Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2021 Summer Zone 3

Give the name of the process that is used:
(a) to produce large molecules from monomers ............................................................................................................................. [1]
(b) to separate oxygen from liquid air ............................................................................................................................. [1]
(c) to make ethanol from glucose ............................................................................................................................. [1]
(d) to separate water from aqueous sodium chloride ............................................................................................................................. [1]
(e) to produce aluminium from aluminium oxide in molten cryolite ............................................................................................................................. [1]
(f) to separate the products of hydrolysis of long chain carbohydrates ............................................................................................................................. [1]
(g) to separate an aqueous solution from an undissolved solid. ............................................................................................................................. [1]
[Total: 7]

Complete the table to:
\begin{itemize}
\item deduce the number of protons, electrons and neutrons in the boron atom and chloride ion shown
\item identify the atom or ion represented by the final row.
\end{itemize}

\[\begin{array}{|c|c|c|c|}\hline \text{formula} & \text{number of protons} & \text{number of electrons} & \text{number of neutrons} \\ \hline ^{11}_{5}\text{B} & & 5 & \\ \hline ^{35}_{17}\text{Cl}^- & 17 & & \\ \hline & 24 & 21 & 30 \\ \hline \end{array}\]

Sodium reacts with fluorine to form sodium fluoride, NaF.

(a) Write a chemical equation for this reaction.
............................................................................................................................................................................ [2]

(b) Sodium fluoride is an ionic compound.
Complete the diagram to show the electron arrangement in the outer shells of the ions present in sodium fluoride.
Give the charges on both ions.



[3]

(c) Aqueous sodium fluoride undergoes electrolysis.
(i) State what is meant by the term electrolysis.
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.................................................................................................................................................................................. [2]
(ii) Name the products formed at the positive electrode (anode) and the negative electrode (cathode) when dilute aqueous sodium fluoride undergoes electrolysis.

anode .......................................................................................................................................................................
cathode ..................................................................................................................................................................... [2]

(d) Molten sodium fluoride undergoes electrolysis.
(i) Name the products formed at the positive electrode (anode) and the negative electrode (cathode) when molten sodium fluoride undergoes electrolysis.

anode .......................................................................................................................................................................
cathode ..................................................................................................................................................................... [2]
(ii) Write the ionic half-equation for the reaction at the negative electrode (cathode).
............................................................................................................................................................................ [1]

(e) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of fluorine, $\text{F}_2$.
Show the outer electrons only.



[1]

(f) The melting points and boiling points of fluorine and sodium fluoride are shown.

[Table_1]

(i) Deduce the physical state of fluorine at $-195\degree\text{C}$. Use the data in the table to explain your answer.

physical state .........................................................................................................................................................
explanation .............................................................................................................................................................
.................................................................................................................................................................................. [2]

(ii) Explain, in terms of structure and bonding, why sodium fluoride has a much higher melting point than fluorine.
Your answer should refer to the:
• types of particle held together by the forces of attraction
• types of forces of attraction between particles
• relative strength of the forces of attraction.
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.............................................................................................................................................................................. [3]

[Total: 18]

Hydrogen iodide, HI, decomposes into iodine and hydrogen. The reaction is reversible. $$2HI(g) \rightleftharpoons I_{2}(g) + H_{2}(g)$$ colourless gas purple gas colourless gas
A gas syringe containing a mixture of hydrogen iodide, iodine and hydrogen gases was sealed. After reaching equilibrium the mixture was a pale purple colour.

(a) State what is meant by the term equilibrium.
........................................................
........................................................
........................................................ [2]
(b) The plunger of the gas syringe is pushed in. The position of equilibrium does not change. The colour of the gaseous mixture turns darker purple.
The temperature remains constant.
$$2HI(g) \rightleftharpoons I_{2}(g) + H_{2}(g)$$ colourless gas purple gas colourless gas
(i) Explain why the position of equilibrium does not change.
..................................................................................... [1]
(ii) Suggest why the colour of the gaseous mixture turns darker purple even though the position of equilibrium does not change.
..................................................................................... [1]
(c) The forward reaction is endothermic.
(i) State what happens to the position of equilibrium when the temperature is decreased.
........................................................ [1]
(ii) State what happens to the rate of the forward reaction and the rate of the backward reaction when the temperature of the mixture is decreased.
rate of the forward reaction ........................................................
rate of the backward reaction ........................................................ [2]

