Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2017 Summer Zone 1

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

Answer the following questions about these atoms.
Each atom may be used once, more than once or not at all.
Which atom, A, B, C, D or E,
(i) has a complete outer shell of electrons, $\text{............................. [1]}$
(ii) has a proton number of 15, $\text{............................. [1]}$
(iii) has 4 shells containing electrons, $\text{............................. [1]}$
(iv) is a fluorine atom, $\text{............................. [1]}$
(v) is an atom of a metallic element? $\text{............................. [1]}$
(b) Complete the table to show the number of electrons, neutrons and protons in the chlorine atom and bromide ion shown.
[Table_1]
$$\begin{array}{|c|c|c|c|} \hline & \text{number of electrons} & \text{number of neutrons} & \text{number of protons} \\ \hline \frac{35}{17}\text{Cl} & 17 & & \\ \hline \frac{79}{35}\text{Br}^- & & 44 & \\ \hline \end{array}$$

(a) The table shows the ions present in a 1000 $cm^3$ sample of polluted river water.

[Table_1]

Ion Present | Formula of Ion | Mass Present in mg/1000 $cm^3$
--------------------------------------------------------
calcium | $Ca^{2+}$ | 2.0
chloride | $Cl^-$ | 1.3
hydrogencarbonate | $HCO_3^-$ | 2.0
magnesium | $Mg^{2+}$ | 1.0
potassium | $K^+$ | 4.0
silicate | $SiO_3^{2-}$ | 12.0
sodium | $Na^+$ | 11.0
| $SO_3^{2-}$ | 3.0

Answer these questions using the information from the table.
(i) Which positive ion is present in the highest concentration?
..................................................................................... [1]
(ii) State the name of the ion $SO_3^{2-}$.
..................................................................................... [1]
(iii) Calculate the mass of silicate ions present in 250 $cm^3$ of this sample.
mass of silicate ions = ......................... mg [1]
(iv) Calculate the mass of solid formed when all the water is evaporated from the 1000 $cm^3$ sample.
mass of solid formed = ......................... mg [1]
(v) Name the compound containing $Ca^{2+}$ ions and $HCO_3^-$ ions.
..................................................................................... [1]

(b) Describe a test for sodium ions.
test ................................................................................
result ............................................................................. [2]

(c) The formulae of some chlorides are given.

aluminium chloride, $AlCl_3$
calcium chloride, $CaCl_2$
sodium chloride, $NaCl$

Deduce the formula for magnesium chloride.
..................................................................................... [1]

(d) Molten calcium chloride can be electrolysed using inert electrodes.
Predict the products of this electrolysis at
the negative electrode (cathode), .................................
the positive electrode (anode). ............................................... [2]

The diagram shows part of the structures of three substances, X, Y and Z, at room temperature and pressure.

(a) Describe substances X, Y and Z in terms of
• their bonding,
• the arrangement of their particles,
• the motion of their particles.
.............................................................................................................................................................................................
.............................................................................................................................................................................................
.............................................................................................................................................................................................
.............................................................................................................................................................................................
.............................................................................................................................................................................................
.............................................................................................................................................................................................
.............................................................................................................................................................................................
............................................................................................................................................................................................. [5]

(b) A closed gas syringe contains substance X.
Describe what happens to the volume of substance X in the syringe when the pressure is increased. The temperature remains constant. Explain your answer in terms of particles.
.............................................................................................................................................................................................
............................................................................................................................................................................................. [2]

(c) Substance Z is diamond. Diamond is used in jewellery.
Give one other use of diamond.
............................................................................................................................................................................................. [1]

(d) Substance Y undergoes physical and chemical changes.
Which two of the following are physical changes? Explain your answer.
A Substance Y dissolves easily in water.
B An aqueous solution of substance Y gives a white precipitate with acidified aqueous silver nitrate.
C Substance Y melts at 801 °C.
D Substance Y reacts with concentrated sulfuric acid.
.............................................................................................................................................................................................
............................................................................................................................................................................................. [3]

Chlorine is an element in Group VII of the Periodic Table.

