1.
State what is meant by an acid.
[1 mark]
- a substance that produces H⁺ ions in water / proton donor
JD SCIENCE
Chemical changes
Indicative marking points. Award marks for equivalent scientific or mathematical wording. Do not issue this sheet with the student worksheet.
2.
State what is meant by an alkali.
[1 mark]
- a soluble base that produces OH⁻ ions
3.
State what is meant by a salt.
[1 mark]
- a compound formed when H⁺ in an acid is replaced by a metal ion or ammonium
4.
State what is meant by electrolysis.
[1 mark]
- breaking down an ionic compound using electricity
5.
State what is meant by reduction.
[1 mark]
- gain of electrons / loss of oxygen
6.
State what is meant by oxidation.
[1 mark]
- loss of electrons / gain of oxygen
7.
State what is meant by the reactivity series.
[1 mark]
- metals in order of reactivity
8.
State what is meant by a displacement reaction.
[1 mark]
- a more reactive metal displaces a less reactive metal from a compound
9.
State what is meant by neutralisation.
[1 mark]
- acid + base → salt + water
10.
State what is meant by the extraction of iron.
[1 mark]
- reduction of iron oxide with carbon in a blast furnace
11.
Devon is asked about an acid in a Edexcel Chemistry paper.
(a) [2 marks]
- pH less than 7
(b) [3 marks]
- why a strong acid has a lower pH than a weak acid of the same concentration
12.
Devon is asked about an alkali in a Edexcel Chemistry paper.
(a) [2 marks]
- pH more than 7
(b) [3 marks]
- why acids and alkalis neutralise
13.
Devon is asked about a salt in a Edexcel Chemistry paper.
(a) [2 marks]
- e.g. NaCl from HCl
(b) [3 marks]
- why the salt name depends on the acid
14.
Devon is asked about electrolysis in a Edexcel Chemistry paper.
(a) [2 marks]
- ions must be free to move
(b) [3 marks]
- why a solid ionic compound does not conduct
15.
Devon is asked about reduction in a Edexcel Chemistry paper.
(a) [2 marks]
- at the cathode in electrolysis
(b) [3 marks]
- why aluminium is extracted by electrolysis not reduction with carbon
16.
Devon is asked about oxidation in a Edexcel Chemistry paper.
(a) [2 marks]
- at the anode in electrolysis
(b) [3 marks]
- why OIL RIG is useful
17.
HCl + NaOH → NaCl + H₂O. 25.0 cm³ of 0.100 mol/dm³ HCl is neutralised. Moles of HCl?
[3 marks]
- cV
- Final answer: 0.00250 mol
18.
If the NaOH volume was 20.0 cm³, what is its concentration?
[3 marks]
- same moles
- Final answer: 0.125 mol/dm³
19.
pH of 0.010 mol/dm³ strong monoprotic acid (if [H⁺]=0.010).
[3 marks]
- pH = −log[H⁺] if on spec; else state pH is low
- Final answer: 2
20.
Mass of Cu from Cu²⁺ + 2e⁻ → Cu if 0.25 mol of electrons flow.
[3 marks]
- 2 mol e⁻ per mol Cu
- Final answer: 8 g (0.125 mol × 63.5)
21.
A metal oxide is 80% metal by mass. Mass of metal in 50 g of oxide?
[3 marks]
- Final answer: 40 g
22.
In 2Al + Fe₂O₃ → Al₂O₃ + 2Fe, moles of Al needed for 0.5 mol Fe₂O₃?
[3 marks]
- ratio 2:1
- Final answer: 1 mol
23.
Devon carries out making a soluble salt from an acid and a metal oxide or carbonate. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: acid / base
- Dependent: crystals formed
(b) [2 marks]
- filter off excess base
- so the test is fair / only one variable is changed
(c) [2 marks]
- not using excess base so acid remains
24.
Devon carries out electrolysis of aqueous copper chloride or sodium chloride (demonstration if chlorine). This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: electrolyte
- Dependent: products at electrodes
(b) [2 marks]
- same current time
- so the test is fair / only one variable is changed
(c) [2 marks]
- wrong electrode identification
25.
Devon carries out displacement reactions of metals with metal salt solutions. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: metal
- Dependent: whether a coating / colour change occurs
(b) [2 marks]
- same concentration of salt
- so the test is fair / only one variable is changed
(c) [2 marks]
- dirty metal surface
26.
Devon carries out pH measurement of acids of different concentration. This is a typical Edexcel required-practical style question.
(a) [2 marks]
- Independent: concentration
- Dependent: pH
(b) [2 marks]
- same acid type
- so the test is fair / only one variable is changed
(c) [2 marks]
- unwashed pH probe
27.
Compare a strong acid with a weak acid.
[4 marks]
- strong: fully ionised
- weak: partially ionised
28.
Compare reduction with carbon with electrolysis.
[4 marks]
- carbon: cheaper for less reactive metals
- electrolysis: needed for more reactive metals, expensive
29.
Compare the cathode with the anode.
[4 marks]
- cathode: reduction, negative
- anode: oxidation, positive
30.
Compare an acid + a metal with an acid + a carbonate.
[4 marks]
- metal: salt + hydrogen
- carbonate: salt + water + carbon dioxide
31.
Apply your knowledge of the reactivity series to this situation: copper is less reactive
[3 marks]
- copper is less reactive
32.
Apply your knowledge of a displacement reaction to this situation: more reactive element takes the oxygen
[3 marks]
- more reactive element takes the oxygen