Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2022 Winter Zone 3

Atoms and ions are made from small particles called electrons, neutrons and protons.
(a) Complete the table.

[Table_1]
| particle | relative charge | relative mass |
|----------|-----------------|---------------|
| electron | -1 | 1/1840 |
| neutron | | |
| proton | | |

[2]
(b) Information about atoms and ions, A, B and C, is shown in the table.
Complete the table.

[Table_2]
| atom or ion | number of electrons | number of neutrons | number of protons | symbol |
|-------------|---------------------|-------------------|-------------------|-----------------|
| A | 18 | | 20 | \( {}^{42}_{20}\text{Ca}^{2+} \) |
| B | | 18 | | \( {}^{35}_{17}\text{Cl} \) |
| C | 18 | 16 | 16 | |

[6]

The table shows the melting points, boiling points and electrical conductivities of six substances, D, E, F, G, H and I.

The table contains the following data:

(a) Identify the substance, D, E, F, G, H or I, which is:

(i) a liquid at 25°C   [1]

(ii) a gas at 25°C    [1]

(iii) a solid consisting of simple molecules at 25°C.   [1]

(b) Identify the substance, D, E, F, G, H or I, which is a metal. Give a reason for your choice.   [2]

(c) Identify the substance, D, E, F, G, H or I, which has a macromolecular structure. Give two reasons for your choice.   [3]

(d) Identify the substance, D, E, F, G, H or I, which is an ionic solid. Give a reason for your choice.   [2]

Aluminium is extracted from its ore by electrolysis.

(a) Name the ore of aluminium which consists mainly of aluminium oxide.

(b) State what is meant by the term electrolysis.

(c) Electrolysis is carried out on aluminium oxide dissolved in molten cryolite.



(i) Give two reasons why the electrolysis is carried out on aluminium oxide dissolved in molten cryolite instead of electrolysing molten aluminium oxide only.

(ii) Write the ionic half-equation for the reaction occurring at the negative electrode.


(iii) The positive electrodes are made of carbon.

Explain why the positive carbon electrodes are replaced regularly.

(d) Aluminium is more reactive than copper.

When aluminium is added to aqueous copper(II) sulfate, no immediate reaction is seen.

Explain why.

(e) Aluminium reacts with oxygen to form an amphoteric oxide.

(i) State what is meant by the term \textit{amphoteric}.


(ii) The reaction between aluminium oxide and aqueous sodium hydroxide forms a salt containing the negative ion $\text{AlO}_2^-$. The only other product is water.

Write a chemical equation for the reaction between aluminium oxide and aqueous sodium hydroxide.

(f) Gallium is in the same group as aluminium and forms similar compounds.

Predict the formulae of:
gallium(III) chloride          
gallium(III) sulfate.        

This question is about compounds of phosphorus.
(a) Gaseous phosphorus(V) chloride decomposes into gaseous phosphorus(III) chloride and gaseous chlorine.
When the three gases are present in a closed container the system reaches equilibrium.
$\text{PCl}_5(\text{g}) \rightleftharpoons \text{PCl}_3(\text{g}) + \text{Cl}_2(\text{g})$
(i) Complete the table using only the words increases, decreases or no change.
$$\begin{array}{|c|c|c|} \hline & \text{effect on the rate of} & \text{effect on the equilibrium} \\ & \text{the forward reaction} & \text{yield (PCl}_3(\text{g}) \text{ and Cl}_2(\text{g})) \\ \hline \text{increasing the temperature} & & \text{increases} \\ \hline \text{decreasing the pressure} & & \\ \hline \text{adding a catalyst} & & \text{no change} \\ \hline \end{array}$$ [4]
(ii) The table shows that when the temperature increases, the equilibrium yields of $\text{PCl}_3(\text{g})$ and $\text{Cl}_2(\text{g})$ increase.
State what conclusion can be made from this.
................................................................................................................................ [1]
(b) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of phosphorus(III) chloride, $\text{PCl}_3$. Show outer shell electrons only. [2]


(c) Phosphorus oxychloride has the formula $\text{POCl}_3$.
Phosphorus oxychloride is the only product of the reaction between phosphorus(V) chloride, $\text{PCl}_5$, and phosphorus(V) oxide, $\text{P}_4\text{O}_{10}$.
Write a chemical equation for the reaction between phosphorus(V) chloride and phosphorus(V) oxide.
....................................................................................................................................................................................... [2]

(d) Compound $\text{X}$ has the following composition by mass.
$\text{H, 3.66\%}; \text{P, 37.80\%}; \text{O, 58.54\%}$
Calculate the empirical formula of compound $\text{X}$.
empirical formula = .............................. [2]

(e) Compound $\text{Y}$ has the empirical formula $\text{H}_3\text{PO}_4$ and a relative molecular mass of 98.
Deduce the molecular formula of compound $\text{Y}$.
molecular formula = .......................... [1]

(a) Sulfuric acid is manufactured by the Contact process.

stage 1 Molten sulfur burns in air to produce sulfur dioxide.
stage 2 Sulfur dioxide reacts with oxygen to form sulfur trioxide, $SO_3$.
stage 3 Sulfur trioxide reacts with concentrated sulfuric acid to form oleum, $H_2S_2O_7$.
stage 4 Oleum is converted into sulfuric acid.

