Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2021 Summer Zone 1

(a) The electronic structures of five atoms, A, B, C, D and E, are shown.

Answer the following questions about these electronic structures. Each electronic structure may be used once, more than once or not at all.
State which electronic structure, A, B, C, D or E, represents:
(i) an atom in Group II of the Periodic Table
................................................................................................................. [1]
(ii) an atom with a proton number of 13
................................................................................................................. [1]
(iii) an atom that forms a stable ion with a single negative charge
................................................................................................................. [1]
(iv) an atom of a non-metal that forms a giant covalent structure
................................................................................................................. [1]
(v) an atom of a metal used in food containers.
................................................................................................................. [1]
(b) Complete the table to show the number of electrons, neutrons and protons in the vanadium atom and calcium ion shown.

[Table_1]
$$\begin{array}{ccc}\text{number of electrons} & \text{number of neutrons} & \text{number of protons}\\ \hline \text{}^{51}_{23}\text{V} & 23 & ext{.......................} & ext{.......................} \\ \text{}^{48}_{20}\text{Ca}^{2+} & 28 & ext{.......................} & ext{.......................}\end{array}$$
[3]
[Total: 8]

The table shows the masses of some of the ions in 1000 cm³ of fruit juice.

[Table_1]
(a) Answer these questions using only the information in the table.
(i) State which negative ion has the highest mass in 1000 cm³ of fruit juice.
......................................................................................................................... [1]
(ii) Give the formulae of the ions in ammonium sulfate.
............................................. and ............................................................. [1]
(iii) Calculate the mass of sodium ions in 200 cm³ of fruit juice.
mass = ........................... mg [1]

(b) Describe a test for lithium ions.
test ......................................................................................................................
observations ......................................................................................................... [2]

(c) Ions of the element potassium, K, are present in most fertilisers.
State the names of two other elements that are in most fertilisers.
1 .............................................................................................................................
2 ............................................................................................................................. [2]

(d) Orange juice is acidic.
Draw a circle around the pH of orange juice.
pH 4 pH 7 pH 10 pH 13 [1]

(e) Some soils are acidic.
Give the names of two compounds that are used to make soils less acidic.
1 .............................................................................................................................
2 ............................................................................................................................. [2]

(f) Hydrogen chloride is an acidic gas produced when concentrated hydrochloric acid evaporates.
(i) Describe the arrangement and separation of the molecules in hydrogen chloride gas.
arrangement .................................................................................................
..........................................................................................................................
separation .................................................................................................
.......................................................................................................................... [2]

(ii) A long glass tube is set up as shown.

At first, the blue litmus paper does not turn red.
After a short time, the litmus paper turns red.
Explain these observations using the kinetic particle model.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
.......................................................................................................................... [3]

The table shows some properties of four Group I elements.

[Table_1]

(a) (i) Complete the table by predicting:
• the boiling point of rubidium
• the atomic radius of potassium. [2]

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

(iii) Deduce the physical state of potassium at 60°C. Explain your answer.
......................................................................................................................................................
......................................................................................................................................................
...................................................................................................................................................... [2]

(b) Caesium is a radioactive element with a proton number of 55.

(i) Define proton number.
...................................................................................................................................................... [1]

(ii) State one industrial use of radioactive isotopes.
...................................................................................................................................................... [1]

(c) Sodium hydride, NaH, reacts with iron(III) oxide.

(i) Balance the equation for this reaction.
$$ ext{Fe}_2 ext{O}_3 + 3 ext{NaH} ightarrow ..... ext{Fe} + ..... ext{NaOH}$$ [2]

(ii) Explain how this equation shows that iron(III) oxide is reduced.
...................................................................................................................................................... [1]

The structure of malic acid is shown.

(a) (i) On the structure draw a circle around the alcohol functional group. [1]

(ii) Deduce the formula of malic acid to show the number of carbon, hydrogen and oxygen atoms.  [1]

(b) When malic acid is heated it forms compound F.

The structure of compound F is shown.

Explain why compound F is described as unsaturated.    [1]

(c) Compound F can form polymers.

(i) State the meaning of the term polymer.    [2]

(ii) State the name of the polymer formed when ethene is polymerised.    [1]

(d) Ethanoic acid is a carboxylic acid.

Describe the observations made when dilute ethanoic acid reacts with:   [2]

• magnesium
• litmus solution

(e) The graph shows how the pH changes when dilute ethanoic acid is added slowly to aqueous sodium hydroxide.

