O LevelChemistryCambridgeExam Questions1. States of Matter1.2 Diffusion

Diffusion (Cambridge O Level Chemistry)

Exam Questions

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1.2 Diffusion

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1.2 Diffusion

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1a8 marks

Concentrated ammonia solution gives off ammonia gas. Concentrated hydrochloric acid gives off hydrogen chloride gas. Ammonia, NH3, and hydrogen chloride, HCl, are both colourless gases. Ammonia reacts with hydrogen chloride to make the white solid ammonium chloride.

Apparatus is set up as shown.

cie-igcse-sq-1-1-q2

After ten minutes a white solid forms in the tube where the gases meet.

i)
Write the chemical equation for the reaction of ammonia with hydrogen chloride.
[1]
ii)
Name the process by which the ammonia and hydrogen chloride gases move in the tube.
[1]
iii)
At which point, A, B, C or D, does the white solid form? Explain why the white solid forms at that point.
[3]
iv)
The experiment was repeated at a higher temperature.
Predict how the results of the experiment would be different. Explain your answer.
[3]

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1b6 marks

Some of the white solid is removed from the tube and dissolved in water.

Describe how the white solid could be tested to show it contains:

i)
Ammonium ions.
Test ...........................
Result .......................
[3]
ii)
Chloride ions.
Test .........................
Result .....................

[3]

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1c4 marks

The diagram shows the electron arrangement in a molecule of ammonia, showing only outer shell electrons.

cie-igcse-sq-1-1-q2b
i)
State the type of bonding in ammonia.
[1]
ii)
Hydrazine, N2H4, is another compound of nitrogen and hydrogen.
Complete the diagram to show the electron arrangement in a molecule of hydrazine,
showing only outer shell electrons.
cie-igcse-sq-1-1-q2bii
[3]

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1d3 marks

Nylon and proteins are both polymers containing nitrogen.

i)
Name the linkages found in the polymers of nylon and protein.

[1]

ii)
Describe one difference in the structures of nylon and protein.
[1]
iii)
What is the general name given to the products of hydrolysis of proteins?
[1]

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1e1 mark

Suggest the structure of the monomer used to make the polymer shown.

cie-igcse-sq-1-1-q2e

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1a3 marks

A small amount of liquid bromine is added to a container which is then sealed.

Br2(l) → Br2(g)

Use the ideas of the Kinetic Theory to explain why, after about an hour, the bromine molecules have spread uniformly to occupy the whole container.

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1b6 marks

The diagrams below show simple experiments on the speed of diffusion of gases.

1-2-q-2b-i
1-2-q-2b-ii

Complete the following explanations. Diagram 1 has been done for you.

Diagram 1
There is air inside and outside the porous pot so the rate of diffusion of air into the pot is the same as the rate of diffusion of air out of the pot. The pressure inside and outside the pot is the same so the coloured liquid is at the same level on each side of the tube.

Diagram 2.

................................

Diagram 3

................................

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2a5 marks

Acid-base reactions are examples of proton transfer.

Ethylamine is a weak base and sodium hydroxide is a strong base.

i)
In terms of proton transfer, explain what is meant by the term weak base.
[2]
ii)
Given aqueous solutions of both bases, describe how you could show that sodium hydroxide is the stronger base. How could you ensure a ‘fair’ comparison between the two solutions?
[3]

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2b4 marks

Ethylamine reacts with acids to form salts.

CH3CH2NH2      +     HCl    →   CH3CH2NH3Cl

                                                                ethylammonium chloride

i)
Complete the equation for the reaction between sulfuric acid and ethylamine. Name the salt formed.

......  CH3CH2NH2       +       ............     →     .........................

Name of salt ........................................................................
[3]
ii)
Amines and their salts have similar chemical properties to ammonia and ammonium salts.
Suggest a reagent that could be used to displace the weak base, ethylamine, from its salt ethylammonium chloride.
[1]

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2c5 marks

Gases diffuse, which means that they move to occupy the total available volume.

i)
Explain, using kinetic particle theory, why gases diffuse.
[2]
ii)
When the colourless gases hydrogen bromide and ethylamine come into contact, a white solid is formed.

CH3CH2NH2 (g) + HBr (g)     →     CH3CH2NH3Br (s)
     white solid

The following apparatus can be used to compare the rates of diffusion of the two gases ethylamine and hydrogen bromide.

1-3-q1


Predict at which position, A, B or C, the white solid will form. Explain your choice.

[3]

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3a2 marks

Different gases diffuse at different speeds.

i)
What is meant by the term diffusion?
[1]
ii)
What property of a gas molecule affects the speed at which it diffuses?

[1]

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3b2 marks

Helium is a gas used to fill balloons. It is present in the air in very small quantities. Diffusion can be used to separate it from the air.
Air at 1000°C is on one side of a porous barrier. The air which passes through the barrier has a larger amount of helium in it.

i)
Why does the air on the other side of the barrier contain more helium?
[1]
ii)
Why is it an advantage to have the air at a high temperature?
[1]

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3c3 marks

Most helium is obtained from natural gas found in the USA. Natural gas contains methane and 7% helium. One possible way to obtain the helium would be to burn the methane.

i)
Write an equation for the complete combustion of methane.
[1]
ii)
Suggest why this would not be a suitable method to obtain the helium.
[1]
iii)
Suggest another method, other than diffusion, by which helium could be separated from the mixture of gases in natural gas.
[1]

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4a5 marks

Kinetic theory explains the properties of matter in terms of the arrangement and movement of particles.

Nitrogen is a gas at room temperature. Nitrogen molecules, N2, are spread far apart and move in a random manner at high speed.

i)
Draw the electronic structure of a nitrogen molecule.
Show only the outer electron shells.

[2]

ii)
Compare the movement and arrangement of the molecules in solid nitrogen to those in nitrogen gas.

[3]

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4b2 marks

A sealed container contains nitrogen gas. The pressure of the gas is due to the molecules of the gas hitting the walls of the container.

Use the kinetic theory to explain why the pressure inside the container increases when the temperature is increased.

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4c3 marks

The following apparatus can be used to measure the rate of diffusion of a gas.

cie-igcse-sq-1-1-qac

The following results were obtained.

gas temperature/ oC rate of diffusion in cm3 / min
nitrogen 25 1.00
chlorine 25 0.63
nitrogen 50 1.05

i)
Explain why nitrogen gas diffuses faster than chlorine gas.

[2]

ii)
Explain why the nitrogen gas diffuses faster at the higher temperature.
[1]

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