Question
This question is about zinc and its compounds.
(a) Zinc is extracted from its ore which is mainly zinc sulfide, ZnS.
The steps for this extraction are shown.
step 1 Zinc sulfide is converted into zinc oxide.
step 2 The zinc oxide is then reduced to zinc in a furnace. The zinc formed becomes a gas.
step 3 The zinc gas is cooled to form molten zinc.
(i) Name the ore of zinc, which is mainly zinc sulfide. [1]
(ii) Describe how zinc sulfide is converted into zinc oxide in step 1.[1]
(iii) Name the reducing agent used in step 2. [1]
(iv) Explain why the zinc forms a gas in step 2 inside the furnace.[1]
(v) State the name of the physical change occurring when zinc gas is converted into molten zinc.[1]
(b) Zinc sulfate crystals, ZnSO4•7H2O, are hydrated.
Zinc sulfate crystals are made by reacting zinc carbonate with dilute sulfuric acid.
The equation for the overall process is shown.
ZnCO3 + H2SO4 + 6H2O → ZnSO4•7H2O + CO2
step 1 Large pieces of solid zinc carbonate are added to dilute sulfuric acid until the zinc carbonate is in excess. This forms aqueous zinc sulfate.
step 2 The excess zinc carbonate is separated from the aqueous zinc sulfate.
step 3 The aqueous zinc sulfate is heated until a saturated solution is formed.
step 4 The saturated solution is allowed to cool and crystallise.
step 5 The crystals are removed and dried.
(i) In step 1, zinc carbonate is in excess when no more zinc carbonate dissolves.
State one other observation that indicates the zinc carbonate is in excess in step 1.[1]
(ii) Name a different substance, other than zinc carbonate, that can be added to dilute sulfuric acid to produce aqueous zinc sulfate in step 1.[1]
(iii) Step 1 is repeated using powdered zinc carbonate instead of large pieces.
All other conditions are kept the same.
The rate of reaction increases.
Give a reason why the rate of reaction increases. Explain your answer in terms of particles. [2]
(iv) Suggest what is observed when the solution is saturated in step 3.[1]
(v) The formula of zinc sulfate crystals is ZnSO4•7H2O.
Give the formula of the solid formed if the crystals are heated to dryness in step 3. [1] [Total: 11]
Answer/Explanation
Ans:
6(a)(i) zinc blende
6(a)(ii) heat( zinc sulfide) strongly in air / roast in air
6(a)(iii) carbon or carbon monoxide
6(a)(iv) the temperature in the furnace is above or higher than the boiling point of zinc
OR
the boiling point of zinc is below or less than the temperature of the furnace
6(a)(v) condensation / condensing / condense
6(b)(i) no bubbles
or
no fizzing
or
no effervescence
6(b)(ii) zinc / zinc oxide / zinc hydroxide
6(b)(iii) (powder has) larger surface area OR lumps have smaller surface area (1)
(powder has) more collisions per unit time / more collision frequency
OR
lumps have fewer collisions per unit time / less collision frequency (1)
6(b)(iv) crystals (form on glass rod or microscope slide)
6(b)(v) ZnSO4
Question
This question is about iron.
(a) Iron is extracted from its main ore in a blast furnace.
(i) Name the main ore of iron used in the blast furnace.
(ii) Name the substance that enters the blast furnace at A.
(iii) Name the substance that leaves the blast furnace at B.
(iv) Give two reasons for using coke in the blast furnace.
1 …………………………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………………………
(b) Another ore of iron is iron pyrites, \(FeS_2\). Iron pyrites contains the positive ion, \(Fe^{2+}\).
Deduce the formula of the negative ion in \(FeS_2\).
(c) Iron is a transition element.
A list of properties of iron is shown.
● Iron is a good conductor of electricity.
● Iron forms soluble salts.
● Iron forms coloured compounds.
● Iron has variable oxidation states.
● Iron acts as a catalyst.
● Iron forms a basic oxide.
