Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2018 Summer Zone 2

The names of nine gases are given.

ammonia
carbon monoxide
chlorine
ethane
ethene
helium
hydrogen
neon
oxygen

(a) Answer the following questions about these gases. Each gas may be used once, more than once or not at all. State which gas:

(i) bleaches damp litmus paper
............................................................................................................ [1]

(ii) dissolves in water to form an alkali
............................................................................................................ [1]

(iii) is a monatomic gas with ten protons in its nucleus
............................................................................................................ [1]

(iv) is formed when hydrocarbons undergo incomplete combustion
............................................................................................................ [1]

(v) is an unsaturated hydrocarbon.
............................................................................................................ [1]

(b) Diatomic hydrogen molecules contain covalent bonds.
State what is meant by the terms:

(i) diatomic
............................................................................................................. [1]
.............................................................................................................

(ii) covalent bonds
............................................................................................................. [1]
.............................................................................................................

(c) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of chlorine. Show outer shell electrons only.
[2]

The table shows the percentage by volume of each of the gases present in the exhaust gases from a petrol engine with a catalytic converter.

[Table_1]

(a) (i) Calculate the percentage by volume of nitrogen in the exhaust gases.
......% [1]
(ii) Which gas shown in the table is present in the lowest percentage by volume?
...................................................................................................................... [1]
(b) (i) Give one adverse effect of oxides of nitrogen on health.
...................................................................................................................... [1]
(ii) Balance the chemical equation for the reaction of nitrogen dioxide with sodium hydroxide.
.....NO₂ + .....NaOH → NaNO₃ + NaNO₂ + H₂O [2]
(iii) State the name of the salt with the formula NaNO₃.
...................................................................................................................... [1]
(c) Petrol contains saturated hydrocarbons.
State what is meant by the terms:
(i) saturated ...................................................................................................................... [1]
(ii) hydrocarbon ...................................................................................................................... [2]
(d) The table shows the composition of a sample of dry natural gas.

[Table_2]

Calculate the percentage by volume of hydrocarbons in the sample of dry natural gas.
......% [1]

(a) The structures of two compounds, A and B, are shown.

(i) How many different types of atoms are present in compound A?
...........................................................................................................................[1]
(ii) On structure B draw a circle around the alcohol functional group. [1]
(iii) Compounds A and B are formed in the body by enzyme-catalysed reactions.
What is the purpose of a catalyst?
...........................................................................................................................[1]
(iv) Enzymes are polymers of compounds called amino acids.
What is meant by the term polymer?
...........................................................................................................................[1]

(b) Ethanoic acid is a carboxylic acid.
(i) Give one property of ethanoic acid.
...........................................................................................................................[1]
(ii) Complete the structure of ethanoic acid showing all of the atoms and all of the bonds.
[1]

(c) Ethanoic acid can be made by the oxidation of ethanol.
(i) The melting point of ethanol is -114°C.
The boiling point of ethanol is 78°C.
What is the physical state of ethanol at -120°C?
Explain your answer.
...........................................................................................................................[2]
(ii) Complete the sentences about the manufacture of ethanol using words from the list.
a catalyst addition an enzyme cracking ethane ethene high low
Ethanol can be manufactured by the .......................................... of steam to .......................................... .
The reaction takes place at a .......................................... temperature in the presence of .......................................... .
[4]

This question is about manganese and its compounds.
(a) Potassium manganate(VII) is soluble in water.
A purple crystal of potassium manganate(VII) was placed in the middle of a piece of damp filter paper.
After 1 hour, the purple colour had spread over most of the filter paper.

[Image of experiment]

Explain these observations using the kinetic particle model.
...............................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
................................................................................................................
[3]

(b) Potassium manganate(VII) is produced from manganese(IV) oxide by an oxidation reaction.
What is meant by the term \textit{oxidation}?
...............................................................................................................
...............................................................................................................
[1]

(c) Potassium manganate(VII) decomposes when heated. The products are oxygen and manganese(IV) oxide.
(i) Describe a test for oxygen.
test .........................................................................................................
result .......................................................................................................
[2]
(ii) Manganese(IV) oxide reacts with concentrated hydrochloric acid.
Balance the chemical equation for this reaction.
$MnO_2 + ...HCl \rightarrow MnCl_2 + Cl_2 + ...H_2O$
[2]

(d) The table compares the reactivity of four metals with hydrochloric acid of the same concentration.

