Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2019 Winter Zone 3

This question is about solids and gases.

(a) The list gives the names of eight substances which are gases at room temperature.

ammonia
butane
carbon dioxide
carbon monoxide
chlorine
methane
propene
sulfur dioxide

Answer the following questions about these gases.
Each gas may be used once, more than once or not at all.

State which gas:

(i) is a poisonous product formed by the incomplete combustion of carbon
....................................................................................................... [1]

(ii) is an alkene
....................................................................................................... [1]

(iii) is formed when limestone is thermally decomposed
....................................................................................................... [1]

(iv) is an element
....................................................................................................... [1]

(v) causes acid rain.
....................................................................................................... [1]

(b) When a piece of solid carbon dioxide is placed in a warm room, it undergoes sublimation.

(i) What is meant by the term *sublimation*?
....................................................................................................... [2]

(ii) Use the kinetic particle model to describe the motion and separation of the particles in:
solid carbon dioxide ...........................................................................
.......................................................................................................
carbon dioxide gas.
.......................................................................................................
....................................................................................................... [4]

Biogas is made by fermenting animal and vegetable waste.
(a) The table shows the percentage composition of the gases present in a sample of biogas.

[Table_1]

(i) Deduce the percentage of water vapour present in this sample of biogas.
................................................................................................................................. [1]
(ii) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of water. Show outer shell electrons only.



[2]
(iii) Describe a chemical test for water.
test ..........................................................................................................................
observation .......................................................................................................... [2]

(b) (i) Balance the chemical equation for the oxidation of methane to form hydrogen.
.....CH_4 + O_2 \rightarrow 2CO + .....H_2 [2]
(ii) Which one of these compounds belongs to the same homologous series as methane?
Draw a circle around the correct answer.
butane butene methanoic acid methanol [1]

(c) Methane is present in the refinery gas fraction produced by the fractional distillation of petroleum.
(i) Match the fractions on the left with their uses on the right. The first one has been done for you.

[Table_2]

[2]
(ii) Describe the fractional distillation of petroleum.
In your answer:
• state the physical property on which the separation of the fractions depends
• describe how the distillation is done to separate the fractions.
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................................................................................................................................. [3]

(d) The biogas fermentation mixture contains a small amount of compound M.
The structure of compound M is shown.



(i) On the structure shown, draw a circle around the carboxylic acid functional group. [1]
(ii) How many different types of atoms are present in compound M?
................................................................................................................................. [1]

A student investigated the reaction of magnesium carbonate with an excess of dilute hydrochloric acid.
$$ \text{MgCO}_3 + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{CO}_2 + \text{H}_2\text{O} $$
The rate of reaction can be found by measuring the decrease in the mass of the reaction mixture over time.
The results are shown on the graph.

(a) Determine the mass of the reaction mixture after 58 seconds.
................................................................................................................................. [1]
(b) At which point on the graph, A, B, C or D, was the rate of reaction the fastest? Use the graph to explain your answer.
.................................................................................................................................
................................................................................................................................. [2]
(c) When 0.42 g of magnesium carbonate is used, 120 cm³ of carbon dioxide is formed.
Determine the volume of carbon dioxide produced when 1.26 g of magnesium carbonate reacts completely.
volume of carbon dioxide = ............................... cm³ [1]
(d) What effect do the following have on the rate of this reaction?
• Decreasing the concentration of the acid.
All other conditions are kept the same.
.................................................................................................................................
• Using smaller pieces of magnesium carbonate.
All other conditions are kept the same.
................................................................................................................................. [2]

(a) Deduce the number of protons, electrons and neutrons in this isotope of sulfur.

number of protons ........................................................
number of electrons ......................................................
number of neutrons ......................................................
[3]

(b) Draw the electronic structure of a sulfur atom.
[2]

(c) The table shows some observations made when four metals are heated with liquid sulfur.

[Table_1]

Use this information to put the four metals in order of their reactivity. Put the least reactive metal first.
least reactive ___________________________________ most reactive
[2]

(d) Name one source of sulfur.
................................................................................
[1]

(e) Sulfur is used in the manufacture of sulfur dioxide and sulfuric acid.

(i) Give one different use of sulfur dioxide.
..........................................................................................
[1]

(ii) Complete the word equation for the reaction of dilute sulfuric acid with magnesium.

sulfuric acid + magnesium → ________________ + ________________
[2]

This question is about Group I elements.
(a) The properties of some Group I elements are shown in the table.

