet.

The second carbon has 2 H’s to make sure that this carbon forms 4 bonds and has a stable octet.

With the third carbon, the question says that an oxygen atom is bonded with a carbon atom.

The carbon is actually double-bonded to an atom of oxygen and single bonded to an H completing the four bonds giving it a stable octet.

So, the total number of pairs of electrons shared between carbon and oxygen is 2 pairs, making choice 2 the answer.

01:21

Question # 35 from the January, 2012 Chemistry Regents

(See also Way # 45 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are non polar covalent bond.

A nonpolar covalent bond is a bond between 2 of the same nonmetals.

That would make the answer choice 1 since it is the only choice that has 2 of the same nonmetallic elements bonded together.

It is called nonpolar covalent because they share a pair of electrons equally, resulting in no poles or no charges, hence the name, nonpolar.

Choice 2 contains a polar covalent bond which is a bond between 2 different nonmetals.

It is called polar covalent because they share a pair of electrons unequally, resulting in poles, or weak partial charges.

Choice 4 is wrong because it, too, contains polar covalent bonds.

Choice 3 is also wrong because it contains an ionic bond, which is a bond between a metal and a nonmetal.

It is called ionic because electrons are transferred from the metal to the nonmetal
resulting in positive and negative ions.

01:34

Question # 67 from the January, 2012 Chemistry Regents

(See also Way # 47 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are the two types of chemical bonds.

In general, there are 3 types of bonds: metallic bonds, covalent bonds and ionic bonds.

A metallic bond is a bond between 2 metallic elements.

A covalent bond is a bond between 2 nonmetals.

An ionic bond is a bond between a metal and a non-metal.

According to the passage, the salt used to produce a deep-red color is lithium carbonate, or Li2CO3.

Let’s take a closer look at Li2CO3, along with the periodic table of elements, to see what kinds of elements it has so we can see which 2 types of bonds exist.

The elements touching the black, bold staircase, roughly within this circle are called the metalloids.

The metalloids separate the metals to the left from the nonmetals to the right.

Lithium, which is all the way over here, is a metal.

Meanwhile, carbon and oxygen are both non-metals.

Therefore, the bond between lithium and carbon would be ionic and the bond between carbon and oxygen would be covalent.

02:16

Question # 22 from the January, 2012 Chemistry Regents

(See also Way # 54 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are boiling point.

The boiling point of a substance depends on the strength of the attractive forces between molecules, such as in the two water molecules below, represented by the red
dashed lines.

This is known as an intermolecular force of attraction, where the stronger the force, the higher the boiling point.

So, let’s describe the difference between each type of bonding found in the choices to see which one has the strongest force.

A covalent bond is a bond between 2 nonmetals within a compound, like the line between H and O within a water molecule.

Since this bond is within a molecule of a compound and not between molecules, it is incorrect.

An ionic bond is a bond between a metal and a nonmetal within a compound.

Since this bond also occurs within a compound, it too, is incorrect.

Hydrogen bonding is a bond between hydrogen and the elements nitrogen, oxygen or fluorine between compounds, like in the picture below.

Since the boiling point depends on the force between compounds, choice 3 is most likely the answer.

Choice 4 is incorrect because metallic bonding, as the name suggests, is a bond between elements that are metals and none of the elements mentioned in this question are metals.

The reason why hydrogen bonding only occurs with F, O, N and ultimately produces a stronger force of attraction is because F, O, and N all have small atomic radii and high
electronegativities.

This information can be verified on Table S of the chemistry reference table, where pm stands for pico meters and electrongativity values are based on a scale of 0.0 to 4.0 with 4.0 being the highest.

Section 9: Formula Writing
01:05

Question # 78 from the January, 2012 Chemistry Regents

(See also Way # 55 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are empirical formula.

Empirical means simplest form.

To get a formula into its simplest form, reduce using the greatest common factor.

The paragraph states that ascorbic acid has a molecular formula of C6H8O6.

Let’s write this molecular formula down.

Reduce by dividing the number of C’s, H’s and O’s by the greatest common factor, which in this case, is 2.

6 C’s divided by 2 is 3 C’s, or C3.

8 H’s divided by 2 is 4 H’s or, H4

And 6 O’s divided by 2 is 3 O’s or O3, making the empirical formula C3H4O3.

02:07

Question # 66 from the January, 2012 Chemistry Regents

(See also Way # 58 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are the salt used to produce green light.

The very last line of the passage states that barium chloride is used to produce green light.

Barium chloride is a binary compound meaning that it consists of 2 components, barium and chlorine.

In a binary compound, the 2nd component, in this case, chlorine, will change its ending to IDE.

When writing formulas, we need to look up the oxidation states for the elements, putting the positive oxidation state 1st and the negative oxidation state 2nd. Since chlorine has only one negative oxidation state, that’s the one we have to use.

And just in case you were wondering what if chlorine had more than one negative oxidation state, we typically use the top most oxidation state when dealing with binary compounds.

