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

The names of seven gases are given.

ammonia
ethene
helium
hydrogen
hydrogen chloride
methane
nitrogen

(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) forms an acidic solution in water
....................................................................................................................... [1]

(ii) is monatomic
....................................................................................................................... [1]

(iii) forms 78\% of clean dry air
....................................................................................................................... [1]

(iv) is the main constituent of natural gas
....................................................................................................................... [1]

(v) has molecules which each contain 14 protons.
....................................................................................................................... [1]

(b) (i) Give the names of two elements in the list.
................................................... and .................................................. [1]

(ii) What is meant by the term element?
....................................................................................................................... [1]

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

(a) The table shows the percentage by volume of each of the gases present in the exhaust gases from a petrol engine and a diesel engine.
[Table_1]
(i) In the diesel engine, nitrogen, carbon dioxide and water vapour account for 90.00% of the exhaust gases by volume.
Calculate the percentage by volume of carbon dioxide in the exhaust gases from the diesel engine.
.................................% [1]
(ii) Describe three ways in which the composition of the exhaust gases from the petrol engine differ from the composition of the exhaust gases from the diesel engine.
1 ............................................................................................................
2 ............................................................................................................
3 ............................................................................................................
[3]
(iii) Give one adverse effect of sulfur dioxide on health.
...................................................................................................................[1]

(b) Complete the sentences about the separation of petroleum into fractions using words from the list.

boiling crystallisation density distillation kerosene poly(ethene)

Fractional ............................... of petroleum produces fractions such as gasoline, diesel oil and ............................... . Within each fraction, the molecules have a particular range of ............................... points.
[3]

(c) Balance the chemical equation for the complete combustion of propane.

$C_3H_8 + 5O_2 \rightarrow .....CO_2 + .....H_2O$
[2]

(a) A coloured crystal of cobalt(II) chloride was placed at the bottom of a beaker containing water. After 2 days, the colour had spread throughout the water.



Explain these observations using the kinetic particle model.

(b) Cobalt(II) chloride can be used to test for the presence of water.

$\text{CoCl}_2 \; + \; 6\text{H}_2\text{O} \rightleftharpoons \text{CoCl}_2\cdot6\text{H}_2\text{O}$
anhydrous hydrated
cobalt(II) chloride cobalt(II) chloride

(i) What is meant by the symbol $\rightleftharpoons$?

(ii) Describe how the colour of anhydrous cobalt(II) chloride changes when water is added to it.
from ........................................................... to ...........................................................

(c) A compound of cobalt can be represented by the structure shown.



Deduce the molecular formula of this compound showing the number of cobalt, carbon and oxygen atoms.

(d) The table compares the reactivity of cobalt with that of three other metals.

$\begin{array}{|c|c|c|} \hline \text{metal} & \text{reactivity with cold water} & \text{reactivity with steam} \\ \hline \text{barium} & \text{reacts rapidly} & \text{} \\ \text{cobalt} & \text{no reaction} & \text{reacts slowly when heated} \\ \text{magnesium} & \text{reacts very slowly} & \text{reacts rapidly} \\ \text{zinc} & \text{no reaction} & \text{reacts easily when heated} \\ \hline \end{array}$

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

(e) Cobalt is a transition element. Lithium is an element in Group I of the Periodic Table.

Describe three ways in which the properties of cobalt differ from those of lithium.
1 ...........................................................
2 ...........................................................
3 ...........................................................

(f) When cobalt(II) oxide, CoO, is heated in air, an oxide with the formula Co$_3$O$_4$ is formed.

Balance the chemical equation for this reaction.
.....CoO + O$_2$ $\rightarrow$ 2Co$_3$O$_4$

(g) When Co$_3$O$_4$ is heated with hydrogen, cobalt metal can be formed.

Co$_3$O$_4$ + 4H$_2$ $\rightarrow$ 3Co + 4H$_2$O

How does this equation show that Co$_3$O$_4$ is reduced?

(a) The structure of compound P is shown.

(i) What feature of the structure of compound P shows that it is unsaturated?
................................................................................................................................. [1]
(ii) Describe how the colour of aqueous bromine changes when an excess of compound P is added to it.
from ............................................... to ............................................ [2]
(iii) The melting point of compound P is $-129^{\circ}$C.
The boiling point of compound P is $97^{\circ}$C.
What is the physical state of compound P at $-120^{\circ}$C? Explain your answer.
.................................................................................................................................
................................................................................................................................. [2]
(b) Ethanol is an alcohol with two carbon atoms.
(i) Draw the structure of ethanol showing all of the atoms and all of the bonds. [1]
(ii) Ethanol can be manufactured by fermentation.
Complete the sentences about fermentation using words from the list.
30$^{\circ}$C, 300$^{\circ}$C, distillation, electrolysis
elements, enzymes, salt, sugar
A flask containing .............................. solution and yeast is heated to ............................. .
The yeast contains ............................ which catalyse the reaction. The ethanol is separated by ....................... . [4]
(iii) Ethanol can be used as a fuel.
Give one other use of ethanol in industry.
................................................................................................................................. [1]
(iv) The energy level diagram for the complete combustion of ethanol is shown.

