Practice tests with solutions

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Index1 Kinetic Theory and Diffusion …………………………………………………………………………………… 3234567891011121314151617181920212223242526

ACTIVITIES

1.1. Benzene melts at 5.5°C and boils at 80.1°C. Which one of the following statements is true about benzene?

A The only movement that the particles in benzene have at a temperature of 20°C is vibration about a fixed point.

B At 100°C, the particles in benzene are well scattered and moving at random.

C At 0°C, benzene is a liquid.

D If you cooled benzene from 100°C to 50°C, the change of state that happens at 80.1°C is called sublimation.

1.2. Choose the word from the list below that best describes the change of state which happens when a purple vapour turns into a purple solid on cooling.

A freezing

B sublimation

C condensation

D evaporation

1.3. Choose the word from the list below that best describes the change of state which happens when a few drops of water on a bench gradually disappear.

A freezing

B sublimation

C condensation

D evaporation

1.4. Choose the word from the list below that best describes the change of state which happens when colourless liquid naphthalene turns into white crystals.

A freezing

B sublimation

C condensation

D evaporation

1.5. Which one of the following statements about particles in solids, and liquids is not true?

A When a solid is heated, the particles vibrate faster and faster until the forces holding them together are broken, and they become free to move around.

B Particles in a liquid are quite closely packed, but have some freedom to move around.

C When a liquid is heated, the heat energy makes the particles lighter, which is why they escape more easily from the surface of a hot liquid than a cold one.

D For most substances, the particles in the liquid are slightly further apart than they are in the solid, and so the liquid is less dense than the solid.

1.6. The relative masses of the particles of four gases are:

helium 4 methane 16 oxygen 32 sulfur dioxide 64

The gas which diffuses most quickly is

A helium

B methane

C oxygen

D sulfur dioxide

1.7. Experiments show that if some brown bromine vapour is released into a large flask which is full of air, the colour spreads evenly through the flask over a minute or so. However, if the bromine is released into the same flask which contains a vacuum, the colour fills the whole flask in a fraction of a second. The reason for this is

A Bromine particles travel at about 200 metres per second in a vacuum, but only 100 metres per second through the air.

B Bromine particles are heavier than air particles, and heavy particles move more slowly than lighter ones.

C The vacuum sucks the bromine into it.

D In air, bromine particles keep bumping into air particles which slows the process down. In a vacuum, nothing gets in their way.

1.8. This question is about an experiment to find out the relative speeds at which the gases ammonia and hydrogen chloride diffuse.

Which one of the following statements is not true?

A Hydrogen chloride particles travel faster than ammonia particles.

B The white ring is solid ammonium chloride produced where the ammonia and hydrogen chloride meet.

C Ammonia particles are lighter than hydrogen chloride particles.

D The time taken for the white ring to form will depend on the length of the tube.

1.9. Crystals of potassium manganate(VII) are deep purple, and produce a rich purple solution in water. If you drop some crystals into a beaker of water, eventually the whole solution becomes evenly purple. Which one of the following processes is not happening in the beaker?

A Particles of potassium manganate(VII) are breaking away from the crystal and moving between the water particles, eventually reaching all parts of the liquid.

B The water particles are close together, but moving around.

C The potassium manganate(VII) melts to give liquid potassium manganate(VII).

D Some water particles are breaking away from the surface of the solution to form water vapour.

1.10. Sometimes, before an injection, for example, a doctor or nurse might clean your skin by rubbing it with some alcohol. This often feels very cold, even though it is at room temperature. The reason for this is

A Alcohol has slow moving particles, and slow moving particles are colder than fast moving ones.

B As the alcohol evaporates, heat is needed to break the attractions between the particles. This heat is taken from your skin.

C This has nothing to do with particles. It is a reaction caused by fear of injections.

D The alcohol freezes in contact with your skin.

ACTIVITIES

2.1. Which one of the following statements is true for all elements?

Neutral atoms of the same element contain

A equal numbers of protons and neutrons.

B equal numbers of protons and electrons.

C equal numbers of neutrons and electrons.

D equal numbers of protons, neutrons and electrons.

2.2. Which one of the following statements about the isotopes of a particular element is wrong?

All the isotopes of a particular element have neutral atoms having

A the same atomic number.

B the same number of protons.

C the same number of neutrons.

D the same number of electrons.

2.3. You will need to refer to a copy of the Periodic Table to answer this question.

Which one of the following elements has the electronic structure in this diagram?

A beryllium

B fluorine

C neon

D chlorine

2.4. You will need to refer to a copy of the Periodic Table to answer this question.

Which one of the following electronic structures represents sulfur?

A 2,8,6

B 2,8,8,8,6

C 2,8,18,4

D 2,6,8

2.5. You may need to refer to a copy of the Periodic Table to answer this question.

Which one of the following electronic structures does not represent a noble gas?