(a) Chlorine is a diatomic molecule.
Explain what is meant by the term diatomic.
............................................................................................................ [1]

(b) Aqueous chlorine reacts with aqueous potassium bromide.
$$Cl_2 + 2KBr \rightarrow Br_2 + 2KCl$$
(i) How does this equation show that chlorine is more reactive than bromine?
............................................................................................................ [1]

(ii) Aqueous potassium bromide and aqueous potassium chloride are both colourless.
Predict the colour change when aqueous chlorine reacts with aqueous potassium bromide.
............................................................................................................ [1]

(iii) Complete the chemical equation for the reaction of aqueous bromine with aqueous potassium iodide.
$$Br_2 + 2KI \rightarrow \text{................ + ................}$$
............................................................................................................ [2]

(c) Describe a test for iodide ions.
test ..................................................................................................................
.......................................................................................................................
result ................................................................................................................
....................................................................................................................... [2]

(d) Chlorine is used to make the polymer PVC.
(i) Give one other use of chlorine.
....................................................................................................................... [1]

(ii) The monomer used to make PVC is made by the thermal decomposition of dichloroethane.
$$CH_2Cl-CH_2Cl \rightarrow CH_2=CHCl + HCl$$
Explain what is meant by the term thermal decomposition.
...................................................................................................................
................................................................................................................... [2]

(iii) PVC is a non-biodegradable plastic.
Describe two pollution problems caused by non-biodegradable plastics.
1 ...............................................................................................................
2 ............................................................................................................... [2]

Citronellol is found in rose oil. The structure of citronellol is shown.

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

(b) How many hydrogen atoms are there in one molecule of citronellol?
................................................................................................................ [1]

(c) What feature of the citronellol structure shows that it is unsaturated?
................................................................................................................ [1]

(d) The table shows the properties of some alkanes.
[Table_1]

(a) The table shows the properties of some metals.

[Table_1]

Use the information in the table to answer the questions.

(i) Which metal would be most useful for making overhead power cables? Give two reasons for your answer.

metal ................................
reason 1 ........................................................................................................................
reason 2 ........................................................................................................................

[2]

(ii) Why is iron and not tungsten used to reinforce concrete?
..........................................................................................................................

[1]

(iii) The front part of a space rocket is called a nose cone. The nose cone gets very hot as the space rocket moves through the air.

Which metal is best to make a space rocket nose cone? Explain your answer.
..........................................................................................................................

[1]

(b) Tungsten is a transition element.

State two physical properties of transition elements which are not shown by Group I elements.
1 ..........................................................................................................................
2 ..........................................................................................................................

[2]

(c) When extremely hot tungsten reacts with oxygen, tungsten(VI) oxide is formed.

Balance the chemical equation for this reaction.

.......W + .......O₂ → 2WO₃

[2]

(d) Some information about the reaction of four metals with oxygen is given.

cobalt: reacts slowly at high temperatures
iron: thin wire burns when heated strongly
magnesium: burns when heated
tungsten: reacts very slowly at extremely high temperatures

List these metals in order of their reactivity. Put the least reactive metal first.

least reactive .............................................................. most reactive

[2]

(e) The table compares the time taken for reaction of an alloy with ethanoic acid, nitric acid and phosphoric acid, each at three different concentrations. The time taken for the alloy to decrease in mass by 1.0 g was measured. All other conditions were kept the same.

[Table_2]

(i) How does the concentration of acid affect the rate of reaction?
..........................................................................................................................
..........................................................................................................................

[1]

(ii) Which acid reacts most rapidly with the alloy?
..........................................................................................................................

[1]

(iii) Predict how long it would take for the alloy to decrease in mass by 1.0 g using phosphoric acid of concentration 0.03 mol/dm³.

time taken = .............................. hours

[1]

(iv) Suggest which one of these pH values is the pH of concentrated aqueous ethanoic acid. Draw a circle around the correct answer.

pH 4        pH 7        pH 10        pH 13

[1]

Carbon is an element in Group IV of the Periodic Table. It reacts with oxygen to form carbon dioxide.
(a) The energy level diagram for this reaction is shown.

Explain how this diagram shows that the reaction is exothermic.
....................................................................................................................................................................
.................................................................................................................................................................. [1]
(b) Carbon monoxide, carbon dioxide and methane are all atmospheric pollutants.
• Give the sources of these gases.
• Describe the effects that both carbon dioxide and methane have on the environment.
• State an adverse effect of carbon monoxide on health.
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
.................................................................................................................................................................... [5]

(c) Calcium carbonate decomposes to form calcium oxide (lime) and carbon dioxide.
(i) State one use of calcium oxide.
.................................................................................................................................................................... [1]
(ii) Calculate the relative formula mass of calcium carbonate, CaCO$_3$. Show all your working. Use your Periodic Table to help you.
relative formula mass = ................................. [2]
(d) Carbon and magnesium are both insoluble in water. Carbon does not react with hydrochloric acid but magnesium reacts to form a soluble salt and a gas which escapes into the air.
Suggest how you could prepare a pure dry sample of carbon from a mixture of carbon powder and magnesium powder.
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
....................................................................................................................................................................
.................................................................................................................................................................... [3]