Oxidation states, by the way, simply tell us how many electrons an atom will lose or gain when reacting in order to obtain a stable octet or 8 valence (outermost) electrons.

Barium will lose the last 2 electrons it has to become a stable octet.

The problem, though, is that chlorine only needs 1 of those electrons to form a stable octet itself.

Since electrons can’t just disappear into thin air, the solution is to bring in another chlorine atom to gain barium’s 2nd electron, making everybody stable.

Therefore, the formula would be BaCl2.

Another, quicker way to get the same formula would be to crisscross the oxidation states, get rid of the signs, and simplify if you can.

The 1 is understood to be there so while you can write the 1, you don’t need to.

02:15

Question # 12 from the January, 2012 Chemistry Regents

(See also Way # 58 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is name.

Don’t let the letters I-U-P-A-C, or IUPAC throw you off.

It simply stands for the International Union of Pure and Applied Chemists, an
organization that came up with rules for naming compounds.

Let’s learn how to write formulas and name compounds.

All of the choices have zinc in them so that’s not the issue.

Since the question asks about the compound ZnO, let’s look at O also, particularly the oxidation states.

Rule 1: the element with the positive oxidation state gets written 1st, negative oxidation state 2nd.

Rule 2: Criss-cross the oxidation states so that they become subscripts, getting rid of the signs.

Rule 3: simplify if you can, so a 2 to 2 ratio becomes a 1 to 1 and you don’t need to write the 1’s.

Since this compound contains just zinc and oxygen, it takes on the name zinc oxide, making the answer choice 1.

To write the formulas for choices 2, 3, and 4, we’ll need to refer to Table E of the chemistry reference table.

On Table E, we see that oxalate has the formula C2O4 with a negative 2 oxidation state.

To write the formula for zinc oxalate, we’ll follow the same rules as before.

Rule 1: the element with the positive oxidation state gets written 1st, negative oxidation state 2nd.

Rule 2: Criss-cross the oxidation states so that they become subscripts, getting rid of the signs.

We use parentheses here to show that we now have 2 oxalates.

Rule 3: simplify if you can, so 2 zincs and 2oxalates becomes 1 zinc to 1 oxalate and you don’t need to write the 1’s.

The formulas for zinc peroxide and zinc hydroxide are written using the same rules as before.

If you follow these rules correctly you should end up with the following formulas.

01:56

Question # 68 from the January, 2012 Chemistry Regents

The keywords in this question are the salt used to produce a bright red color.

According to the passage, strontium carbonate, or SrCO3, produces a bright red color.

Using the period table of elements of the chemistry reference table, let’s take a closer look at the elements found in strontium carbonate, Sr, C and O.

Out of all the information in those boxes, we need to focus our attention on the oxidation states, which are the numbers in the upper right hand corner for each element.

Carbon seems to be the only one listed here with more than one oxidation state.

Our job is to figure out which number is used for carbon in this compound.

In order to do that, we need to know that, in a compound, the sum of the oxidation states must equal zero.

The one caveat here is that we need to take the oxidation state and multiply it by their subscript, in this case 1, equaling 2.

Doing the same thing for carbon, we take the oxidation state and multiply by its subscript, also 1, but since we don’t know which one to use yet, we’ll leave it as a question mark for now.

Repeating this for oxygen, negative 2 times 3 equals a negative six so that when we add all these numbers up we get zero.

So, two plus what plus negative six equals zero?

The answer is positive four, which is carbon’s third oxidation state.

02:00

Question # 33 from the January, 2012 Chemistry Regents

(See also Way # 57 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are types of chemical reactions.

There are 4 general types of reactions.

A synthesis reaction involves 2 or more substances combining to form one, single substance.

Decomposition, which is the exact opposite of synthesis, involves 1 substance breaking down into 2 or more substances. This is the type of reaction occurring in the 2nd reaction.

A single replacement reaction involves one element taking the place of another that is already part of a compound ultimately forming a new compound and a new element.

In this scenario, A is an individual element, B+ represents a metal that is part of a compound and C- represents a nonmetal that is part of the same compound.

Metals tend to lose electrons when bonding and become positive ions; nonmetals tend to gain electrons when bonding and become negative ions.

We write positive first, negative second.

It matters, though, what type of element, element A is.

If element A is a metal, then it may be able to replace metal B, so that AC is the new compound and B is the new element.

Alternatively, if A is a nonmetal, then it may be able to replace nonmetal C, so that BA is the new compound and C is the new element.

This is what happened in the first reaction, therefore making the answer choice 1.

Finally, there are double replacement reactions.

In this type of reaction, the elements from two different compounds switch partners, keeping in mind that we write positive first, negative second.

01:29

Question # 47 from the January, 2012 Chemistry Regents

(See also Way # 91 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are reference table J and react spontaneously.

Let’s first pull up reference Table J.

Table J lists both metals and nonmetals from most active at the top to the least active at the bottom.