(i) Deduce the pH of the aqueous sodium hydroxide before the addition of dilute ethanoic acid.  [1]

(ii) Deduce the volume of dilute ethanoic acid added when the pH is neutral.    [1]

(a) Calcium oxide is made by the thermal decomposition of calcium carbonate.
(i) State the meaning of the term thermal decomposition.
...............................................................................................................................
............................................................................................................................... [2]
(ii) Describe a test for calcium ions.
test .......................................................................................................................
observations ..................................................................................................... [2]

(b) Carbon dioxide is produced when dilute hydrochloric acid reacts with calcium carbonate.

$$\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$$
(i) Complete the diagram to show how to measure the volume of carbon dioxide produced during this reaction.

[2]
(ii) Describe the effect of each of the following on the rate of reaction of dilute hydrochloric acid with calcium carbonate.
• The concentration of hydrochloric acid is decreased.
All other conditions stay the same.
...............................................................................................................................
• The temperature is increased.
All other conditions stay the same.
............................................................................................................................... [2]

(c) Carbon dioxide is also formed when the hydrocarbon $\text{C}_3\text{H}_8$ is completely combusted.
(i) State the meaning of the term hydrocarbon.
...............................................................................................................................
............................................................................................................................... [2]
(ii) The hydrocarbon $\text{C}_3\text{H}_8$ is called propane.
Name the homologous series that propane belongs to.
............................................................................................................................... [1]
(iii) Name two substances formed by the incomplete combustion of propane.
............................................................ and ........................................................
[2]

[Total: 13]

This question is about water.
(a) The water in rivers often contains pollutants such as acids. Describe how universal indicator paper can be used to determine the pH value of the water. ......................................................................................................................................................
......................................................................................................................................................
...................................................................................................................................................... [2]
(b) The diagram shows some of the stages in water treatment.

(i) Air is blown through the aeration tank. Name the two gases that make up most of the air. .................................................... and ........................................................... [2]
(ii) After aeration, the water still contains large insoluble particles. The filter is made up of fine sand and stones. Explain how the filter helps purify the water.
.........................................................................................................................................................
.........................................................................................................................................................
......................................................................................................................................................... [2]
(iii) Explain why chlorine is used in water treatment.
......................................................................................................................................................... [1]
(c) Anhydrous cobalt(II) chloride is used to test for water. State the colour change in this test. from ......................................................... to ............................................................... [2]

(a) Molten lead(II) bromide is electrolysed using carbon electrodes.

(i) State the products of this electrolysis at:

the negative electrode ..........................................................................................................
the positive electrode. .......................................................................................................... [2]

(ii) State the name of another substance which can be used as an inert electrode.
............................................................................................................................................. [1]

(b) When aqueous magnesium chloride is electrolysed using carbon electrodes, hydrogen gas is produced at the negative electrode.

Complete the dot-and-cross diagram to show the electron arrangement in one molecule of hydrogen.

[1]
[Total: 4]

(a) The table shows some properties of five elements, P, Q, R, S and T.

[Table_1]

Use only the elements shown in the table to answer this question.

State which two of the elements, P, Q, R, S and T, are covalent molecules.
Give two reasons for your answer.

elements .................................................. and ..................................................
reason 1 .............................................................................................................
reason 2 .............................................................................................................

(b) Element T is on the left-hand side of the Periodic Table.
Suggest whether its oxide is acidic or basic.
Give a reason for your answer.
..............................................................................................................
..............................................................................................................

(c) Krypton is an element in Group VIII of the Periodic Table.
Explain, using ideas about electronic structure, why krypton is unreactive.
..............................................................................................................
..........................................................................................................

(d) Sodium is an element in Group I of the Periodic Table. Iron is a transition element.
Iron has a higher melting point and higher boiling point than sodium.
Give two other ways in which the properties of transition elements differ from the properties of Group I elements.
1 ............................................................................................................
2 ............................................................................................................

(e) The table compares the reactivity of four metals with dilute hydrochloric acid.

[Table_2]

Put the four metals in order of their reactivity.
Put the least reactive metal first.
least reactive _________________________ most reactive
______________________ ______________________ ______________________ ______________________

(f) Hot iron reacts with steam. The reaction is reversible.
Complete the equation by writing the symbol for a reversible reaction in the box.

3Fe + 4H₂O □ Fe₃O₄ + 4H₂

(g) Steel is an alloy of iron.
State the meaning of the term alloy.
..........................................................................................................