A 2,8

B 2

C 2,8,18,8

D 2,8,8,2

2.6. You will need to refer to a copy of the Periodic Table to answer this question.

Which one of the statements about an atom with an atomic number of 17, and a mass number of 35 is wrong?

A The atom is an isotope of chlorine.

B The electronic structure is 2,8,7.

C The atom contains 17 neutrons.

D It is an isotope of the same element as one with an atomic number of 17 and a mass number of 37.

2.7. You will need to refer to a copy of the Periodic Table to answer this question.

Which one of the following lists of electronic structures consists only of atoms of elements in the same Group of the Periodic Table?

A 2,8,1 2,8,2 2,8,3

B 1 2,1 2,8,1

C 2,7 2,8,1 2,8,5

D 2,2 2,8,2 2,8,8,2

2.8. You will need to refer to a copy of the Periodic Table to answer this question.

How many electrons are there in the outer level of a strontium atom? The atomic number of strontium is 38.

A 2

B 4

C 6

D 8

2.9. A particle consisted of a nucleus with 11 protons and 12 neutrons. Around the outside of it were 10 electrons arranged in two levels: 2,8. Which one of the following statements is not true?

A The mass number of the particle is 23.

B The particle isn’t a neutral atom. It has a charge of +1.

C The particle has a noble gas structure of its electrons.

D The particle is a neon atom.

2.10. This question contains information which is new to you.

Uranium-235, an isotope of uranium with a mass number of 235 and an atomic number of 92, is radioactive. It has an unstable nucleus which loses an alpha-particle. Alpha-particles consist of 2 protons and 2 neutrons. Which one of the following isotopes is produced during this process in addition to the alpha-particle?

A uranium-231

B radium-231 (the atomic number of radium is 88)

C thorium-231 (the atomic number of thorium is 90)

D plutonium-231 (the atomic number of plutonium is 94)

Chapter 1 Kinetic Theory and Diffusion1.1. Answer: B

Comment

If you look at the melting and boiling temperatures, benzene is a solid up to 5.5°C. It is a liquid from 5.5°C to 80.1°C, and then a gas above that.

A is wrong because the description of the movement of the particles is for a solid, and at 20°C, benzene would be a liquid.

B describes a gas, and benzene would be a gas at 100°C – that’s the right answer.

C is wrong because it would be a solid at this temperature.

Sublimation is a change from solid to gas and vice versa. In D, we are going from gas to liquid, and so that’s wrong.

1.2. Answer: B

Comment

The change from a vapour straight to a solid is sublimation. You just have to know that.

1.3. Answer: D

Comment

This is a simple question, and normal everyday use of words tells you that it is evaporation.

1.4. Answer: A

Comment

A change of state from liquid to solid is freezing. It doesn’t matter how complicated the solid is – the word applies to naphthalene just as much as to water.

1.5. Answer: C

Comment

Be very careful when you are asked to choose an answer which is not true, especially if you are used to questions asking you for a true answer. It is very easy to fall into the trap of choosing the first answer you come to which sounds correct. But you don’t want a correct answer – you want the untrue one.

In this case, A, B and D are all correct statements, but C isn’t. Heating a particle up gives it energy and makes it move faster (which is why the particles escape more easily from the surface of a hot liquid), but it has no effect whatsoever on the mass of the particles. It doesn’t make them ‘lighter’, and that’s why C is the incorrect statement.

1.6. Answer: A

Comment

You have to know that light particles diffuse faster than heavier ones. The lightest particle you are given is helium,

Incidentally, if you had to guess this, it doesn’t make sense to guess either methane or oxygen. The question implies that speed of diffusion has something to do with the mass of the particles, in which case the correct answer is going to be either the lightest one or the heaviest one. To choose an ‘in between’ answer is just silly.

1.7. Answer: D

Comment

A is wrong on two counts. If the figures you were given were true, then the bromine would diffuse twice as fast in a vacuum as in air. If you look at the question, the difference is much, much greater than that. Secondly, the speed of a particle depends on its temperature, not what is around it. There has to be a better explanation than this.

B is tricky! The statement is entirely true, but it isn’t a reason for the descriptions given in the question. Don’t fall into this sort of trap.

C is the sort of answer which would be given by someone who knows no science! Particles in gases are moving around at random. What can possibly ‘suck’ them into a space? Sucking implies a pulling movement, and there is nothing to do the pulling.

D is the correct answer.

1.8. Answer: A

Comment

Start with B. This is true – the white ring is ammonium chloride formed from the reaction between ammonia and hydrogen chloride gases. You have just got to know that. Why is it closer to the hydrochloric acid end of the tube? Because the ammonia has travelled further in the time. That implies that the ammonia particles travel faster than the hydrogen chloride ones. That means that A looks like the wrong statement you need.