In order for a reaction to occur spontaneously, the element that is by itself needs to be more active, or higher on Table J, than the similar type of element in the compound, in this case, metals.

Let’s check to see how this works. Mg, the individual element, is located here in the metals column in table J, meanwhile, Zn, the metal in the compound, is located here.

Since Mg is located higher than Zn on table J, it is a more active metal and therefore will replace Zn in this single replacement reaction, producing MgCl2 plus Zn.

In choice 2, Pb is located below Zn, making it less reactive and therefore, there will be no reaction.

The same is true for choice 3 between Cu and Fe producing no reaction.

As is the case for choice 4 between Co and Na, confirming choice 1 to be the answer.

01:36

Question # 74 from the January, 2012 Chemistry Regents

The keyword in this question is balance.

A balanced equation has the same number of atoms on both sides of the equation.

So for equation 2, we will list the elements and how many atoms they each have on both sides.

On the left side of the equation, there is 1 iron.

For O, there are 3, 2 from O2 and 1 from H2O and for H, there are 2.

On the right side of the equation, there is 1 iron, 2 oxygen’s and 2 hydrogen’s.

Since the right side has fewer O’s than the left side, we’ll adjust this side first to keep the coefficients to the smallest, whole number.

By putting a 2 in front of FeOH2, everything will double: there are now 2 iron’s, there will be 4 oxygen’s and there will be 4 hydrogen’s.

To fix the left side, we’ll need to put a 2 in front of the Fe to make it equal to the right side.

And in order to get 4 oxygen's and 4 hydrogen's on the left side, we’ll need to put a 2 in front of the H20.

The 2 O’s from here and now 2 O’s from here equal 4 O’s total.

Two times 2 H’s also gives us 4 H’s completing the balancing of this equation.

Section 10: Chemistry Math
01:30

Question # 36 from the January, 2012 Chemistry Regents

The keyword in this question is kilojoules.

We can break this word up into 2 parts, kilo and joules.

The prefix kilo, can be found on Table C of the chemistry reference table.

The word joules, can be found on Table D of the chemistry reference table.

The prefixes in Table C are from the metric system which is based on factors of 10.

The prefix kilo has a factor of 10 to the 3rd power, meanwhile a joule, or anything else in Table D for that matter, has no prefix, and therefore will be a factor of 10 to the 0 power.

Now that we have the exponents in place, we can subtract them to find out how many places to move the decimal point and in which direction.

3 minus 0 equals positive 3 which means we will move the decimal point 3 places to the right.

So, if we begin with 50 kilojoules, moving the decimal point 3 places to the right gets us to 50 thousand joules, which eliminates choices 1 and 2.

So while 50 kilojoules equals 50 thousand joules, the correct scientific notation would be choice 4, 5 x 10 to the fourth power, since the decimal point is 4 places removed from the 5.

02:59

Question # 63 from the January, 2012 Chemistry Regents

The keywords in this question are significant figures.

Significant figures, deal with the precision of measurements. 

For example, if we look at a ruler, we know that this arrow is pointing somewhere between 5 and 6.

Halfway between 5 and 6 would be 5.5 so we know the arrow is somewhere between 5 and 5.5.

Halfway between 5 and 5.5 is 5.25, so this arrow is somewhere between 5.25 and 5.5

Basically, we are certain about a part of the measurement but estimating on the rest.

So we have rules for identifying significant figures for any kind of measurement including the volume of the NaOH solution which is 30milliliters or 30mL for short.

The 0.15 M represents the concentration or strength of the NaOH solution and we can use this measurement to illustrate the rules for significant figures as well.

Rule #1 says that all non-zero digits are always significant, so any number 1 through 9 is significant like the 3 in the 1st measurement and the 1 and the 5 in the 2nd measurement.

Rule # 2 says that zeros to the left of a non-zero digit are never significant, like in the 0.15 measurement.

The zero is to the left of the 1 and therefore is not significant.

Since we covered all of the numbers in this measurement, it is safe to say that it has 2 significant figures.

Rule # 3 says that zeros in the middle of non zero digits are always significant. None of these measurements have zeros in the middle of non zero digits but let’s use the
number one thousand seven as an example.

Since the 1 and 7 are non-zero digits, they are significant.

And since the two zeros are in the middle of the 1 and 7, they too are significant, giving this measurement 4 significant figures.

Let’s make room for the fourth and final rule, which says, zeros to the right of non-zero digits are sometimes significant.

That sometimes holds true only if there is a decimal point and that decimal point can be anywhere in the number.

So in the 30.0 measurement, it’s important to point out that both zeros are to the right of the 3 and there is a decimal point so both zeros are significant, giving this measurement a total of 3 significant figures, which now completes the answer to this question.

01:47

Question # 77 from the January, 2012 Chemistry Regents

(See also Way # 64 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are percent composition.

You can find the formula for percent composition on Table T of the chemistry reference table.