(i) Give two properties from the list in which iron differs from Group I elements.
1 …………………………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………………………
(ii) Give two properties from the list in which iron is similar to Group I elements.
1 …………………………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………………………
(d) Steel consists mainly of iron.
Iron forms rust when it reacts with water and oxygen.
Magnesium blocks can be attached to the bottom of steel boats. The magnesium does not
completely cover the steel.
(i) Explain how the magnesium blocks prevent iron from rusting.
(ii) Explain why replacing the magnesium blocks with copper blocks will not prevent the
bottom of the boat from rusting.
Answer/Explanation
Answer:
(a) (i) hematite
(ii) air
(iii) slag / calcium silicate
(iv) any two from:
• (coke)
releases heat (when it reacts with oxygen or reacts in air)
OR (acts as a) fuel
OR increases temperature (in the furnace) / heats (the furnace)
OR source of energy
• (coke or carbon monoxide)
reduces iron oxide
OR is a reducing agent
OR converts iron oxide to iron /
removes oxygen from iron oxide
• (coke)
reacts with oxygen to form carbon monoxide
OR reacts with carbon dioxide to form carbon monoxide
(b) \(S_2^{2-}\) or S-
(c) (i) any two from:
• (iron forms) coloured compounds
• (iron has) variable oxidation states
• (iron acts as a) catalyst
(ii) any two from:
• (iron is) good conductor of electricity
• (iron) forms a basic oxide
• (iron salts are) soluble (in water)
(d) (i) magnesium is more reactive than iron / steel ORA (1)
iron is not oxidised
OR
iron does not lose electrons
OR
magnesium loses electrons more easily than or in preference (to iron) ORA
OR
magnesium is oxidised more easily or reacts with oxygen more easily or corrodes more easily or in preference (to iron)
ORA (1)
(ii) copper is less reactive than iron / copper is lower in the reactivity series than iron ORA
Question
Some elements are shown in the order they appear in the reactivity series. The most reactive element is at the top.
sodium
calcium
magnesium
aluminium
zinc
iron
hydrogen
copper
(a) Answer the questions using the list of elements. Each element may be used once, more than once or not at all.
Identify:
(i) a non-metal
(ii) a metal which is stored under oil
(iii) the main component of steel
(iv) a metal with three electrons in the outer shell of its atoms
(v) a metal found in brass
(vi) a metal that forms chlorides of the type \(XCl_2\) and \(XCl_3\).
(b) Name the main ores of:
(i) zinc ……………………………………………………………………………………………………………….
(ii) aluminium. ……………………………………………………………………………………………………..
(c) In an experiment, a sample of aluminium appeared less reactive than expected.
Explain why.
(d) Name two metals from the list which are extracted by reduction of their ores using carbon.
1 ……………………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………………….
(e) When zinc granules are added to aqueous copper(II) sulfate, a reaction occurs. During the
reaction, a red-pink solid is formed and the solution becomes colourless.
(i) Name the red-pink solid.
(ii) Name the colourless solution.
(iii) Explain, in terms of particles, why the rate of this reaction increases when the temperature
is increased.
(iv) Suggest two other ways of increasing the rate of this reaction.
1 …………………………………………………………………………………………………………………………
2 …………………………………………………………………………………………………………………………
Answer/Explanation
Answer:
(a) (i) hydrogen
(ii) sodium
(iii) iron
(iv) aluminium
(v) zinc or copper
(vi) iron
(b) (i) zinc blende
(ii) bauxite
(c) protective oxide layer
(d) Any 2 from 3
• zinc
• iron
• copper
(e) (i) copper
(ii) zinc sulfate
(iii)
M1 particles have more energy
M2 More collisions (between particles) occur per second / per unit time
M3 A greater percentage / proportion / fraction of collisions (of particles) are successful / have energy above activation
energy / have energy equal to activation energy
(iv) Any 2 from 3:
• use a catalyst
• use smaller granules
• increase concentration