[Table_1]

element | melting point in °C | boiling point in °C | relative thermal conductivity | atomic radius / pm
lithium | ...................... | 1342 | 84 | 152
sodium | 97 | 883 | 142 | 186
potassium | 63 | 760 | 102 | ......................
rubidium | 39 | 686 | 58 | 248

(i) Complete the table to estimate:
• the melting point of lithium
• the atomic radius of potassium.
[2]

(ii) Describe the trend in the boiling points of the Group I elements down the group.
.....................................................................................................
[1]

(iii) Caesium is below rubidium in Group I.
Use the information in the table to suggest why it is difficult to predict the thermal conductivity of caesium.
........................................................................................
........................................................................................
[1]

(iv) Predict the physical state of rubidium at 45°C.
Give a reason for your answer.
.....................................................................................................
[2]

(b) Lithium reacts with oxygen to form lithium oxide.
(i) Balance the chemical equation for this reaction.
.....Li + O₂ → .....Li₂O
[2]

(ii) Is lithium oxide an acidic oxide or a basic oxide?
Give a reason for your answer.
..............................................................................................
..............................................................................................
[1]

(iii) State the name of the particle which is lost from a lithium atom when it forms a lithium ion.
..............................................................................................
[1]

(iv) A compound of lithium has the formula C₂H₅Li.
Complete the table to calculate the relative molecular mass of C₂H₅Li.
Use your Periodic Table to help you.

[Table_2]

type of atom | number of atoms | relative atomic mass
carbon | .............. | .............. | ..............
hydrogen | 5 | 1 | 5 × 1 = 5
lithium | .............. | .............. | ..............
relative molecular mass = ..............................
[2]

(a) The chemical equation shows a reaction that produces sodium hydroxide.
$$\text{Na}_2\text{CO}_3 + \text{Ca(OH)}_2 \rightarrow 2\text{NaOH} + \text{CaCO}_3$$
Complete the word equation for this reaction.

[Image_1: Boxes for the word equation]
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(b) Aqueous sodium hydroxide can be used to test for chromium(III) ions and iron(II) ions.
Complete the table to show the expected observations.

[Table_1: Table with columns for ion, and two types of observations]


(c) A student set up a long glass tube as shown.
[Image_2: Diagram of a glass tube with cotton wool and litmus paper]
At first, the litmus paper remained red.
After a short time the litmus paper was completely blue.
Explain these observations using the kinetic particle model.
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(d) Oxides of nitrogen are formed when ammonia is heated with oxygen in the presence of a catalyst.
(i) Suggest why a catalyst is used.
..........................................................................................................................................................
[1]

(ii) State one other process which puts oxides of nitrogen into the atmosphere.
..........................................................................................................................................................
[1]

(iii) State one adverse effect of oxides of nitrogen on health.
..........................................................................................................................................................
[1]


(e) Ammonium nitrate is present in many fertilisers.
Which one of these compounds is also present in many fertilisers?
Tick one box.

barium hydroxide []
potassium phosphate []
sodium chloride []
tin(II) sulfate []


(f) When ammonium chloride dissolves in water, the temperature of the solution decreases.
What is the name for a reaction where the temperature of the solution decreases?
..........................................................................................................................................................

Aluminium is manufactured by the electrolysis of molten aluminium oxide.
(a) Predict the products of the electrolysis of molten aluminium oxide at:
the positive electrode ...............................................................
the negative electrode ..........................................................
[2]
(b) Complete these sentences about the uses of aluminium using words from the list.

conductivity corrosion density heavy malleability reduction strong weak

Aluminium is used in the manufacture of aircraft because it is relatively ................................. and has a low ................................. . Aluminium is used for food containers because of its resistance to ................................. .
[3]
(c) The following statements are about the procedure for making crystals of hydrated aluminium sulfate from aluminium hydroxide and sulfuric acid.

A Filter off the excess aluminium hydroxide.
B Filter off the crystals and dry between filter papers.
C Warm the filtrate to the point of crystallisation.
D Add aluminium hydroxide to warm dilute sulfuric acid and stir.
E Leave the mixture at room temperature to form more crystals.
F Add more aluminium hydroxide to the sulfuric acid until the aluminium hydroxide is in excess.

Put the statements A, B, C, D, E and F in the correct order. The first one has been done for you.

D [2]

This question is about dyes.

(a) Chromatography can be used to separate a mixture of dyes.
S, T, U and W are four different mixtures of dyes.
S, T, U and W were placed on a piece of chromatography paper.
Two pure dyes, X and Y, were also placed on the same piece of chromatography paper.

The results of the chromatography are shown.



(i) Which mixture, S, T, U or W, contains dye X but not dye Y?
.............................................................................................................................. [1]

(ii) Which mixture, S, T, U or W, contains the smallest number of dyes?
.............................................................................................................................. [1]

(iii) Which mixture, S, T, U or W, contains neither dye X nor dye Y?
.............................................................................................................................. [1]

(b) Indigo is a blue dye.

When an alkaline solution of indigo undergoes reduction, it turns colourless.

(i) What is meant by the term reduction?
.............................................................................................................................. [1]

(ii) A piece of white cloth is soaked in the colourless solution.
When the cloth is left in the air it turns blue.

What type of chemical reaction occurs?
Draw a circle around the correct answer.

decomposition fermentation oxidation polymerisation [1]