The mass of oxygen represents the mass of part and ascorbic acid represents the whole, so we’ll need to know its mass.

Although the paragraph states that ascorbic acid has a molecular formula of C6H8O6 and a gram formula mass of 176 grams, it’s important to see how they came up with
that number.

So, first, we have to list all of the elements found in the formula.

Next, write down how many atoms there are for each element. There are 6 C’s, 8 H’s and 6 O’s.

Multiply the number of atoms by their respective atomic masses which can be found in the upper left hand corner for each element in the periodic table of elements.

Round the masses to the nearest whole number unless it tells you otherwise.

6 x 12 is 72, 8 x 1 is 8, 6 x 16 is 96.

Add up all of these numbers and you will get 176, the same formula mass mentioned in the paragraph.

This again represents the mass of whole.

The mass of oxygen represents the mass of part so we’ll use the 96 as our numerator.

Don’t forget to x by 100.

Since we only need a numerical setup, there is no need to solve the problem.

01:12

Question # 76 from the January, 2012 Chemistry Regents

(See also Way # 66 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are number of moles.

Table T of the chemistry reference table, has a formula to figure out the number of moles under the title mole calculations.

Since the question says that the orange contains 0.071 grams of vitamin C, that will represent the given mass, which we’ll write as our numerator.

The paragraph states that ascorbic acid has a gram formula mass of 176 grams per mole, which represents our denominator.

Divide 0.071 by 176 and you’ll get 4.034 x 10 to the negative 4 moles.

The 10 to the negative 4 simply means that the answer can also be written as the decimal 0.0004, which simply moved the decimal point 4 places to the left.

Section 11: Solutions
01:05

Question # 71 from the January, 2012 Chemistry Regents

(See also Way # 2 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are homogeneous mixture.

In a homogeneous mixture, the particles are evenly distributed, like in salt water.

The salt is dissolved throughout the water so while you can’t see, it’s in there.

To show that the particles in a homogeneous mixture are evenly distributed, we can take a sample from the top, middle, and bottom and see that they are all the same.

As opposed to a heterogeneous mixture, where the particles are not evenly distributed, for example, oil and water.

If samples from here are also taken from the top, middle and bottom, they will not be same.

So, you should know that all solutions are homogeneous mixtures and that the particles are evenly distributed.

01:50

Question # 70 from the January, 2012 Chemistry Regents

(See also Way # 69 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are Reference Table G.

Table G is quite large so we need to make some room for it.

Let’s see how to use Table G, beginning with the 20 degrees Celsius which refers to the temperature on the x axis.

Next, out of all of those lines, we want to focus our attention on hydrogen chloride gas or HCl, which is this line.

The solution contains 44 grams of HCl, which is around here on the Y axis.

However, we need to be careful here, because the 44 grams are dissolved in 200 grams of water meanwhile Table G measures solubility in 100 grams of water.

So, if 44 grams are dissolved in 200 grams of water, then half that amount, or 22 grams will dissolve in 100 grams of water, moving the green box down to about here.

The intersection of 22 g of HCl at 20 degrees Celsius in 100 grams of water puts us here, which is way below the line for HCl.

In terms of saturation, if the intersection point falls anywhere below the line, the type
of solution will be unsaturated.

If the intersection point falls anywhere on the line, the solution is considered to be saturated.

If the intersection point falls anywhere above the line, the solution is considered to
be supersaturated.

01:05

Question # 40 from the January, 2012 Chemistry Regents

(See also Way # 71 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are parts per million.

The formula for parts per million can be found on Table T of the chemistry reference table. Parts per
million is equal to the mass of the solute divided by the mass of the solution multiplied by 1 million.

A 2400 gram sample of an aqueous solution represents the mass of the solution, so we’ll make that our
denominator.

The 0.012 gram of NH3 represents the mass of the solute, so we’ll make that our numerator.

Divide 0.012 gram by 2400 gram and you get 0.000,005.

Multiplying that number by 1 million gets you 5 parts per million, making the answer choice 1.

01:51

Question # 42 from the January, 2012 Chemistry Regents

(See also Way # 72 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are the boiling point and freezing point of 100 grams of H2O.

If we look at a thermometer, the freezing point of H2O is 0 degrees Celsius. Let’s say right about here.

The boiling point of H2O is 100 degrees Celsius, which we’ll say is here. Don’t worry about the scale being small; we’re simply marking 2 points on a thermometer.

When a substance, such as CaCl2 is dissolved in water, a solution is formed and 2 things change as a result: The boiling point goes up and the freezing point goes down, so that instead of 100 degrees Celsius, the
new boiling point will be higher, let’s say 103 degrees Celsius.

And instead of 0 degrees Celsius, the new freezing point will be lower, let’s say negative 3 degrees Celsius.

Therefore, the answer will be choice 3, a higher boiling point and a lower freezing point.

How high or low these points go depends on the type of substance and the number of particles being dissolved.

