Paper 1 Questions

Question 1

Ammonium nitrate is produced from ammonia and nitric acid on a large scale in industry. Ammonium nitrate can also be made in the laboratory by titrating ammonia solution with dilute nitric acid.
Ammonium nitrate crystals can then be obtained by evaporating off some of the water from the solution.
Give two reasons why this laboratory method is not suitable for use on a large scale in industry. [2]

Answer 1

• volumes of solution too large for titration method (1)
• large volumes of liquid need to be heated and then allowed
  to crystallise (1)

Question 2

When there are alternative methods of producing a product, the final pathway is
chosen by considering atom economy, cost of energy, yield of product and rates
of reactions.
State another factor that should also be considered. [1]

Answer 2

equilibrium position/usefulness of by-products [1]

Question 3

Give a reason why adding hydroxide ions to an acid solution leads to an increase in pH. [1]

Answer 3

hydroxide ions react with hydrogen ions and reduce the hydrogen ion concentration therefore increase pH (1)

Question 4

Describe one similarity and one difference between the industrial production of ammonium sulfate and the laboratory preparation of ammonium sulfate. [2]

Answer 4

a similarity from :
- both use sulfuric acid (1)
- both (are examples of) neutralisation (1)
and a difference from :
- the industrial process is on a much
- larger scale than the laboratory process / ORA (1)
- the industrial process involves more stages than the laboratory process / ORA (1)
- ammonia is a gas in the industrial process but a solution in the laboratory process (1)
- laboratory preparation uses titration and crystallisation (1)

Question 5

Explain why dilute hydrochloric acid is described as a strong acid [2]

Answer 5

an explanation linking
* fully dissociates (1)
* to form {H+/hydrogen} ions (1)

Question 6

Calcium and potassium react with water in similar ways.
One similarity in the reactions is that hydrogen gas is produced.
State one other similarity in the products of the reactions of calcium and potassium with water. [1]

Answer 6

both form a hydroxide

Question 7

After evaporation, the mass of the potassium chloride was determined.
The theoretical yield of the experiment was 0.70g.
The actual yield was 0.84g.
This gave a percentage yield greater than 100%.
State why the actual yield is greater than the theoretical yield [2]

Answer 7

{the salt/solid/potassium chloride} was still wet/ not all of the water had been evaporated off

Question 8

Copper carbonate is added to the acid in the flask.
The copper carbonate is added one spatula measure at a time until the reaction has finished.
State two observations that would show the reaction has finished. [2]

Answer 8

Any TWO from
* no more bubbles / fizzing (1)
* no further change in colour (1)
* {solid / copper carbonate} remains at bottom of flask / no more {solid /copper carbonate} dissolves (1)

Question 9

Calcium nitrate and calcium carbonate are both ionic compounds.
Calcium nitrate mixed with water behaves as an electrolyte.
Calcium carbonate mixed with water does not behave as an electrolyte.
Explain, in terms of solubility and movement of ions, this difference in behaviour (2)

Answer 9

• nitrate is soluble (1)
• carbon is insoluble (1)
• so ions free to move in solution (1)

Question 10

When a solution of sodium sulfate is electrolysed, the products formed at the electrodes are hydrogen and oxygen. Explain why [4]

Answer 10

Hydrogen (H+) and sodium (Na+) ions are attracted to cathode, hydroxide (OH−) ions and sulfate (SO42−) ions are attracted to the anode; [1 mark]
Reason:
The ions are attracted to the oppositely charged electrode; [1 mark]
2 hydrogen ions / 2H+ accept 2e- to form a hydrogen molecule / H2; [1 mark]
4 hydroxide ions / 4OH− lose 4e- to form an oxygen molecule / O2; [1 mark]
[Total: 4 marks]

Question 11

The following are the results obtained from an electrolysis experiment when copper sulfate solution was electrolysed for 10 minutes.
Anode: -0.81g change in mass
Cathode: +0.78g change in mass
Explain, in terms of ions, the changes in mass shown above. [3]

Answer 11

• at anode, copper / atoms {lose electrons/ oxidised} / (copper) ions leave anode (cause mass loss) [1]
• (copper) ions (in solution) move to the cathode [1]
• at cathode (copper) ions {gain electrons/ reduced} (-cause mass gain) [1]

