Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2022 Winter Zone 2

(a) State the number of covalent bonds each carbon atom has in diamond.

(b) State the term used to describe the structure of diamond.

(c) Name an oxide that has a similar structure to diamond.

(d) Describe the arrangement of atoms in graphite.

(e) Explain how graphite conducts electricity.

(f) Buckminsterfullerene is a simple molecular form of carbon. The relative molecular mass of Buckminsterfullerene is 720. Determine the number of carbon atoms in one molecule of Buckminsterfullerene.

(g) All forms of carbon burn to produce carbon dioxide. Name the substance used to test for carbon dioxide.

Sodium is a reactive metal.

(a) Suggest why sodium is stored under oil.
............................................................................................................................ [1]

(b) Sodium burns in air to form sodium oxide, Na₂O.

(i) State the term given to a reaction in which a substance burns.
............................................................................................................................ [1]

(ii) State the colour of the flame seen when sodium burns.
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(iii) Write a chemical equation for the reaction which takes place when sodium burns in air to form sodium oxide.
............................................................................................................................ [2]

(iv) Complete the dot-and-cross diagram to show the electron arrangement and charges of the ions in sodium oxide.

[3]

(c) Sodium reacts vigorously with water to form aqueous sodium hydroxide, NaOH, which is a strong base.

(i) Explain in terms of proton transfer what is meant by a base.
............................................................................................................................ [1]

(ii) State a pH number that indicates the presence of a strong alkali.
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(iii) State the colour of methyl orange in aqueous sodium hydroxide.
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(iv) The equation for the reaction is shown.
2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g)
Calculate the concentration of NaOH(aq) formed, in g/dm³, when 0.345 g of sodium is added to 50.0 cm³ of distilled water. Assume there is no change in volume.
Use the following steps.
● Calculate the number of moles of Na added.
= ................................. mol
● Determine the number of moles of NaOH formed.
= ................................. mol
● Calculate the concentration of NaOH in mol/dm³.
concentration of NaOH = ................................. mol/dm³
● Determine the M_r of NaOH and calculate the concentration of NaOH in g/dm³.
concentration of NaOH = ................................. g/dm³ [5]

(d) When NaOH(aq) is added to aqueous iron(III) chloride, FeCl₃(aq), a solid product is formed.

(i) Name the type of reaction where a solid is formed from two solutions.
............................................................................................................................ [1]

(ii) State the colour of this solid product.
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(iii) Name this solid product.
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(iv) Write the ionic equation for the reaction. Include state symbols.
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Sulfuric acid is manufactured by an industrial process. Sulfur is obtained from sulfur-containing metal ores. The sulfur in the metal ore is converted to sulfur dioxide which is then oxidised to sulfur trioxide as shown.

$$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$$

(a) Name a metal ore which contains sulfur.
........................................................................................................................... [1]

(b) Describe the process which converts metal ores to sulfur dioxide.
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(c) Name the industrial process used to manufacture sulfuric acid.
........................................................................................................................... [1]

(d) The reaction that produces sulfur trioxide is an equilibrium. The forward reaction is exothermic.

(i) State the temperature and pressure used to make sulfur trioxide.
temperature = ............................ °C
pressure = ............................ atm [2]

(ii) Name the catalyst used.
........................................................................................................................... [1]

(iii) Describe two features of an equilibrium.
1 ...........................................................................................................................
2 ........................................................................................................................... [2]

(iv) State the effect, if any, on the position of equilibrium when the following changes are made.
Explain your answers.
temperature is increased ........................................................................................... ...........................................................................................................................
pressure is increased ........................................................................................... ........................................................................................................................... [4]

(v) Explain, in terms of particles, what happens to the rate of reaction when the temperature is increased.
........................................................................................................................... ........................................................................................................................... ........................................................................................................................... ........................................................................................................................... [3]

(e) Name the compound formed when sulfuric acid reacts with ammonia.
........................................................................................................................... [1]

A student prepares magnesium sulfate crystals, $\text{MgSO}_4$, by adding excess magnesium to dilute sulfuric acid.

