Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2018 Winter Zone 3

Answer the following questions using only the substances in the list. Each substance may be used once, more than once or not at all.

ammonia   bauxite   carbon dioxide   carbon monoxide
hematite   oxygen   sodium chloride   sulfur dioxide

State which substance is:
(a) an element ............................................................................................................................. [1]
(b) an ore of iron ........................................................................................................................ [1]
(c) used to bleach wood pulp ........................................................................................................ [1]
(d) used to manufacture fertilisers .................................................................................................. [1]
(e) a toxic gas produced during the incomplete combustion of hydrocarbons
............................................................................................................................. [1]
(f) an ionic compound ................................................................................................................. [1]
(g) a reactant in photosynthesis .................................................................................................... [1]
(h) a product of photosynthesis. .................................................................................................... [1]

This question is about electrolysis.
(a) (i) What is meant by the term *electrolysis*?
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(ii) Name the type of particle responsible for the conduction of electricity during electrolysis in:
the metal wires ........................................................
the electrolyte ........................................................
[4]
(b) The table gives information about the products of the electrolysis of two electrolytes. Platinum electrodes are used in each case.
(i) Give *two* reasons why platinum is suitable to use as an electrode.
1 ........................................................
2 ........................................................
[2]
(ii) Complete the table.

(a) Calculate the relative formula mass, $M_r$, of $Cu_2FeSnS_4$.

$M_r$ of $Cu_2FeSnS_4$ = .................................

(b) The $M_r$ of $SnO_2$ is 151.

Calculate the percentage of tin by mass in $SnO_2$.

percentage of tin by mass in $SnO_2$ = .................................

(c) The percentage of tin by mass in $Cu_2FeSnS_4$ is 27.6%.

Use this information and your answer to (b) to suggest whether it would be better to extract tin from $SnO_2$ or $Cu_2FeSnS_4$.
Explain your answer.
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(d) Tin can be extracted by heating tin(IV) oxide with carbon. Carbon monoxide is the other product.
Write a chemical equation for this reaction.
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(e) The position of tin in the reactivity series is shown.

iron most reactive
tin ↑
copper least reactive

A student added iron to a solution containing $Sn^{2+}$ ions.
The student then separately added tin to a solution containing $Cu^{2+}$ ions.
Complete the ionic equations. If there is no reaction write 'no reaction'.

$Fe + Sn^{2+} \rightarrow$ .............................................................
$Sn + Cu^{2+} \rightarrow$ .............................................................

(f) Copper(II) nitrate, $Cu(NO_3)_2$, decomposes when it is heated. The only solid product is copper(II) oxide, CuO. There are two gaseous products. One of the gaseous products is oxygen.

(i) Describe a test for oxygen.
test ....................................................................................................
result ....................................................................................................
[2]

(ii) Name the other gaseous product. Describe its appearance.
name ...................................................................................................
appearance ..........................................................................................
[2]

(iii) Write a chemical equation for the thermal decomposition of copper(II) nitrate.
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(g) Iron does not rust when it is completely coated with zinc. When the zinc is scratched, the iron still does not rust.

(i) Explain why the iron does not rust when it is completely coated with zinc.
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(ii) Explain why the iron still does not rust when the zinc is scratched.
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(a) Dilute sulfuric acid and aqueous potassium hydroxide can be used to make potassium sulfate crystals using a method that includes titration.

A student titrated 25.0 cm³ of 0.0500 mol/dm³ aqueous potassium hydroxide with dilute sulfuric acid in the presence of an indicator. The volume of dilute sulfuric acid needed to neutralise the aqueous potassium hydroxide was 20.0 cm³.
The equation for the reaction is shown.
$$\text{H}_2\text{SO}_4 + 2\text{KOH} \rightarrow \text{K}_2\text{SO}_4 + 2\text{H}_2\text{O}$$
Determine the concentration of the dilute sulfuric acid.
• Calculate the number of moles of aqueous potassium hydroxide used.
.............................. mol

• Calculate the number of moles of dilute sulfuric acid needed to neutralise the aqueous potassium hydroxide.
.............................. mol

• Calculate the concentration of the dilute sulfuric acid.
.............................. mol/dm³

(b) After the titration has been completed, the conical flask contains an aqueous solution of potassium sulfate and some of the dissolved indicator.
Describe how to prepare a pure, dry sample of potassium sulfate crystals from new solutions of dilute sulfuric acid and aqueous potassium hydroxide of the same concentrations as used in the titration. Include a series of key steps in your answer.
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(c) Potassium hydrogensulfate, KHSO₄, is an acid salt. It dissolves in water to produce an aqueous solution, X, containing K⁺, H⁺ and SO₄^2– ions.
Describe what you would see when the following experiments are done.
(i) Magnesium ribbon is added to an excess of solution X.
..........................................................................................................................................................
......................................................................................................................................................... [2]

(ii) A flame test is done on solution X.
.......................................................................................................................................................... [1]

(iii) An aqueous solution containing barium ions is added to solution X.
.......................................................................................................................................................... [1]

(d) Dilute sulfuric acid reacts with bases, metals and carbonates.
Write chemical equations for the reaction of dilute sulfuric acid with each of the following:
(i) magnesium hydroxide
......................................................................................................................................................... [2]

(ii) zinc
......................................................................................................................................................... [2]

(iii) sodium carbonate
......................................................................................................................................................... [2]

A student investigates the rate of reaction between lumps of calcium carbonate and dilute hydrochloric acid using the apparatus shown.

$$\text{CaCO}_3(s) + 2\text{HCl}(aq) \rightarrow \text{CaCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$$

The calcium carbonate was in excess.

[Image of apparatus]

(a) Which measurements should the student make during the reaction to determine the rate of reaction?
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[2]

(b) What happens to the rate of reaction as the reaction proceeds? Explain your answer.
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[3]

(c) The student repeated the experiment at a higher temperature. All other conditions were kept the same. The student found that the rate of reaction increased.
Explain, in terms of collisions, why the rate of reaction increased.
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[4]

(d) Apart from using a higher temperature, suggest two other methods of increasing the rate of this reaction.
1 .................................................................................................................................................
2 .................................................................................................................................................
[2]

(a) Ethanol can be manufactured by fermentation and by hydration.
(i) Describe these two processes of ethanol manufacture.
In each case you should:
• identify the reactants
• give the reaction conditions
• write a chemical equation for the reaction which produces ethanol.
fermentation ...............................................................................................................
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hydration ..................................................................................................................
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[6]
(ii) Give two advantages of ethanol manufacture by fermentation compared to by hydration.
1 .................................................................................................................................
2 .................................................................................................................................
[2]
(iii) State two major uses of ethanol.
1 .................................................................................................................................
2 .................................................................................................................................
[2]

(b) The structures of some polymers are shown.
A —O—□—O—□—O—□—
B —O—□□—O—□□—O—
C —□—O—□—O—□□—
D —□—N—□—N—□—
| | H
E —CH_2—CH(CH_3)—CH_2—CH(CH_3)—CH_2—
Answer the following questions about these polymers.
Each polymer may be used once, more than once or not at all.
State which polymer, A, B, C, D or E, represents:
(i) an addition polymer ......................................................................................... [1]
(ii) a protein ........................................................................................................ [1]
(iii) a polyester made from only one monomer .................................................... [1]
(iv) Terylene ......................................................................................................... [1]
(v) a complex carbohydrate ................................................................................ [1]