Question 12

Calcium nitrate and calcium carbonate are both ionic compounds
Calcium nitrate mixed with water behaves as an electrolyte.
Calcium carbonate mixed with water does not behave as an electrolyte.
Explain, in terms of solubility and movement of ions, this difference in behaviour. [2]

Answer 12

• (calcium) nitrate {is soluble/ dissolves}, (calcium) carbonate {is insoluble/ doesn’t dissolve}
• so ions {free to move in solution/ not free in solid}

Question 13

In the electrolysis of sodium chloride solution, bubbles of a colourless gas form at the
cathode.
This gas, when mixed with air, burns with a squeaky pop.
Explain how this gas is formed at the cathode. [2]

Answer 13

• hydrogen ions attracted to cathode/ negatively charged electrode [1]
• (two) hydrogen ions {gain (two) electrons/ are reduced/ form hydrogen molecules}/ correct half equation [1]

Question 14

State what could be added into the circuit to show a current is flowing during electrolysis. [1]

Answer 14

light bulb / ammeter/ lamp [1]

Question 15

Explain how lubricating the chain with oil prevents corrosion of the steel chain. [2]

Answer 15

• {air/oxygen} excluded / {water/moisture} excluded / oil acts as a barrier (1)
• {air/oxygen} and {water/moisture/damp conditions} both needed (for iron to rust / corrosion) (1)

Question 16

Excess solid nickel carbonate is added to dilute sulfuric acid in a beaker.
Nickel sulfate is formed in solution.
Describe how a sample of pure, dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker. [3]

Answer 16

• filter (1)
  and two in a logical order from
• crystallisation (1)
• heat solution (to concentrate) (1)
• allow to cool (1)
• dry crystals between filter papers (1)

Question 17

Aluminium cannot be extracted by heating its oxide with carbon.
Aluminium has to be extracted from its oxide by electrolysis.
Explain why. [2]

Answer 17

• aluminium is high in reactivity / aluminium oxide is (very) stable (1)
• aluminium (oxide) cannot be reduced by carbon (1)

Question 18

An experiment is planned to record the change in pH as a powdered base is added to 50cm3 of dilute hydrochloric acid. Explain why, in terms of particles present, the pH increases during the experiment. [2]

Answer 18

In terms of the particles present, the pH increases during the experiment because:
The hydrogen ions are reacted / neutralised
OR
H+ + OH– → H2O; [1 mark]
So, the concentration of hydrogen ions / H+ decreases
OR
So, the concentration of hydroxide ions / OH– increases; [1 mark]

Question 18

In recent years, researchers have been investigating alternative methods of extracting metals from soils.
Researchers have found that growing certain plants in appropriate areas can result in the phytoextraction of copper.
Describe how growing plants can result in the phytoextraction of copper [2]

Answer 18

• plants absorb {copper/metal} (ions) from the {soil/ores} / plants concentrate copper ions (1)
• plants (harvested and) burned (to leave copper/metal compound) (1)

Question 19

During an experiment, the pH of a solution changes from 2 to 10. If phenophthalein indicator is added at the beginning of the experiment, a colour change happens. State the colour change that occurs. [1]

Answer 19

Colourless to Pink [1]

Question 20

State and Explain how the pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid [4]

Answer 20

The pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid by:
Increases pH; [1 mark]
Until pH above 7; [1 mark]
And an explanation linking:
REACTION
{Magnesium hydroxide / base / alkali / OH- ions} {reacts with / neutralises} {the acid / the H+ ions}; [1 mark]
IONS REMAINING
So the hydrogen ions concentration is reduced / all hydrogen ions reacted / there is an excess of hydroxide ions; [1 mark]

Question 21

Using different reactants, a solution of copper sulfate was prepared
Describe what should be done to obtain copper sulfate crystals from this copper sulfate solution [2]

Answer 21

Heat solution (to evaporate water and concentrate the salt solution); [1 mark]
Leave to cool / in a warm place / on window sill / for several days; [1 mark]

Question 22

Explain what is a weak acid [2]

Answer 22

• partially {dissociated / ionised} [1]
• { concentration of H+ ions lower / fewer H+ ions} than expected [1]

Question 23

During an experiment, the pH of a solution changes from 2 to 10, as a base is added to an acid.
Explain, in terms of particles present, why the pH increases during the experiment. [2]

Answer 23

• {hydrogen ions/H+ ions}{reacted / neutralised} [1]
• {concentration falls/fewer} H+/{concentration rises/more} OH- [1]