But you need to check the other two statements as well. Ammonia particles travel faster because they are lighter, and so C is a true statement – and you are looking for a false one. D is obviously also true. If you had

a tube a kilometre long it is going to take a very much longer time for the ring to form than if it was 10 cm long.

So A is the only untrue statement.

1.9. Answer: C

Comment

A, B and D are all true statements. If A wasn’t true, you wouldn’t get colour evenly spread through the solution. B is a simple statement of the arrangement of particles in a liquid, and D describes the fact that water will tend to evaporate.

That leaves C. This is false because of the use of the words ‘melts’ and ‘liquid’. A solid melts if you heat it and a liquid is formed. In this case, you aren’t heating it. The solid is dissolving to form a solution, and that’s not the same thing as melting to form a liquid. You have to be careful to use your words in the proper scientific sense.

1.10. Answer: B

Comment

The correct answer is B. Evaporation needs energy to overcome the attractions between the molecules, and this energy has to come from somewhere. In this case, your warm skin is a good source of energy. If your skin loses energy in this way, then it cools.The other answers are mainly silly! Any answer like C is almost certainly bound to be wrong – it is just there because the person setting the question couldn’t think of anything more sensible. A is wrong because you are told that everything is at room temperature. The alcohol is at room temperature to start with, and so can’t be ‘colder’. And D is wrong because it requires the alcohol to freeze in contact with your warm skin. Things don’t freeze if you warm them up.

Chapter 2 Atomic Structure

2.1. Answer: B

CommentA neutral atom has to have the same number of positively charged protons as negatively charged electrons, otherwise it wouldn’t be neutral. The number of neutrons can vary because they aren’t charged.

2.2. Answer: C

CommentIsotopes are atoms of the same element (the same atomic number, and so the same number of protons), but with a different mass number. The mass number is the sum of the number of protons and neutrons. That means that isotopes of an element must have different numbers of neutrons. So statement C is the wrong one. Don’t forget that you are looking for a wrong statement.

2.3. Answer: B

CommentThe atom has 9 outer electrons, and so must have 9 protons. That means that its atomic number is 9. The atom with an atomic number of 9 is fluorine.

2.4. Answer: A

CommentSulfur has an atomic number of 16, and its electrons will be arranged 2,8,6. The most likely mistake is to take the wrong figure of 32 (the relative atomic mass) from the Periodic Table. If you made that mistake, make sure that you don’t do it again.

2.5. Answer: D

CommentApart from helium with just 2 electrons, all the other noble gases have 8 electrons in their outer level. So D can’t be a noble gas. You could easily check this by adding up the total number of electrons in each atom – which will be the same as its atomic number. Check the Periodic Table to see where each of the atoms is. Because you can quickly check it in this way, this should be a question which is practically impossible to get wrong!

2.6. Answer: C

Comment

The atomic number means that the atom has 17 protons and 17 electrons. The mass number of 35 is the sum of the number of protons and neutrons, and so there must be 18 neutrons. You can see immediately that C is wrong.

2.7. Answer: D

CommentAtoms in the same Group of the Periodic Table have the same number of electrons in their outer level. That means that A and C must be wrong. That leaves two possibilities.

The answer is D – not B. In B, the atom with just 1 electron is hydrogen, and hydrogen isn’t in Group 1 of the Periodic Table – it is out on its own at the top of the table. You might argue that this is a bit sneaky, but given that there are two possibilities, you have to look at them carefully.

You could be sure of getting this question right, without any thinking at all, if you just added up all the electrons in each atom, and found out where each element is in the Periodic Table. That would take longer to do, of course.

2.8. Answer: A

CommentIf you look up strontium in the Periodic Table, you will find that it is in Group 2. All elements in Group 2 have 2 electrons in their outer level. Whatever you do, don’t try to work out the structure as 2,8, (etc). Once you get beyond calcium (atomic number 20) this is too difficult to do at this level. The simple initial pattern breaks down after this.

2.9. Answer: D

CommentIf the atom contains 11 protons, it is sodium – not neon. That means that the untrue statement is D. The only unfamiliar answer is possibly B. Since the particle contains 11 protons, but only 10 electrons, it isn’t a neutral atom. Because it has 1 more proton than electron, it must have a charge of +1. This is known as an ion, and is how sodium exists in all of its compounds. You may not have come across this yet, but that doesn’t matter.

2.10. Answer: C

CommentThe original uranium-235 contained 92 protons. It loses 2 of these, and so the new atom has an atomic number of 90. It loses a total of 2 protons and 2 neutrons, and so the mass number falls by 4. So the new atom has a mass number of 231. The right answer is therefore C. This is an easy question – don’t be put off by a question just because it looks unfamiliar.