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

The following are the symbols and formulae of some elements and compounds.

Ar Ca(OH)_2 Cl_2 CO_2 Cu Fe SO_2 V_2O_5

Answer the following questions using only the elements or compounds in the list.
Each element or compound may be used once, more than once or not at all.

State which element or compound is used:

(a) to kill bacteria in drinking water ............................................................ [1]
(b) as a food preservative ............................................................ [1]
(c) as an electrical conductor in cables ............................................................ [1]
(d) as an inert atmosphere in lamps ............................................................ [1]
(e) to neutralise excess acidity in soil ............................................................ [1]
(f) as a catalyst in the Contact process. ............................................................ [1]

(a) $^{29}Al$ is a radioactive isotope of aluminium. The only non-radioactive isotope of aluminium is $^{27}Al$.

(i) Describe, in terms of protons, neutrons and electrons, how the isotopes $^{29}Al$ and $^{27}Al$ are similar and how they are different.

how they are similar .........................................................................................................................
how they are different ....................................................................................................................... [2]

(ii) Complete the table to show the number of nucleons, neutrons and electrons in an $^{27}_{13}Al^{3+}$ ion.



[3]

(b) Aluminium is extracted from its ore by electrolysis.

(i) Name the main ore of aluminium.
.................................................................................................................................................... [1]

(ii) Why is aluminium not extracted from its ore by reduction with carbon?
.................................................................................................................................................... [1]

(iii) The main ore of aluminium contains aluminium oxide. Aluminium oxide is dissolved in molten cryolite before it is electrolysed.
Give two reasons, other than cost, why cryolite is used.
1 ................................................................................................................................................
2 ................................................................................................................................................ [2]

(iv) The reaction at the anode during the extraction of aluminium by electrolysis is shown.
$$2O^{2-} \longrightarrow O_{2} + 4e^{-}$$
Is this process oxidation or reduction?
Give a reason for your answer.
.................................................................................................................................................... [1]

(v) During the extraction of aluminium by electrolysis, carbon dioxide is formed at the anode.
Explain how carbon dioxide is formed at the anode.
....................................................................................................................................................
.................................................................................................................................................... [2]

(c) When a piece of zinc metal is added to copper(II) sulfate solution there is an immediate reaction.

$$Zn + CuSO_{4} \longrightarrow ZnSO_{4} + Cu$$

When a piece of aluminium metal is added to copper(II) sulfate solution the initial reaction is very slow.

(i) Explain why zinc metal reacts with copper(II) sulfate.
.................................................................................................................................................... [1]

(ii) What type of reaction is this?
.................................................................................................................................................... [1]

(iii) Explain why the initial reaction between aluminium metal and copper(II) sulfate is very slow.
.................................................................................................................................................... [1]

Cobalt is a transition element. Potassium is in Group I of the Periodic Table.

(a) State one physical property that is similar for cobalt and potassium.
................................................................................................................................................ [1]

(b) (i) State one physical property that is different for cobalt and potassium.
................................................................................................................................................ [1]

(ii) Describe how the physical property given in (b)(i) is different for cobalt compared to potassium.
................................................................................................................................................ [1]

(c) When a small piece of potassium is added to cold water, the potassium floats and disappears as it reacts.
Give two other observations that would be made when a small piece of potassium is added to cold water.
1 ...............................................................................................................................................
2 ............................................................................................................................................... [2]

(d) Cobalt reacts with dilute hydrochloric acid to make the salt cobalt(II) chloride. Bubbles of hydrogen gas are produced.

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

(ii) The rate of reaction of cobalt with dilute hydrochloric acid can be made faster by heating the acid or by increasing its concentration.
State one other way to make the rate of reaction faster.
................................................................................................................................................ [1]

(iii) Use collision theory to explain how heating the dilute hydrochloric acid makes the rate of reaction faster.
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................ [3]

(e) When cobalt(II) chloride is added to water an equilibrium is established.
\[ [\text{CoCl}_4]^{2-} + 6\text{H}_2\text{O} \rightleftharpoons [\text{Co(H}_2\text{O)}_6]^{2+} + 4\text{Cl}^- \]
blue pink

(i) A student adds water to a blue solution containing \([\text{CoCl}_4]^{2-}\) ions.
Describe what the student observes. Give a reason for your answer in terms of the position of the equilibrium.
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................ [2]

(ii) Another student cools a blue solution containing \([\text{CoCl}_4]^{2-}\). The blue solution turns pink.
What does this information indicate about the forward reaction?
................................................................................................................................................
................................................................................................................................................ [1]

(f) Another compound of cobalt is \(\text{Co(OH)}_3\).
Deduce the charge on the cobalt ion in \(\text{Co(OH)}_3\).
............................................................................................................................................... [1]

Ethanol is a member of the homologous series of alcohols.
(a) Give two characteristics of members of a homologous series.
1 .....................................................................................................................................
2 .....................................................................................................................................

(b) The structure of ethanol is shown.

Complete the dot-and-cross diagram to show the electron arrangement in a molecule of ethanol. Show outer shell electrons only.