Question 24

Describe how the pH of a mixture is determined when a drop of it is placed on universal indicator paper [2]

Answer 24

• (observe/look at) colour produced on universal indicator paper [1]
• compare to pH chart [1]

Question 25

Describe how soluble salts can be made [3]

Answer 25

• Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates (1 mark)
• The solid is added to the acid until no more reacts (1 mark)
• The excess solid is filtered off to produce to solution of the salt (1 mark)

Question 26

A student carries out two experiments that investigate rates of reaction, with the variables temperature and pressure. In the second experiment, she changes both variables. Explain why it is not possible to predict the rate of experiment 2 as compared to experiment 1. [3]

Answer 26

The decrease in temperature will cause a decrease in the rate of reaction; [1 mark]
The increase in pressure will cause an increase in the rate of reaction; [1 mark]
Because the changes have opposite effects on the rate it is not possible which has the greater effect; [1 mark]

Question 27

Explain in terms of bond breaking and bond making, why some reactions are exothermic [3]

Answer 27

Breaking bonds needs energy / is endothermic; 1 [mark]
Making bonds releases energy / is exothermic; 1 [mark]
(A reaction is exothermic if) more energy is given out / released than taken in; [1 mark]

Question 28

Explain why, in terms of bond breaking and making, the combustion of methanol is an exothermic reaction [1]

Answer 28

More energy is released when the bonds are formed than the energy required to break the bonds
OR
Less energy is required to break the bonds than is released when the bonds are formed; [1 mark]

Question 29

In the electrolysis of sodium chloride solution, bubbles of a colourless gas form at
the cathode.
This gas, when mixed with air, burns with a squeaky pop. Explain how this gas is formed at the cathode. [2]

Answer 29

• hydrogen ions attracted to cathode/negatively
  charged electrode (1)
• (two) hydrogen ions {gain (two) electrons /are
  reduced / form hydrogen molecules} / correct half
  equation (2H+ + 2e(-) → H2) (1)

Question 30

Give one advantage of using a hydrogen-oxygen fuel cell, rather than using a chemical cell, to power a vehicle. [1]

Answer 30

A constant voltage

Question 31

Name the half equation that occurs at the one of the electrodes of a hydrogen-oxygen fuel cell [2]

Answer 31

O2 + 4H+ + 4e(-)
→ 2H2O (2)

Question 32

When hydrogen is removed from an alkane, an alkene is formed. This is an example of a dehydrogenation reaction.
Under certain conditions the dehydrogenation of propane forms propene and a dynamic equilibrium is reached.
State what is meant by dynamic in this context. [1]

Answer 32

both forward and back(ward) reactions take place at same time

Question 33

The titration was repeated to obtain a mean volume of dilute sulfuric acid required to neutralise the 25.0cm3 of ammonia solution.
The volumes of the two solutions were measured accurately.
Explain two other practical steps that should be used in the titration to ensure that an accurate titre volume is obtained. [4]

Answer 33

• use of white tile (1)
• easier to see precisely when indicator changes colour (1)
• (near to end point) {add (acid) slowly / in small quantities each time} (1)
• easier to stop excess acid being added (when indicator changes colour) (1)
• swirl flask when adding acid (1)
• ensures complete mixing of both reactants (1)
• touch tip of burette on inside wall of flask and/or rinse walls of flask (1)
• ensures all acid takes part in reaction (1)
• rinse burette (with acid)/ pipette (with ammonia)/flask (with water) beforehand (1)
• no impurities to affect result (1)
  ▪ remove funnel from burette (1)
  ▪ to stop any extra drop of acid falling into burette (1)

Question 33

Copper is low down in the reactivity series and can be obtained from copper oxide.
Devise a simple method to obtain a sample of copper from copper oxide in the laboratory [2]

Answer 33

• mix copper oxide with {carbon / powdered charcoal}
  (in a suitable container) (1)
• heat (with carbon) (strongly until no further change) (1)
  OR
• react copper oxide with dilute {sulfuric / hydrochloric} acid (1)
• electrolyse the solution formed (1)
  OR
• pass hydrogen (or methane) (1)
• over heated copper oxide (1)

Question 34

Before the electrolysis is carried out, the mass of each electrode is determined.
Explain what should be done to the copper electrodes before their masses are determined.[2]

Answer 34

• (electrodes) cleaned (using emery paper) (or similar) (1)
• to remove {surface oxide / grease / impurities} (1)