CaCl2 is ionic so it will produce 3 ions when dissolved in water.

NaCl is also ionic but it will only yield 2 ions when dissolved in water.

C6H12O6, or the sugar glucose, remains as 1 molecule because it is covalent and so does not form ions.

The more particles a substance has, the greater the effect.

Section 12: Kinetics / Equilibrium
02:17

Question # 44 from the January, 2012 Chemistry Regents

(See also Way # 78 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are heat of reaction.

First, we need to recognize that each interval represents 10kilojoules per mole so let’s put this scale on this side, beginning with zero.

A and B represent the reactants of this reaction, so we can label arrow number 1 the potential energy of the reactants.

Because the arrow starts at 0 and ends at 20, 20 kj/mol is the potential energy of the reactants.

C is the product of this reaction, so we can label arrow number 2 the potential energy of the products.

Since the arrow starts at 0 and ends at 50, 50 kj/mol is the potential energy of the products.

The third arrow is for the heat of reaction, which tells us how much heat is released or absorbed.

We can symbolize the heat of reaction with a triangle H called delta H.

Delta H is equal to the PE products, which are at 50kj/mol, minus the PE reactants, which are at 20kj/mol, for a difference of 30kj/mol, making choice 3 the answer.

Arrow 4, called the activation energy, is the energy needed to start the reaction.

Since the arrow starts at 20 and ends at 60, it has a value of 40 kj/mole and would have been choice 4.

Arrow 5, called the activation complex, represents the total energy of the reaction.

Since the arrow starts at 0 and ends at 60, it has a value of 60 kj/mole and would have been choice 1.

Finally, to show this reaction with the energy involved, the 30 kj/mol would go on the reactants side to show that the heat was absorbed.

Had the heat been released, the 30 kj/mol would be written on the products side.

01:00

Question # 37 from the January, 2012 Chemistry Regents

(See also Way # 77 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are exothermic reaction.

An exothermic reaction is a reaction in which heat energy is released.

Alternatively, an endothermic reaction is when heat energy is absorbed.

Table I of the chemistry reference table lists the heats of reaction for many different reactions

So, let’s list the reactions out for all 4 of our choices, keeping in mind that we are looking for compounds formed from their elements.

With the heats of reactions listed on the right, it might be pretty obvious as to which choice is the correct answer, but if not, there is a little hint written at the bottom of table I that says, “A minus sign indicates an
exothermic reaction, making the answer choice 3.

00:49

Question # 24 from the January, 2012 Chemistry Regents

The keywords in this question are systems in nature.

Nature favors doing what is easiest.

Which activity is easier, or requires less energy: going from low to high or high to low?

Going from high energy toward low energy is easier, eliminating choices 3 and 4.

When it comes to entropy, or disorder, which is easier: keeping things in order or making a mess?

It’s much easier to reach a state of disorder than it is to keep things orderly.

Therefore, systems in nature tend to undergo changes toward lower energy and higher entropy, which is choice 2.

00:47

Question # 80 from the January, 2012 Chemistry Regents

(See also Way # 77 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are heat released.

The way to read this reaction is as follows:

2 moles of SO2 react with 1 mole of O2 to produce 2 moles of SO3 and 392 kJ of heat.

So if the production of 2 moles of SO3 releases 392 kj of heat, then 1 mole of SO3, which you get by cutting 2 moles in half, will release half as much heat or 196 kJ.

00:52

Question # 45 from the January, 2012 Chemistry Regents

(See also Way # 81 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is equilibrium.

Equilibrium sounds like the word equal may a play a role in the answer.

Choices 1 and 3 have the word equal in them so let’s eliminate choices 2 and 4 because they both say greater than.

By definition, equilibrium means that the rate of the forward reaction is equal to the rate of the reverse reaction.

So when it comes to a solution, particularly a saturated one, the rate of dissolving is equal to the rate of crystallization, making the answer choice 1.

01:15

Question # 79 from the January, 2012 Chemistry Regents

The keywords in this question are increasing the pressure.

The way to read this reaction is as follows:

2 moles of SO2 react with 1 mole of O2 to produce 2 moles of SO3 and 392 kJ of heat.

Increasing the pressure shifts the reaction to the side with fewest moles of gas.

The reactant side or the left side of the reaction has a combined 3 moles.

Meanwhile, on the products side or the right side of the reaction there are only 2 moles.

Therefore, the reaction will shift to the right, increasing the rate of the forward reaction.

So, in terms of collision theory, when the pressure in the cylinder is increased, the SO2 molecules and O2 molecules collide more frequently, producing more SO3.

00:55

Question # 81 from the January, 2012 Chemistry Regents

The keywords in this question are more O2 is added.

The way to read this reaction is as follows:

2 moles of SO2 react with 1 mole of O2 to produce 2 moles of SO3 and 392 kJ of heat.

So, if more O2 is added to the reaction, these particles will react with any remaining particles of SO2, using them up, to produce more SO3 and more heat.