Explain how this diagram shows that the reaction is exothermic.
.................................................................................................................................
................................................................................................................................. [1]
(v) Carbon dioxide and water can be formed when ethanol burns in a limited supply of air.
State the name of two other products which can be formed when ethanol burns in a limited supply of air.
................................................. and ............................................... [2]

(a) Molten lead(II) bromide can be electrolysed using the apparatus shown.

The negative electrode is called the cathode. State the name of the positive electrode.
................................................................. [1]
(b) Predict the products of the electrolysis of molten lead(II) bromide at:
the negative electrode ................................................
the positive electrode ................................................. [2]
(c) Lead(II) bromide is insoluble in cold water. Sodium bromide is soluble in cold water.
Describe how you could obtain crystals of sodium bromide from a mixture of solid lead(II) bromide and solid sodium bromide.
................................................................ [3]
(d) When chlorine is bubbled through a colourless aqueous solution of sodium bromide, the solution turns orange-brown.
Name the orange-brown substance. Suggest, using ideas about reactivity of the halogens, why the reaction occurs.
orange-brown substance .........................................
why the reaction occurs ........................................... [2]
(e) What is the colour of the precipitate formed when aqueous silver nitrate is added to aqueous sodium bromide?
...................................................................... [1]
(f) Complete the sentence about the formation of a chloride ion from a chlorine atom.
A chloride ion is formed when a chlorine atom gains one .................. . [1]

This question is about isotopes.
(a) An atom of an isotope of oxygen is represented by the symbol shown.
$$^{17}_{8}O$$
Describe the structure of an atom of this isotope of oxygen.
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) Which \textbf{two} statements about isotopes are correct?
Tick \textbf{two} boxes.
Isotopes of the same element have different numbers of protons. [ ]
Isotopes of the same element have different numbers of neutrons. [ ]
Isotopes are always radioactive. [ ]
The isotope $^{235}_{92}U$ is a source of energy. [ ]
$^{14}_{6}C$ and $^{14}_{7}N$ are isotopes of each other. [ ]
[2]
(c) What is meant by the term \textit{nucleon number}?
.............................................................................................................................................................................
............................................................................................................................................................................. [1]

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

[Table_1]

(i) Complete the table to estimate:
● the relative hardness of potassium
● the melting point of rubidium.
[2]

(ii) Use the information in the table to predict what you would observe when lithium reacts with cold water.
...................................................................................................................................................[1]

(b) Write the electronic structure of a sodium atom.
.....................................................................................................................................................[1]

(c) When sodium reacts with water, an alkaline solution is formed.

$$2Na + 2H_2O \rightarrow 2NaOH + H_2$$

(i) Use the information in the equation to explain why the solution formed is alkaline.
.....................................................................................................................................................[1]

(ii) Describe how you could use a named indicator solution to show that the solution is alkaline.
.....................................................................................................................................................
.....................................................................................................................................................[2]

(d) Sodium tetrahydridoborate, NaBH₄, is an ionic compound.

Calculate the relative formula mass of NaBH₄.
Show all your working.
Use your Periodic Table to help you.

relative formula mass = .................................... [2]

The apparatus shown is used to investigate the rate of reaction between calcium carbonate and hydrochloric acid at 30°C.
(a) Name the piece of apparatus labelled A in the diagram.
....................................................................................................................... [1]
(b) Describe how this apparatus can be used to find the rate of reaction.
.......................................................................................................................
.......................................................................................................................
....................................................................................................................... [2]
(c) The experiment is repeated at 20°C. All other conditions are kept the same.
How does the decrease in temperature affect the rate of reaction?
....................................................................................................................... [1]
(d) The experiment is repeated using the same mass of different size pieces of calcium carbonate. All other conditions are kept the same.
The sizes of the pieces of calcium carbonate are:
● large pieces
● small pieces
● powder
Complete the table by writing the sizes of the pieces in the first column.
[Table_1]
| size of the pieces of calcium carbonate | initial rate of reaction in cm³ gas/s |
|-------------------------------|-----------------------------------|
| | 5 |
| | 2 |
| | 12 |
[1]
(e) Give the names of the three products formed when calcium carbonate reacts with hydrochloric acid.
1 ........................................................................................
2 ........................................................................................
3 ........................................................................................ [2]