This question is about salts.
(a) Salts that are soluble in water can be made by the reaction between insoluble carbonates and dilute acids. Zinc sulfate is soluble in water.
You are provided with solid zinc carbonate, ZnCO₃, and dilute sulfuric acid, H₂SO₄.
Describe how you would make a pure sample of zinc sulfate crystals.
Your answer should include:
• practical details
• how you would make sure that all the dilute sulfuric acid has reacted
• a chemical equation for the reaction.
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(b) Some sulfates decompose when heated.
When hydrated iron(II) sulfate is heated strongly, sulfur dioxide gas is given off.
(i) Describe a test for sulfur dioxide.
test .........................................................................................................................................
observations .........................................................................................................................................
(ii) Complete the equation for the decomposition of hydrated iron(II) sulfate.
.....FeSO₄·7H₂O → Fe₂O₃ + SO₂ + SO₃ + .....H₂O

(c) Some chlorides are hydrated.
When hydrated barium chloride crystals, BaCl₂·xH₂O, are heated they give off water.
BaCl₂·xH₂O(s) → BaCl₂(s) + xH₂O(g)
A student carries out an experiment to determine the value of x in BaCl₂·xH₂O.
step 1 Hydrated barium chloride crystals are weighed.
step 2 The hydrated barium chloride crystals are then heated.
step 3 The remaining solid is weighed.
(i) Describe how the student can be sure that all the water is given off.
................................................................................................................................................
................................................................................................................................................
........................................................................................................................ [2]
(ii) In an experiment, 4.88 g of BaCl₂·xH₂O is heated until all the water is given off. The mass of BaCl₂ remaining is 4.16 g.
[M_r: BaCl₂, 208; H₂O, 18]
Determine the value of x using the following steps.
• Calculate the number of moles of BaCl₂ remaining. ....... mol
• Calculate the mass of H₂O given off. ....... g
• Calculate the number of moles of H₂O given off. ....... mol
• Determine the value of x. x = .......

This question is about metals.
(a) Iron is extracted from its main ore in a blast furnace.

(i) Coke and iron ore are added at the top of the blast furnace.
Name one other substance that is added at the top of the blast furnace. ............................................................................................................................................... [1]
(ii) Name the substance that leaves the blast furnace at A.
............................................................................................................................................... [1]
(iii) Iron ore is mainly iron(III) oxide, $\text{Fe}_2\text{O}_3$.
Name a substance that reduces iron(III) oxide to iron in the blast furnace. ............................................................................................................................................... [1]
(iv) Temperatures inside a blast furnace can reach 2000°C.
Name two substances that react together, in the blast furnace, to produce this high temperature. ............................................................................................................................................... [1]
(v) Name two waste gases that leave the blast furnace.
1 ...............................................................................................................................................
2 ............................................................................................................................................... [2]

(b) Zinc is extracted from zinc blende.
(i) Name the main zinc compound that is present in zinc blende. ............................................................................................................................................... [1]
(ii) When zinc is extracted, it is formed as a gas.
The gaseous zinc is then converted into molten zinc.
State the name of this physical change. ............................................................................................................................................... [1]
(c) Name the alloy that contains zinc and copper only. ............................................................................................................................................... [1]
(d) Copper has the following properties.
• It has a high melting point.
• It has a high density.
• It is a good conductor of electricity.
• It has variable oxidation states.
• It forms a basic oxide.
• It forms soluble salts.
(i) Give two properties from the list in which copper differs from Group I elements.
1 ...............................................................................................................................................
2 ............................................................................................................................................... [2]
(ii) Give two properties from the list in which copper is similar to Group I elements.
1 ...............................................................................................................................................
2 ............................................................................................................................................... [2]
[Total: 13]

Many organic compounds contain carbon, hydrogen and oxygen only.

(a) An organic compound R has the following composition by mass.
C, 69.77%; H, 11.63%; O, 18.60%
Calculate the empirical formula of compound R.
empirical formula = ............................ [2]

(b) Compound S has the empirical formula $CH_2O$ and a relative molecular mass of 60.
Calculate the molecular formula of compound S.
molecular formula = ............................ [2]

(c) Compounds T and V have the same molecular formula, $C_3H_6O_2$.

• Compound T is an ester.
• Compound V contains a $-COOH$ functional group.

(i) State the name given to compounds with the same molecular formula but different structures.
.............................................................................................................. [1]

(ii) Name the homologous series that V is a member of.
.............................................................................................................. [1]

(iii) Draw a structure of compound T. Show all of the atoms and all of the bonds.
Name compound T.
name ....................................................................................................... [3]

(iv) Draw the structure of compound V. Show all of the atoms and all of the bonds.
Name compound V.
name ....................................................................................................... [2]

(d) Ethanol can be produced from long chain alkanes such as decane, $C_{10}H_{22}$, in a two-step process.

For each of the two steps:
• name the type of chemical reaction that occurs
• write a chemical equation.

step 1: decane to ethene
type of reaction ...................................................................................
chemical equation .............................................................................

step 2: ethene to ethanol
type of reaction ...................................................................................
chemical equation ............................................................................. [4]