(c) Ethanol can be produced by the catalytic addition of steam to ethene or by the fermentation of glucose.
(i) Write a chemical equation for the production of ethanol by the catalytic addition of steam to ethene.
.................................................................................................................. [1]
(ii) Write a chemical equation for the production of ethanol by the fermentation of glucose, $C_6H_{12}O_6$.
.................................................................................................................. [1]
(iii) State one advantage of producing ethanol by the catalytic addition of steam to ethene.
Your answer must not refer to cost.
.................................................................................................................. [1]
(iv) State one advantage of producing ethanol by the fermentation of glucose.
Your answer must not refer to cost.
.................................................................................................................. [1]

(d) Ethanol can be oxidised to ethanoic acid.
State the chemical reagent needed to oxidise ethanol to ethanoic acid.
..................................................................................................................

(e) Ethanoic acid reacts with ethanol in the presence of an acid catalyst. The products are an organic compound and water.
(i) Draw the structure of the organic compound formed. Show all of the atoms and all of the bonds.
[2]
(ii) State the name of the organic compound formed.
.................................................................................................................. [1]
(iii) Which homologous series does the organic compound formed belong to?
.................................................................................................................. [1]

(f) Ethanoic acid, $CH_3COOH$, is a weak acid. It reacts with copper(II) carbonate to form the salt copper(II) ethanoate, $Cu(CH_3COO)_2$.
(i) What is meant by the term weak when applied to acids?
.................................................................................................................. [1]
(ii) Describe how a crystalline sample of copper(II) ethanoate can be prepared starting with ethanoic acid and copper(II) carbonate.
.................................................................................................................. .................................................................................................................. .................................................................................................................. .................................................................................................................. .................................................................................................................. [3]
(iii) Write the word equation for the reaction between ethanoic acid and copper(II) carbonate.
.................................................................................................................. [1]

(a) Nickel(II) iodide crystals are hydrated. A sample of hydrated nickel(II) iodide crystals has the following composition by mass: Ni, 14.01%; I, 60.33%; H, 2.85%; O, 22.81%.

Calculate the empirical formula of the hydrated nickel(II) iodide crystals.

empirical formula = ................................... [2]

(b) Molten nickel(II) iodide can be electrolysed using the apparatus shown.



During electrolysis, charge is transferred through the copper wires and through the molten nickel(II) iodide.

(i) Name the type of particles which transfer charge through the copper wires.
............................................................................................................................... [1]

(ii) Name the type of particles which transfer charge through the molten nickel(II) iodide.
............................................................................................................................... [1]

(iii) Predict the products of the electrolysis of molten nickel(II) iodide. Write an ionic half-equation for the formation of one of these products.
products .............................................................................................................................
ionic half-equation ........................................................................................................... [3]

(c) A student electrolysed copper(II) sulfate solution using the two sets of apparatus shown.



In apparatus $A$ the student used carbon electrodes.
In apparatus $B$ the student used copper electrodes.

The student made the following observations.

[Table_1]

(i) Explain why the mass of the negative electrode increased in both sets of apparatus.
...............................................................................................................................
............................................................................................................................... [1]

(ii) Name the gas that formed the bubbles seen in apparatus A.
............................................................................................................................... [1]

(iii) Explain why the mass of the positive electrode decreased in apparatus B.
...............................................................................................................................
............................................................................................................................... [1]

(iv) Suggest what happens to the colour of the solution in apparatus A and apparatus B as the electrolysis progresses. Explain your answer.
colour of the solution in apparatus A ...........................................................
colour of the solution in apparatus B ...........................................................
explanation ........................................................................................................
...............................................................................................................................
............................................................................................................................... [3]

Calcium chlorate(V), Ca(ClO₃)₂, is made by reacting calcium hydroxide with chlorine gas.
6Ca(OH)₂ + 6Cl₂ → Ca(ClO₃)₂ + 5CaCl₂ + 6H₂O
(a) 8.88 g of calcium hydroxide and 7200 cm³ of chlorine gas are mixed together.
(i) How many moles is 8.88 g of calcium hydroxide?
.................................. mol [1]
(ii) How many moles of chlorine gas is 7200 cm³?
.................................. mol [2]
(iii) What is the maximum number of moles of calcium chlorate(V) that can be made from 8.88 g of calcium hydroxide and 7200 cm³ of chlorine gas?
.................................. mol [1]
(iv) What is the maximum mass of calcium chlorate(V) that can be made from 8.88 g of calcium hydroxide and 7200 cm³ of chlorine gas?
.................................. g [2]
The experiment is repeated using different amounts of calcium hydroxide and chlorine gas. The maximum mass of calcium chlorate(V) that can be made in the experiment is 4.84 g.
(v) The actual mass of calcium chlorate(V) made in the experiment is 3.63 g. Calculate the percentage yield.
percentage yield = .................................. % [1]

(b) Calcium chlorate(V) undergoes thermal decomposition.
The only products are calcium chloride and a colourless gas.
(i) What must be done to calcium chlorate(V) to make it thermally decompose?
........................................................................................... [1]
(ii) Write a chemical equation for the thermal decomposition of calcium chlorate(V).
........................................................................................... [2]

(c) Chloric(V) acid, HClO₃, is a strong acid. It can be made from calcium chlorate(V).
(i) What colour is methyl orange indicator in chloric(V) acid?
........................................................................................... [1]
(ii) Define the term acid in terms of proton transfer.
........................................................................................... [1]
(iii) Complete the chemical equation to show HClO₃ behaving as an acid in water.
HClO₃ + H₂O → ...................... + ...................... [1]