(a) Write the chemical equation for this reaction.   [1]

(b) Describe two observations which show the reaction has finished.   [2]

(c) The excess magnesium is removed by filtration.

State the general name given to a solid separated from a solution by filtration.   [1]

(d) The aqueous magnesium sulfate is heated until crystals begin to appear.

(i) Suggest the name for a solution in which no more solute can dissolve.  [1]

(ii) Suggest why more crystals of magnesium sulfate appear on cooling. [1]

(e) Magnesium sulfate crystals have the formula, $\text{MgSO}_4\cdot x\text{H}_2\text{O}$, where $x$ is a whole number of molecules of water.

The student heats the crystals to remove the molecules of water.

 $\text{MgSO}_4\cdot x\text{H}_2\text{O}(s) \rightarrow \text{MgSO}_4(s) + x\text{H}_2\text{O}(g)$

(i) Name the term given to crystals containing molecules of water. [1]

(ii) The student heats a sample of $\text{MgSO}_4\cdot x\text{H}_2\text{O}$ and finds it has lost 0.140 moles of $\text{H}_2\text{O}$ and has 2.40 g of $\text{MgSO}_4$ remaining.

Determine the value of $x$. Use the following steps.   [3]

Calculate the $M_r$ of $\text{MgSO}_4$.

Determine the number of moles of $\text{MgSO}_4$ formed.

Determine the value of $x$ in $\text{MgSO}_4\cdot x\text{H}_2\text{O}$.

(f) If the student uses dilute nitric acid instead of dilute sulfuric acid, the salt formed is magnesium nitrate, $\text{Mg(NO}_3)_2$.

Write the chemical equation for the reaction when solid magnesium nitrate is heated.   [2]

Ethane is an alkane which undergoes a photochemical reaction with chlorine as shown.
$C_2H_6(g) + Cl_2(g) \rightarrow C_2H_5Cl(l) + HCl(g)$

(a) Write the general formula of alkanes.
............................................................................................................................................................................ [1]

(b) State why this reaction is described as a photochemical reaction.
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(c) In this reaction, an atom of hydrogen is replaced with a chlorine atom.
State the name of this type of organic reaction.
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(d) In this reaction, one of the products is chloroethane.
Name the other product.
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(e) The energy profile diagram of this reaction is shown.

(i) Name the energy change labelled A.
............................................................................................................................................................................ [1]
(ii) Name the energy change labelled B.
............................................................................................................................................................................ [1]
(iii) State how the energy profile diagram shows this is an exothermic reaction.
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(f) The equation for the reaction can be represented as shown.

Some bond energies are given.
[Table_1]

Use the bond energies in the table to calculate the energy change in this reaction.
Use the following steps.

• Calculate the energy needed to break bonds.
energy = .............................. kJ
• Calculate the energy released in making bonds.
energy = .............................. kJ
• Determine the energy change in this reaction.
energy change in this reaction = .............................. kJ/mol [3]

A carboxylic acid Y has the structure shown.

(a) State the general formula of carboxylic acids. .....................................................................................................................................................................

(b) Name carboxylic acid Y. .....................................................................................................................................................................

(c) Write the molecular formula of carboxylic acid Y. .....................................................................................................................................................................

(d) Complete the dot-and-cross diagram to show the arrangement of electrons in a molecule of carboxylic acid Y.


(e) Carboxylic acid Y will react with propan-1-ol, $C_3H_7OH$, to form ester Z and one other product.
(i) Name and draw the structure of ester Z.
Show all of the atoms and all of the bonds.
name ...............................................................
structure

(ii) Name the other product formed when carboxylic acid Y reacts with propan-1-ol. ........................................................................................................................................
(iii) Name:
• an ester which is a structural isomer of ester Z
........................................................................................................................................
• a carboxylic acid which is a structural isomer of ester Z.
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