Chemistry Paper 2

Question 1

The amount of water vapour in today’s atmosphere is much less than the amount
in the Earth’s early atmosphere.
Explain why the amount of water vapour in the atmosphere has decreased.

Answer 1

• Earth temperatures cooled
• water vapour condensed forming oceans

Question 2

At the end of the experiment, the apparatus and its contents are allowed to
cool before the final volume of gas is measured.

The apparatus and its contents must be allowed to cool because

Answer 2

• The gas has expanded when it is hot

Question 3

The Earth’s earliest rocks contained iron sulfide and no iron oxide.
Later the rocks contained iron oxide as well as iron sulfide.
Explain what happened to allow this change to occur.

Answer 3

• oxygen increased in atmosphere
• iron is oxidised

Question 4

Describe what you would see if damp, blue litmus paper is placed into chlorine gas.

Answer 4

• blue litmus first turns red
• then it bleaches

Question 5

Describe what is meant by a covalent bond.

Answer 5

• shaired pair of electrons

Question 6

Explain why chlorine is a gas, rather than a liquid, at room temperature.

Answer 6

• has a low boiling point
• intermolecular forces are weak and take little energy to break

Question 7

When the gas hydrogen chloride, HCl, is dissolved in water, a solution forms.
Blue litmus paper dipped in this solution turns red.
State why the litmus paper turns red.

Answer 7

• solution is acidic (Has H+ ions)

Question 8

Explain, in terms of electronic configurations, the increase in reactivity from lithium to sodium to potassium.

Answer 8

• outer electron becomes
  further from the nucleus
• so outer electron more easily lost

Question 9

Which of the following is a trend in a property of the fractions obtained from the top of the column to those obtained from the bottom?

Answer 9

• the viscosities increase

Question 10

Explain why alkanes are described as hydrocarbons.

Answer 10

• compounds containing only carbon and hydrogen atoms

Question 11

Describe what is seen when chlorine water is added to potassium bromide
solution and the mixture shaken.

Answer 11

• potassium bromide solution colourless
• mixture turns yellow

Question 12

A solid ionic compound is dissolved in water to form a solution.
Describe a simple experiment to show that charged particles are present in this solution.

Answer 12

• carry out electrolysis experiment
• need a cathode and anode and power supply connected to it
• need ammeter to show the current

Question 13

State a change that can be made to the apparatus in Figure 6 to measure the
volumes of gas more accurately.

Answer 13

• gas syringe

Question 14

Calcium reacts with water to form calcium hydroxide,
Describe what would be seen when a piece of calcium is dropped into a
container of water.

Answer 14

• hydrogen produced as a gas so there
  would be bubbles
• calcium hydroxide produced as a
  solid so the water would go cloudy

Question 14

Calcium reacts with water to form calcium hydroxide,
Describe what would be seen when a piece of calcium is dropped into a
container of water.

Answer 14

• hydrogen produced as a gas so there
  would be bubbles
• calcium hydroxide produced as a
  solid so the water would go cloudy

Question 15

Fractions of crude oil contain alkanes.
A sample of decane, C10H22, was cracked using the apparatus in Figure 4.
This produced a mixture of products, including ethene.
Explain how ethene is produced using the apparatus in Figure 4.

Answer 15

• when the decane is heated, turns to a gas
• gas breaks down as it comes in contact with hot porous pot
• large molecules of decane produce
  smaller molecules, including ethene

Question 16

A student investigated the rate of reaction between dilute hydrochloric acid and marble chips (calcium carbonate).
Calcium chloride, carbon dioxide and water are formed.
Complete and balance the equation for the reaction.

Answer 16

• CaCO3 + 2HCl → CaCl2 + CO2 + H2O

Question 17

The order of reactivity of chlorine, bromine and iodine can be determined by
carrying out displacement reactions.
Explain how displacement reactions can be used to show the reactivity of these
three elements.

Answer 17

• order of reactivity: chlorine > bromine > iodine
• add (aqueous) chlorine to a solution of potassium bromide, the solution turns orange/yellow
• bromine is produced, Cl2 + 2KBr → Br2 + 2KCl
• chlorine is more reactive, displaces bromine
• add (aqueous) bromine to a solution of potassium iodide, the solution turns brown
• iodine is produced, Br2 + 2KI → I2 + 2KBr
• bromine is more reactive displaces iodine
• add (aqueous) chlorine to a solution of potassium iodide, the solution turns brown
• iodine is produced, Cl2 + 2KI → I2 + 2KCl
• chlorine is more reactive, displaces iodine