So, in terms of the concentration of SO3, the concentration of SO3 increases.

Section 13: Acid / Base
00:59

Question # 30 from the January, 2012 Chemistry Regents

(See also Way # 83 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is base.

Table L of the chemistry reference table shows some of the most commonly used bases.

Most of the formulas for these bases have something in common: they end with an OH.

OH stands for hydroxide as their name suggests, making the answer choice 3.

So when an Arrhenius base, such as sodium hydroxide, is dissolved in water, it will yield positive sodium ions and negative hydroxide ions.

Aqueous ammonia, although not as obvious, also produces hydroxide ions when dissolved in water.

This occurs by one of the H’s in a water molecule joining the NH3 molecule to become NH4+, leaving behind a negative hydroxide ion, or OH-.

01:44

Question # 50 from the January, 2012 Chemistry Regents

(See also Way # 84 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are reversible and the reactant that donates an H+ ion.

Reversible means that the reaction can be read from left to right, which we call the forward reaction.

Or, if read from right to left, we would call this the reverse reaction.

Since the question mentions the forward reaction, NH3 and H2O will be the reactants and NH4 positive and OH negative will be the products.

Therefore, we can eliminate choices 3 and 4 because we need a reactant in the forward reaction.

If NH3 donates an H+ ion to H2O, we would get NH2 negative and H3O positive as the products, which isn’t the case.

But if H2O donates an H+ ion to NH4, we would get NH4positive and OH negative, which is the case, making the answer choice 2.

If the question asked about the reverse reaction, then NH4 positive and OH- would become the reactants and NH4+ would be the one who donates an H+ ion to OH negative to make NH3 and H2O the products.

02:10

Question # 48 from the January, 2012 Chemistry Regents

(See also Way # 86 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are pH and hydronium ions.

pH stands for the potential for Hydrogen, which measures the concentration of H+ ions in a solution.

When H ions are added to water it can form an H3O positive ion, also known as hydronium.

So either H+ or H3O+ can be used to represent an acid.

The ion OH-, known as hydroxide, represents a base.

The concentration of an acid or a base can be measured on the pH scale, which ranges from 0 to 14.

A pH of 7 is when the H+ ions equal the OH- ions making a solution neutral.

When the H+ ions are greater than the OH- ions, that’s when we get into the acid territory with 6 being the pH of the weakest acid and the lower we go, the stronger the acid gets.

When the H+ ions are less than the OH- ions, that’s when we get into the base territory with 8 being the pH of the weakest base and the higher we go, the stronger the base gets.

So when the pH is changed from 2 to 1, the acid becomes stronger because the hydronium ion concentration increases, making choices 1 and 3 incorrect.

For every increase in 1 on the pH scale, there is a 10 fold change in ion concentration, making the answer choice 4.

If the pH changed from 3 to 1, that would make the acid 100 times as strong.

If the pH changed from 4 to 1, that would make the acid 1000 times as strong.

The same is true for a base except here, the hydrogen ion concentration will decrease accordingly.

01:31

Question # 75 from the January, 2012 Chemistry Regents

(See also Way # 87 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are the indicator thymol blue.

Since acid and base solutions are both colorless, indicators, such as thymol blue, can tell us which solution we are dealing with by changing colors.

The color changes are based on the strength of the acid or base solution which is measured on the pH scale.

The pH scale ranges from 0 to 14 with 7, the halfway mark being neutral, like water.

A solution with a pH value less than 7 is considered to be an acid.

A solution with a pH value higher than 7 is considered to be a base.

Table M of the chemistry reference tables lists some of the most common acid-base indicators such as thymol blue.

If the pH of a solution is 8.0 or less, thymol blue will turn the solution yellow.

If the pH of a solution is 9.6 or greater, thymol blue will turn the solution blue.

If the pH is somewhere in the middle of 8.0 and 9.6, it will turn the solution green.

Since Vitamin C is also known as ascorbic acid, the pH of the solution should be less than 7, so adding thymol blue would turn the solution yellow.

01:35

Question # 64 from the January, 2012 Chemistry Regents

(See also Way # 85 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is neutralization.

Neutralization is a double replacement reaction where an acid reacts with a base to make water and salt.

In general, we can illustrate this using letters so that when compound AB reacts with compound CD, they will switch partners, making sure that for all compounds, the first ion in the compound is positive and the second ion is negative.

Let’s say that AB is the acid, CD is the base, AD is water and CB is a salt.

If we use the equation from the answer booklet, HNO3 is the acid, which will usually be one of the acids listed in Table K of the chemistry reference table and NaOH is the base, which will usually be a base listed in Table L of the chemistry reference table.

The H from the acid and the OH from the base will come together to form water, H2O.

Meanwhile, the Na from the base and the NO3 from the acid will come together to form NaNO3, a salt, because it contains a metal and a non-metal.

This H20 and the NaNO3 are the formulas that complete the equation for this neutralization reaction.