[Table]
| metal | reactivity with hydrochloric acid |
|------------|--------------------------------------------------------------------|
| lead | No bubbles seen. Metal does not disappear. |
| magnesium | Rapid formation of bubbles. Metal disappears rapidly. |
| manganese | Steady formation of bubbles. Metal disappears slowly. |
| tin | Bubbles formed slowly. Metal disappears very slowly. |

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

(e) Manganese is a transition element. Sodium is an element in Group I of the Periodic Table.
Describe three ways in which the properties of manganese differ from those of sodium.
1 ................................................................................................................
2 ................................................................................................................
3 ................................................................................................................
[3]

(a) Electrolysis of concentrated aqueous sodium chloride can be done using the apparatus shown.
(i) During electrolysis, a gas is produced at each electrode.
Complete the diagram to show how the gases can be collected. [1]
(ii) The positive electrode is called the anode.
State the name of the negative electrode. [1]
(iii) Predict the main products of the electrolysis of concentrated aqueous sodium chloride at:
the negative electrode ...................................................................................................................
the positive electrode. .................................................................................................................. [2]
(iv) Give the name of a suitable element to use as the electrodes in this electrolysis. [1]

(b) Sodium hydroxide is manufactured by the electrolysis of sodium chloride.
(i) After electrolysis, 1000 cm^3 of solution contains 750 g of sodium hydroxide.
What mass of sodium hydroxide is present in 200 cm^3 of this solution? [1]
(ii) What effect would impurities have on the melting point of sodium hydroxide? [1]

(c) Describe how you could prepare a sample of solid sodium chloride from a solution of sodium chloride. [1]

This question is about isotopes.

(a) An atom of an isotope of nitrogen is represented by the symbol shown.

$^{15}_{7}\text{N}$

Describe the structure of an atom of this isotope of nitrogen.
In your answer, include:
• the position of the protons, neutrons and electrons in the atom
• the number of protons, neutrons and electrons present in the atom.
..........................................................
.......................................................................
...........................................................
.......................................................................
...........................................................
.......................................................................
......................... [5]

(b) What is meant by the term \text{isotopes}?
..........................................................
.......................................................................
...........................................................
............................... [2]

(c) Give \text{one} industrial use of radioactive isotopes.
..........................................................
....................................................................... [1]

(a) The properties of some Group VII elements are shown in the table.

[Table_1]
The table includes columns for 'element', 'melting point in °C', 'boiling point in °C', 'density at room temperature in g/cm³', and 'colour'.
The rows list data for chlorine, bromine, iodine, and astatine.

(i) Complete the table to suggest:
• the density of iodine
• the melting point of astatine
• the colour of astatine.

(ii) Suggest why the density of chlorine at room temperature is much lower than the density of bromine and astatine at room temperature.

.................................................................................................................................
................................................................................................................................. [1]

(iii) Describe the trend in the boiling points of the halogens.

.................................................................................................................................
................................................................................................................................. [1]

(b) Aqueous bromine reacts with aqueous potassium iodide.

Complete the word equation for this reaction.

bromine + potassium iodide → ................................. + .................................

[2]

(c) A compound has the formula $C_2F_4Cl_2$.

Calculate the relative molecular mass of $C_2F_4Cl_2$.

Show all your working.
Use your Periodic Table to help you.

relative molecular mass = ............................... [2]

(a) Suggest two factors that should be kept constant in this experiment.
1 ................................................................................................................................................
2 ................................................................................................................................................ [2]

(b) The table shows the temperature changes when four different fuels, A, B, C and D, are burned.

[Table_1]
Which fuel gave the greatest temperature rise per gram?
.......................................................................................................................................................... [1]

(c) Ethanol is a fuel.
Give one other use of ethanol.
..................................................................................................................................................... [1]

(d) The energy level diagram for the complete combustion of ethanol is shown.


(i) Complete the diagram by filling in the missing reactant and the missing product.
.............................................................................................................................. [2]
(ii) Is the complete combustion of ethanol exothermic or endothermic? Use the information in the diagram to explain your answer.
.....................................................................................................................................................
..................................................................................................................................................... [1]

(e) A steel can is used in the experiment.
(i) Stainless steel is an alloy of iron. What is meant by the term alloy?
.......................................................................................................................................................
....................................................................................................................................................... [1]
(ii) Describe the arrangement and type of motion of the particles in solid iron.
arrangement .................................................................................................................................
type of motion ............................................................................................................................. [2]
(iii) Suggest why stainless steel is used instead of pure iron for making cutlery.
...................................................................................................................................................... [1]