Question
Sodium is manufactured by electrolysis.
(a) Explain why sodium is manufactured by electrolysis and not by reduction with carbon.
(b) The diagram shows the equipment for the production of sodium.
(i) The anode is inert.
Suggest a suitable substance that can be used for the anode.
(ii) Label the anode on the diagram.
(iii) Describe, by reference to the diagram, how you know that sodium is less dense than
molten sodium chloride.
(c) When concentrated aqueous sodium chloride is electrolysed, gases are produced at each electrode.
State the names of the products and give the observations at each electrode.
product at the negative electrode ………………………………………………………………………………….
observations at the negative electrode …………………………………………………………………………..
product at the positive electrode ……………………………………………………………………………………
observations at the positive electrode ……………………………………………………………………………
(d) Give two ways in which the physical properties of sodium are different from the physical properties of transition elements.
1 ……………………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………………….
(e) The symbol equation for the production of sodium hydride is shown.
\(2Na + H_2 → 2NaH\)
(i) Write a word equation for this reaction.
(ii) Suggest why the hydrogen must be dry.
(iii) Sodium hydride reduces iron(III) oxide to iron.
\(Fe2O_3 + 3NaH → 2Fe + 3NaOH\)
Explain how this equation shows that iron(III) oxide is reduced.
(f) State the colour observed in the flame test for sodium.
Answer/Explanation
Answer:
(a) sodium is too reactive / sodium is high in the electrochemical series / it takes too high a temperature to extract sodium using
carbon
(b) (i) graphite / platinum
(ii) ‘square’ in middle of diagram labelled anode
(iii) the sodium floats on top of the sodium chloride
(c) negative electrode:
hydrogen (1)
bubbles / fizzing / colourless gas (1)
positive electrode:
chlorine (1)
bubbles / fizzing / green gas / yellow-green gas (1)
(d) 1 mark each for any 2 of:
• sodium is soft / not strong / more malleable / more ductile
• sodium has low density
• sodium has (relatively) low melting point
(e) (i) sodium + hydrogen → sodium hydride
(ii) so that sodium does not react with water / sodium reacts with water
(iii) the iron oxide has lost oxygen
(f) yellow (1)
Question
This question is about metals and compounds of metals.
(a) Identify two correct statements about transition elements. Tick two boxes.
(b) The table compares the ease of reduction of some metal oxides with carbon.
Put the four metals in order of their reactivity.
Put the least reactive metal first.
(c) Crystals of copper(II) sulfate, $\mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}$, can be prepared by heating excess copper(II) oxide powder with dilute sulfuric acid.
(i) Describe how to prepare a sample of pure dry copper(II) sulfate crystals after the reaction is complete.
In your answer describe how to:
- remove the excess copper(II) oxide from the reaction mixture
- crystallise the copper(II) sulfate
- dry the crystals. [4]
(ii) Identify the word that best describes copper(II) sulfate.
Draw a circle around the correct answer.
acid $\bigcirc$
halogen $\bigcirc$
polymer $\bigcirc$
salt $\bigcirc$ [1]
(d) A few drops of water are added to a sample of solid anhydrous copper(II) sulfate, $\mathrm{CuSO}_4$.
(i) The reaction is reversible.
$$
\mathrm{CuSO}_4+5 \mathrm{H}_2 \mathrm{O} \quad\square\quad \mathrm{CuSO}_4 \cdot 5 \mathrm{H}_2 \mathrm{O}
$$
Draw in the box, the sign for a reversible reaction. [1]
(ii) State the colour change observed when water is added to anhydrous copper(II) sulfate.
from —————– to ——————————– [2] [Total: 12]
▶️Answer/Explanation
Ans:
(a)$2^{\text {nd }}$ box down ticked (have high densities) (1)
$4^{\text {th }}$ box down ticked (high melting points) (1)
(b) copper<cobalt<manganese<magnesium (2)
If 2 marks not scored one mark for one consecutive pair reversed / all reversed
(c)(i) one mark each for any four of:
• filter (off copper oxide)
• warm (or heat or evaporate) filtrate to point of crystallisation / warm filtrate to form saturated solution / heat filtrate until
crystals start to form
• filter off crystals / pick out crystals
• wash crystals with cold water / wash crystals with (organic) solvent
• dry crystals with filter paper
(c)(ii) salt
(d)(i) ⇌
8(d)(ii) white (1)
(to) blue (1)
Question
Catalysts increase the rate of chemical reactions.
(a) Name the type of metals often used as catalysts. [1]
(b) A student investigated the reaction of zinc powder with excess dilute hydrochloric acid in the absence of a catalyst.
$
\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_2+\mathrm{H}_2
$
The student measured the volume of hydrogen gas produced at 10 second intervals. The graph shows the results.
Answer these questions using information from the graph.
(i) Deduce the volume of hydrogen produced in the first 25 seconds of the experiment.
volume = ………………………… cm3[1]
(ii) Explain why no more hydrogen is produced after 50 seconds. ……………………………………………………………………………………………………………………… [1]
(iii) The experiment is repeated using a catalyst.
Draw a line on the grid to show how the volume of hydrogen changes with time when a catalyst is used.
All other conditions stay the same. [2]
(iv) Describe what effect the following changes have on the rate of the reaction.
- The concentration of hydrochloric acid is decreased.
All other conditions stay the same.
- Large pieces of zinc are used.
All other conditions stay the same. [5]
(c) (i) Describe a test for hydrogen.
test………………………….
result……………………………….. [3]
(ii) State one use of hydrogen. [1] [Total: 10]
▶️Answer/Explanation
Ans:
(a) transition (elements)
(b)(i) $70 \mathrm{~cm}^3$
(b)(ii) the reaction has finished / all the zinc has been used up 1
(b)(iii) Line starts at 0, 0 and steeper gradient (1)
Line levels out at 96 cm3 hydrogen and before the line already on the grid (1)
(b)(iv) concentration: (rate) decreases / gets slower (1)
particle size: (rate) decreases / gets slower (1)
(c)(i) lighted splint (1)
pops / explodes (1)
(c)(ii) fuel