01:58

Question # 65 from the January, 2012 Chemistry Regents

The keyword in this question is concentration.

But just as equally as important is the word titration mentioned in the passage.

Titration is the process of combining an acid and a base until neutralization occurs.

Table T of the chemistry reference tables has a formula for titrations.

This formula has 4 variables: Ma and Mb which represent the concentrations of the acid and the base and Va and Vb which represent the volumes of the acid and the base.

Typically, you will be given 3 out of the 4 variables and you would need to solve for the fourth.

In this simple example, x is equal to 2 but don’t expect the numbers to always work out so nice and evenly, however the math will be the same.

When we use the formula in this question, Ma is what we are solving for so we’ll make that the x.

The 35.0 milliliters of HNO3 represents the volume of the acid.

The 0.15 M of NaOH represents the molarity of the base.

And the 30.0 milliliters of the NaOH represents the volume of the base.

Since the question only wanted a numerical setup, then this is all you would need to write.

Alternatively, you could set it up as if you were going to solve for x.

Finally, if the question did ask you to calculate the molarity of the acid, then you would multiply the numerators,
divide by the denominator and you would get 0.13 M as your answer.

Section 14: Electrochemistry
01:22

Question # 43 from the January, 2012 Chemistry Regents

(See also Way # 90 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is reduction.

Reduction means the gaining of electrons.

When electrons are gained, they will be written before the arrow when writing a reaction.

Therefore, we can eliminate choices 1 and 3, since the electrons are written after the arrow, which represents oxidation, or the losing of electrons.

Now, in choice 2, if an aluminum plus 3 ion were to gain 3 negative electrons, it would produce a neutral aluminum atom.

But since aluminum started out as a neutral atom, and not as a plus 3 ion, this choice is also incorrect.

Choice 4 is correct because copper does start out as a plus 2 ion and ends up as a neutral copper atom
so we say it was reduced, or underwent reduction, by gaining 2 electrons.

The 3 in front simply means that if each copper ion gains 2 electrons then 3 copper ions will gain a total of 6 electrons.

02:05

Question # 29 from the January, 2012 Chemistry Regents

(See also Way # 92 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are voltaic cell.

A voltaic cell is like a homemade battery and may look something like this.

A battery produces electricity by having 2 metals of different reactivity levels, such as copper and silver, so that one metal will lose electrons more easily than the other.

We can refer to Table J of the chemistry reference table to see which element is more reactive.

Since copper is higher than silver on Table J, it is more reactive and will be the one to lose electrons meanwhile silver will be the one to gain electrons.

We can write the reaction for this as follows: Cu in the solid phase plus 2 Ag positive ions that are aqueous, or dissolved in water, will produce an aqueous Cu positive 2 ion plus 2 Ag silver in the solid phase.

The Cu solid refers to this electrode where electrons will be lost.

The Ag positive ions will fill this container.

The Cu positive ions will fill this container.

And the Ag solid refers to this electrode where electrons will be gained.

When this battery is in operation, 2 electrons will leave Cu solid, travel through the wire and be attracted to the Ag positive ions in solution.

As a result, the Ag positive ions will gain these electrons forming pure solid silver on the Ag electrode causing it to increase in mass.

Simultaneously, the Cu electrode decomposes, shedding Cu positive ions into the solution.

While the electrons traveled through the wire, positive and negative ions move through the salt bridge to keep the flow of electricity continuous between containers, making the answer choice 3.

01:30

Question # 61 from the January, 2012 Chemistry Regents

(See also Way # 93 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are power source.

According to the passage, an operating electrolytic cell is used to plate silver onto a nickel key.

In order for this to happen, the silver ions from the silver nitrate solution will undergo reduction, which is the gaining of electrons, according to the following reaction.

The Ag positive ions will be attracted to the key so that it can gain negatively charged electrons being supplied by the power source. As a result, the silver ions will neutralize, coating the key with pure silver.

At the same time, oxidation, which is the loss of electrons, occurs at the silver electrode, according to the following reaction.

In this reaction, the mass of the silver electrode decreases as the Ag atom turns into an Ag positive ion by losing an electron.

The newly formed Ag positive ions will enter the solution and the electrons will move up the electrode to head back to the power source to complete the circuit.

Therefore, the power source provides electrical energy for both of these reactions to occur.

01:32

Question # 60 from the January, 2012 Chemistry Regents

(See also Way # 94 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is cathode.

Cathode is defined as the site where reduction occurs.

Reduction is the gaining of electrons.

Since electrons are negatively charged, they flow out of a power source, such as a battery, from the negative pole and wind up at the key, which is made of solid nickel.

The key is immersed in a solution of silver nitrate, or AgNO3, which is really made up of Ag positive ions and NO3 negative ions dissolved in water.

The Ag positive ions will be attracted to the negative electrons at the key, gaining them to form pure silver on the key in a process called electroplating.

Therefore, the key, or solid nickel will be the answer.