(i) The equation for the reaction in stage 2 is shown.
$$2SO_2 + O_2 \rightleftharpoons 2SO_3$$
State the temperature and pressure used in stage 2.
Name the catalyst used in stage 2.
temperature ............................................................. °C
pressure ............................................................. atm
catalyst ............................................................. [3]

(ii) Write the chemical equation for the reaction in stage 3.
................................................................................................................ [1]

(iii) Name the substance that reacts with oleum in stage 4.
................................................................................................................ [1]

(b) Name the black solid that is produced when concentrated sulfuric acid is added to sugar, $C_{12}H_{22}O_{11}$.
................................................................................................................ [1]

(c) Dilute sulfuric acid and aqueous potassium hydroxide are used to make aqueous potassium sulfate.
$$H_2SO_4 + 2KOH \rightarrow K_2SO_4 + 2H_2O$$
The method includes use of the following apparatus.

(i) Calculate the volume of $0.0625\, mol/dm^3$ dilute sulfuric acid, $H_2SO_4$, that completely reacts with $25.0\, cm^3$ of $0.100\, mol/dm^3$ potassium hydroxide, $KOH$, to produce aqueous potassium sulfate.
Use the following steps.
• Calculate the number of moles of KOH in $25.0\, cm^3$ of $0.100\, mol/dm^3$ KOH.
= ............................ mol
• Deduce the number of moles of $H_2SO_4$ that react with KOH.
= ............................ mol
• Calculate the volume of $H_2SO_4$ required.
volume = ............................ $cm^3$ [3]

(ii) The experiment is repeated using the same volume and concentration of potassium hydroxide and the same concentration of dilute sulfuric acid. In this second experiment, the product is aqueous potassium hydrogensulfate, $KHSO_4$.

$H_2SO_4 + KOH \rightarrow KHSO_4 + H_2O$

Use your answer to (c)(i) and the equation to deduce the volume of $H_2SO_4$ required.
volume = ............................ $cm^3$ [1]

(d) Aqueous potassium hydrogensulfate, $KHSO_4$(aq), contains the ions $K^+$(aq), $H^+$(aq) and $SO_4^{2-}$(aq).
Describe the observations in the following tests.

(i) A flame test is carried out on aqueous potassium hydrogensulfate.
................................................................................................................ [1]

(ii) Solid copper(II) carbonate is added to aqueous potassium hydrogensulfate.
................................................................................................................
................................................................................................................ [2]

(iii) An acidic solution containing aqueous barium ions, $Ba^{2+}$(aq), is added to aqueous potassium hydrogensulfate.
................................................................................................................ [1]

(e) Write the ionic equation for the reaction in (d)(iii).
Include state symbols.
................................................................................................................ [3]

(a) Chloroethene $(\text{CH}_2=\text{CHCl})$ can be manufactured from 1,2-dichloroethane $(\text{CH}_2\text{ClCH}_2\text{Cl})$.

The equation can be represented as shown.



(i) Some bond energies are given.

[Table_1]

Use the bond energies in the table to calculate the energy change, in kJ/mol, of the reaction.

Use the following steps.

● Calculate the energy needed to break bonds.

energy = ............................. kJ

● Calculate the energy released when bonds form.

energy = ............................. kJ

● Calculate the energy change of the reaction.

energy change of the reaction = ............................. kJ/mol

(ii) Deduce whether the energy change for this reaction is exothermic or endothermic.
Give a reason for your answer.
...............................................................................................................................................................
...............................................................................................................................................................

(b) Part of a synthetic polymer is shown.



(i) State the number of monomer units that are needed to make the part of the polymer shown.
.........................................................................................................................................................

(ii) Name and draw the structure of the monomer used to make this polymer. Show all of the atoms and all of the bonds.

name ...............................................
structure

(iii) State the empirical formula of the polymer.
..........................................................................................................................................................

(c) Proteins are natural polymers.

Proteins are broken down into amino acids. The process is similar to how complex carbohydrates are broken down to give simple sugars.

(i) Name the type of reaction in which proteins are broken down into amino acids.
...............................................................................................................................................................

(ii) Name two types of substance that are used to break down proteins into amino acids.
1 .........................................................................................................................................................
2 .........................................................................................................................................................

(iii) Amino acids are colourless.

A sample containing a mixture of amino acids is separated. Each amino acid is detected and identified.

● Name the process used to separate the amino acids.

...............................................................................................................................................................

● Name the type of substance used to detect the amino acids.

...............................................................................................................................................................

● Give the symbol of the value used to determine the identity of each amino acid after separation and detection.

...............................................................................................................................................................

(d) Proteins are natural polymers. Proteins contain amide linkages.

Synthetic polyamides also contain amide linkages.

(i) Name a synthetic polyamide.
...............................................................................................................................................................

(ii) Identify the two functional groups present in the monomers used to produce synthetic polyamides.
1 .........................................................................................................................................................
2 .........................................................................................................................................................