Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2018 Summer Zone 1

The names of eight gases are given.

ammonia
argon
carbon dioxide
helium
hydrogen
methane
neon
sulfur dioxide

(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) turns damp red litmus paper blue
........................................................................................... [1]

(ii) contributes to the formation of acid rain
........................................................................................... [1]

(iii) is a hydrocarbon which contributes to climate change
........................................................................................... [1]

(iv) is a product of the reaction of copper(II) carbonate with hydrochloric acid
........................................................................................... [1]

(v) is a monatomic gas which has atoms with the electronic structure 2,8,8.
........................................................................................... [1]

(b) (i) Explain why helium and not hydrogen is used to fill party balloons.
........................................................................................... [1]

(ii) Give one use of argon.
........................................................................................... [1]

(c) Carbon dioxide is a compound.

What is meant by the term compound?
........................................................................................... [1]

(d) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of ammonia. 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.

[Table_1]

(a) (i) Calculate the percentage by volume of carbon dioxide in the exhaust gases.

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

(ii) Which gas shown in the table is present in the lowest percentage by volume?

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

(iii) Which \text{two} elements in the table combine to form nitrogen dioxide?

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

(iv) Give the formula for nitrogen dioxide.

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

(v) Where does the nitrogen in the exhaust gases come from?

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

(b) The carbon monoxide in the exhaust gases comes from the incomplete combustion of hydrocarbons.

(i) What is meant by the term \text{hydrocarbon}?

...............................................................................................................................
............................................................................................................................... [2]

(ii) Give \text{one} adverse effect of carbon monoxide on health.

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

(iii) Balance the chemical equation for the complete combustion of pentane.

$C_5H_{12} + 8O_2 \rightarrow .... CO_2 + .... H_2O$ [2]

Limonene is a volatile liquid which smells of oranges.

(a) A teacher placed a beaker of limonene at the front of a classroom.
      At first, the students at the back of the classroom could not smell the limonene.
      After two minutes, the smell of limonene had spread throughout the classroom.
      The air in the classroom was still and calm.

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

      (ii) The melting point of limonene is $-74\degree C$.
            The boiling point of limonene is $176\degree C$.

            What is the physical state of limonene at $-80\degree C$?
            Explain your answer.
      .........................................................................................................................................................................
      ......................................................................................................................................................................... [2]

(b) An enzyme present in peppermint plants is a catalyst for the oxidation of limonene.

      State what is meant by the terms:

      (i) catalyst
      .........................................................................................................................................................................
      ............................................................................................................... [1]

      (ii) oxidation
      .........................................................................................................................................................................
      ............................................................................................................... [1]

(c) Limonene can be made from a colourless compound called $\alpha$-terpineol.
      The structure of $\alpha$-terpineol is shown.



      (i) What feature of the structure of the $\alpha$-terpineol molecule shows that it is an unsaturated compound?
      ..................................................................................................................... [1]

      (ii) Describe how the colour of aqueous bromine changes when an excess of $\alpha$-terpineol is added to it.
      from ................................................................. to ................................................................ [2]

(a) The table shows how easy it is to reduce four metal oxides by heating with carbon.

\[ \begin{array}{|c|c|} \hline \text{metal oxide} & \text{ease of reduction with carbon} \\ \hline \text{chromium(III) oxide} & \text{only reduced above 1700°C} \\ \text{iron(III) oxide} & \text{only reduced above 650°C} \\ \text{magnesium oxide} & \text{not reduced at 1750°C} \\ \text{nickel(II) oxide} & \text{only reduced above 300°C} \\ \hline \end{array} \]

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

(b) Iron is a transition element. Potassium is an element in Group I of the Periodic Table.
Describe three ways in which the properties of iron differ from those of potassium.
1 ................................................................................................................................
2 ................................................................................................................................
3 .................................................................................................................................

(c) Iron wire burns in oxygen.
Balance the chemical equation for this reaction.
...Fe + ...O_2 → Fe_3O_4

(d) Pure iron can be made by reducing iron(III) oxide, \( \text{Fe}_2\text{O}_3 \), with hydrogen.

\( \text{Fe}_2\text{O}_3 + 3\text{H}_2 \rightarrow 2\text{Fe} + 3\text{H}_2\text{O} \)
How does this equation show that iron(III) oxide is reduced?
.................................................................................................................................

(e) When iron reacts with dilute hydrochloric acid, iron(II) chloride is formed.
(i) Describe a test for iron(II) ions.
test .............................................................................................................................
result ..........................................................................................................................
(ii) Another chloride of iron has the structure shown.
[Image of structure here]
Deduce the molecular formula of this compound showing the number of iron and chlorine atoms.
...........................................................................................................................

(f) Some iron nails were placed in bottles under different conditions.
[Image of bottles here]
In which bottles will the iron nails not rust? Give reasons for your answer.
...........................................................................................................................

(a) Complete the sentence about electrolysis using words from the list.

breakdown compound electricity electroplating
element gaseous heat molten

Electrolysis is the ........................... of an ionic ........................... when
........................... or in aqueous solution by the passage of ............................ . [4]

(b) Molten zinc iodide can be electrolysed using the apparatus shown.



On the diagram, label:
• the anode
• the cathode
• the electrolyte [2]

(c) Why are the electrodes made of graphite?

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

(d) Predict the products of the electrolysis of molten zinc iodide at:

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

(e) When chlorine is bubbled through a colourless aqueous solution of zinc iodide, the solution turns brown.

Name the brown substance. Suggest, using ideas about reactivity of the halogens, why this reaction occurs.

............................................................................................................................... [2]

This question is about isotopes.
(a) An atom of an isotope of fluorine is represented by the symbol shown.
$$^{19}_{9}\text{F}$$
Describe the structure of an atom of this isotope of fluorine.
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.
............................................................................................................................................................
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(b) Complete the sentence about isotopes using words from the list.
atomic compound element ions molecular nucleons
Isotopes are atoms of the same ............................. which have the same ............................. number but different numbers of ............................. . [3]

(c) Give one medical use of radioactive isotopes.
............................................................................................................................................ [1]

(d) Which one of the following isotopes is used as a source of energy?
Draw a circle around the correct answer.
$$^{127}_{53}\text{I} \hspace{10pt} ^{235}_{92}\text{U} \hspace{10pt} ^{131}_{54}\text{Xe} \hspace{10pt} ^{66}_{30}\text{Zn}$$ [1]

This question is about Group I elements and their compounds.

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

• A sodium atom gains an electron.
• A sodium atom loses an electron.
• A sodium atom loses a proton.
• A sodium atom gains a proton.

When zinc reacts with hydrochloric acid, hydrogen gas is produced. The graph shows how the volume of hydrogen gas produced changes with time when an excess of zinc is reacted with 0.2 mol/dm³ hydrochloric acid.



(a) Explain why the volume of hydrogen gas remains constant after six minutes.
............................................................................................................................................................................... [1]

(b) What volume of hydrogen gas was released in the first two minutes of the reaction?
............................................................................................................................................................................... [1]

(c) The experiment is repeated using the same volume of 0.1 mol/dm³ hydrochloric acid. All other conditions are kept the same.
On the grid, draw the graph for the experiment using 0.1 mol/dm³ hydrochloric acid. [2]

(d) Give the name of the salt formed when zinc reacts with hydrochloric acid.
............................................................................................................................................................................... [1]

(e) Which one of the following pH values could be the pH of dilute hydrochloric acid? Draw a circle around the correct answer.
pH 1 pH 7 pH 9 pH 13 [1]