Meanwhile, oxidation, or the loss of electrons, will occur at the silver electrode where the Ag solid will turn into an Ag positive ion by losing an electron.

As this happens, the mass of the silver electrode decreases, with the Ag positive ions moving to join with the negative nitrate ions and the electrons moving up the electrode to head back to the battery to complete the circuit.

01:44

Question # 62 from the January, 2012 Chemistry Regents

The keywords in this question are silver electrode.

The silver electrode is attached to the positive end of the power source.

The power source supplies the reaction with electrons, which are negatively charged, and therefore, flow out of the power source from the negative pole and wind up at the key.

The key is immersed in a solution of silver nitrate, or AgNO3, which is really made up of Ag positive ions and NO3 negative ions dissolved in water.

The Ag positive ions will be attracted to the negative electrons at the key, undergoing a reduction reaction, which is the gaining of electrons.

Here is the reaction for the reduction that occurs, which uses up Ag positive ions from the solution to coat the key with pure silver.

As the cell operates, oxidation, or the loss of electrons, occurs at the silver electrode.

In the oxidation reaction, the Ag atoms will turn into Ag positive ions by losing an electron, causing the mass of the silver electrode to decrease.

The newly formed Ag positive ions will move to join forces with the negative nitrate ions and the electrons will move up the electrode to head back to the battery to complete the circuit.

Section 15: Organic Chemistry
01:21

Question # 58 from the January, 2012 Chemistry Regents

(See also Way # 97 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is unsaturated.

Unsaturated is when a hydrocarbon has at least one double or triple bond.

As opposed to saturated, when a hydrocarbon has single bonds only.

Considering that every carbon atom can form up to four bonds, a hydrocarbon that has single bonds only has the ability to hold more hydrogen atoms, making it saturated.

Every time a bond is added between carbon atoms, the hydrocarbon loses 2 hydrogen atoms, making it unsaturated.

Adding another bond between different carbon atoms would have the same effect, causing the hydrocarbon to lose 2 more hydrogen atoms, making it even more unsaturated.

Magically, we’ve made this hydrocarbon resemble hydrocarbon 1, reinforcing the fact that it is unsaturated.

Having a triple bond between carbon atoms has the same effect as having two separate double bonds.

So, in terms of bonds, both hydrocarbons have at least one multiple covalent bond between 2 carbon atoms.

00:50

Question # 59 from the January, 2012 Chemistry Regents

(See also Way # 99 on "100 Ways to Pass the Chemistry Regents!")

The keyword in this question is isomers.

Isomers are compounds that have the same molecular formulas, like in this case, these compounds both have the molecular formula of C5H8.

But different structural formulas.

Note the differences in bond number and location between carbon atoms as well as the placement of all of the hydrogen atoms.

So in terms of structural formulas and molecular formulas, this answer should be sufficient.

00:24

Question # 26 from the January, 2012 Chemistry Regents

(See also Way # 98 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are functional groups.

If we take a look at Table R of the chemistry reference table, we see that organic compounds contain functional groups, making the answer choice 1.

Functional groups can be an element or a group of elements that change the properties of an organic compound.

01:13

Question # 27 from the January, 2012 Chemistry Regents

(See also Way # 98 on "100 Ways to Pass the Chemistry Regents!")

The keywords in this question are group 17 of the periodic table.

Let’s take a look to see which elements are found in Group 17. We need to be on the lookout for fluorine, chlorine, bromine or iodine.

In order to identify which class of compounds contains a group 17 element, we need to refer to Table R of the chemistry reference table.

The first choice, aldehyde, contains a C, an H and an O, but nothing from Group 17, so this is incorrect.

The 2nd choice, amine, only contains an N, which is not in Group 17, making this choice incorrect.

Choice 3, an ester, contains only C and O, making this choice incorrect.

Choice 4 is correct because a halide can contain any of the Group 17 elements.

Halide gets its name from the word halogen, which is the name of the Group 17 elements.

01:34

Question # 46 from the January, 2012 Chemistry Regents

The keywords in this question are addition reaction.

An addition reaction is an organic reaction involving alkenes or alkynes and the formation of one product.

Table Q of the chemistry reference table has information regarding alkenes and alkynes.

An alkene is a hydrocarbon that contains a double bond between carbon atoms, whereas an alkyne is a hydrocarbon that contains a triple bond between carbon atoms.

Ethene is the alkene used in this question, which has this structural formula.

Since ethene is reacting with chlorine, which is Cl2, we can automatically get rid of choices 1 and 4.

The reason for this is due to the Law of conservation of matter which states that matter cannot be created or destroyed.

So if we only began with 2 chlorines, then we can’t gain or lose anymore than we started with.

The Cl2 can also be written like this with a single bond between the 2 chlorines.

During an addition reaction, one of the bonds in the double bond between the carbon atoms in ethene will break, allowing the 2 chlorines to be added to the molecule, making the correct answer, choice 2.

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