Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2017 Winter Zone 1

The table gives information about five particles. The particles are all atoms or ions.

\[ \begin{array}{|c|c|c|c|} \hline \text{particle} & \text{number of protons} & \text{number of neutrons} & \text{number of electrons} \\ \hline \text{A} & 6 & 8 & 6 \\ \text{B} & 12 & 12 & 12 \\ \text{C} & 13 & 14 & 10 \\ \text{D} & 8 & 8 & 10 \\ \text{E} & 11 & 12 & 11 \\ \hline \end{array} \]

Answer the following questions using the information in the table.
Each particle may be used once, more than once or not at all.

(a) Which particle, \( A, B, C, D \) or \( E, \)

(i) is an atom with atomic number 12,
\text{............................................................................................................................} [1]

(ii) is an atom with nucleon number 14,
\text{............................................................................................................................} [1]

(iii) is an ion with a positive charge,
\text{............................................................................................................................} [1]

(iv) has only one electron in its outer shell?
\text{............................................................................................................................} [1]

(b) \( D \) is an ion of an element.
Identify the element and write the formula of \( D \).
\text{............................................................................................................................} [2]

The graph shows how the temperature of a substance changes as it is cooled over a period of 30 minutes. The substance is a gas at the start.

Each letter on the graph may be used once, more than once or not at all.
(a) Which letter, S, T, V, W, X, Y or Z, shows when
(i) the particles in the substance have the most kinetic energy,
.................................................................................................................... [1]
(ii) the particles in the substance are furthest apart,
.................................................................................................................... [1]
(iii) the substance exists as both a gas and a liquid?
.................................................................................................................... [1]
(b) Use the graph to estimate the freezing point of the substance.
............................. °C [1]
(c) Name the change of state directly from a solid to a gas.
.................................................................................................................... [1]
(d) When smoke is viewed through a microscope, the smoke particles in the air appear to jump around.
(i) What term describes this movement of the smoke particles?
.................................................................................................................... [1]
(ii) Explain why the smoke particles move in this way.
....................................................................................................................
....................................................................................................................
.................................................................................................................... [2]

(a) When magnesium is added to aqueous copper(II) sulfate a reaction occurs. The ionic equation for the reaction is shown.

Mg + Cu^{2+} \rightarrow Mg^{2+} + Cu

(i) Give one change you would observe during this reaction.

................................................................................................................ [1]

(ii) Explain why this is a redox reaction.

................................................................................................................
................................................................................................................ [1]

(iii) Identify the oxidising agent in this reaction. Give a reason for your answer.

................................................................................................................
................................................................................................................ [2]

(iv) A redox reaction occurs when magnesium is heated with iron(III) oxide. Write a chemical equation for the reaction between magnesium and iron(III) oxide.

................................................................................................................ [2]

(b) The metal iron and the alloy steel are commonly used materials. A problem with them is that they rust.

(i) How does painting iron and steel prevent rusting?

................................................................................................................
................................................................................................................ [1]

(ii) Magnesium blocks can be attached to the bottom of steel boats. Explain how the magnesium blocks prevent the whole of the bottom of the boat from rusting.

................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................ [2]

(iii) Replacing the magnesium blocks with copper blocks does not prevent rusting. Explain why the copper blocks do not prevent rusting.

................................................................................................................
................................................................................................................ [1]

(a) Ethanol, $C_2H_5OH$, can be made by fermentation.
(i) Complete the chemical equation for the formation of ethanol by fermentation.
$C_6H_{12}O_6 \rightarrow ...... C_2H_5OH + .............................$
[2]

(a) Ethanol, $C_2H_5OH$, can be made by fermentation.
(ii) State two conditions required for fermentation.
1 ..............................................................................................................................
2 ..............................................................................................................................
[2]

(b) Ethanol can also be made by the catalytic hydration of ethene. The equation for the reaction is shown.
$C_2H_4 + H_2O \rightarrow C_2H_5OH$
(i) Name a suitable catalyst for this reaction.
..............................................................................................................................
[1]
(ii) Calculate the maximum mass of ethanol that can be made from 56 g of ethene.
maximum mass of ethanol = ............................. g
[2]

(c) Ethanol can be oxidised to form ethanoic acid.
(i) Name a suitable oxidising agent for this reaction.
..............................................................................................................................
[1]
(ii) A molecule of ethanoic acid has the structure shown.

Complete the dot-and-cross diagram to show the electron arrangement in ethanoic acid. Show outer shell electrons only.

[3]

(d) Ethanoic acid is a weak acid.
(i) When referring to an acid, what is meant by the term weak?
..............................................................................................................................
[1]
(ii) Describe how you could show that ethanoic acid is a weaker acid than hydrochloric acid.
..............................................................................................................................
..............................................................................................................................
..............................................................................................................................
[3]

(e) Carboxylic acids react with alcohols to make esters.
The structure of an ester is shown.

Draw the structures of the carboxylic acid and alcohol from which this ester can be made. Give the names of the carboxylic acid and alcohol.
structure of the carboxylic acid
name of the carboxylic acid ..............................................................................................................................
structure of the alcohol
name of the alcohol ..............................................................................................................................
[4]

(a) Solid copper(II) carbonate undergoes thermal decomposition. One of the products of the thermal decomposition is copper(II) oxide.
(i) State the colour change of the solid seen during the reaction.
start colour ..........................................................................................................................
end colour ............................................................................................................................. [1]
(ii) Write a chemical equation for the thermal decomposition of copper(II) carbonate.
............................................................................................................................................. [1]

(b) Copper(II) carbonate reacts with dilute nitric acid. One of the products of the reaction is a solution of copper(II) nitrate.
(i) Describe tests for copper(II) ions and nitrate ions. Include the results of the tests.
copper(II) ions .............................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
nitrate ions .................................................................................................................................
..............................................................................................................................................
.............................................................................................................................................. [4]
(ii) Copper(II) nitrate undergoes thermal decomposition.
Balance the chemical equation for the thermal decomposition of copper(II) nitrate.
......Cu(NO$_3$)$_2$ → ......CuO + ......NO$_2$ + ......O$_2$ [1]

(c) Nitrogen dioxide, NO$_2$, exists in equilibrium with dinitrogen tetroxide, N$_2$O$_4$.
Nitrogen dioxide is brown and dinitrogen tetroxide is colourless.
$$\text{2NO}_2(g) \rightleftharpoons \text{N}_2\text{O}_4(g)$$
brown colourless
(i) A sample of nitrogen dioxide and dinitrogen tetroxide at equilibrium was placed in a closed gas syringe.
The syringe plunger was pushed in. This increased the pressure in the gas syringe. The temperature was kept constant.

nitrogen dioxide and dinitrogen tetroxide at equilibrium

gas syringe
end blocked

State how the colour of the gas in the syringe changed. Explain your answer in terms of the position of the equilibrium.
..............................................................................................................................................
..............................................................................................................................................
..............................................................................................................................................
.............................................................................................................................................. [3]
(ii) A sealed tube containing nitrogen dioxide and dinitrogen tetroxide at equilibrium was cooled in an ice bath at constant pressure. The contents of the tube became paler.
Suggest an explanation for this observation in terms of the position of the equilibrium.
..............................................................................................................................................
..............................................................................................................................................
.............................................................................................................................................. [2]

Aluminium is extracted from aluminium oxide by electrolysis.

(a) Why is aluminium not extracted by heating aluminium oxide with carbon?
................................................................................................................................................
................................................................................................................................................ [1]

(b) Aluminium oxide is an ionic compound with a high melting point.

(i) Complete the dot-and-cross diagram to show the electron arrangement in one of the oxide ions present in aluminium oxide. Include the charge on the oxide ion. One of the aluminium ions is shown.

[2]

(ii) The melting point of aluminium oxide is above 2000°C.
Explain why aluminium oxide has a high melting point.
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................ [2]

(c) Aluminium can be extracted by electrolysis using the apparatus shown.

(i) Name the type of particle responsible for the transfer of charge in
the wires, ................................................................................................................................
the electrolyte. ....................................................................................................................... [2]

(ii) Give two reasons why cryolite is used.
1 ........................................................................................................................................
2 ........................................................................................................................................ [2]

(iii) Write the ionic half-equation for the formation of aluminium during the electrolysis.
................................................................................................................................................
[1]

(iv) Explain how carbon dioxide gas is formed at the anodes.
................................................................................................................................................
................................................................................................................................................
................................................................................................................................................
[3]

(d) When a piece of aluminium is placed in dilute hydrochloric acid, there is no immediate visible reaction.
If the aluminium is left in the dilute hydrochloric acid for several hours, bubbles start to form.
Explain why aluminium does not react immediately with dilute hydrochloric acid.
................................................................................................................................................
[1]

Copper(II) oxide reacts with dilute hydrochloric acid.
$$\text{CuO(s) + 2HCl(aq) } \rightarrow \text{ CuCl}_2\text{(aq) } + \text{ H}_2\text{O(l)}$$
6.00 g of copper(II) oxide were added to 50.0 cm$^3$ of 1.00 mol/dm$^3$ hydrochloric acid. This was an excess of copper(II) oxide.

(a) The rate of the reaction can be increased by increasing the concentration of the hydrochloric acid or by heating it.

(i) In terms of collisions, explain why increasing the concentration of the hydrochloric acid increases the rate of the reaction.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................. [2]

(ii) In terms of collisions, explain why heating the hydrochloric acid increases the rate of the reaction.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................. [2]

(b) (i) Calculate the number of moles of copper(II) oxide added to the hydrochloric acid.
moles of copper(II) oxide = ............................ mol [2]

(ii) Calculate the number of moles of hydrochloric acid used.
moles of hydrochloric acid = ............................ mol [1]

(iii) Calculate the mass of copper(II) oxide that did not react.
mass of copper(II) oxide that did not react = ............................ g [2]

(c) Crystals of hydrated copper(II) chloride were obtained from the solution at the end of the reaction.
The crystals had the following composition by mass: Cl, 41.52%; Cu, 37.43%; H, 2.34%; O, 18.71%.
Calculate the empirical formula of the crystals.
empirical formula = ............................ [2]