Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2015 Summer Zone 2

The structures of six compounds containing oxygen are shown below.

(a) Answer the following questions about these compounds. Each compound, A, B, C, D, E or F, may be used once, more than once or not at all.
(i) Which compound is a compound of a noble gas? ...........[1]
(ii) Which compound can be used as a fertiliser? ..............[1]
(iii) Which compound can be used to neutralise acidic soil? ..............[1]
(iv) Which compound is a greenhouse gas? ..............[1]
(v) Which two compounds are ionic? .............. and .............[1]
(vi) Which two compounds react to form calcium sulfate? ............. and .............[1]
(b) Complete the symbol equation for the reaction of compound A with hydrochloric acid.
$$ ext{CaO + ......HCl} ightarrow ext{CaCl}_2 + ext{...........}$$ [2]
(c) Complete the following sentence about compounds using words from the list below.
atoms
combined
mixtures
molecules
separated
unreactive
A compound is a substance containing two or more different ..................................... which are chemically ................................... .
[2]

An aqueous solution of sodium hydrogen carbonate is added to an aqueous solution of citric acid. The mixture is stirred. The temperature is measured before and after the addition.



(a) Explain how this experiment shows that the reaction is endothermic.
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(b) Citric acid reacts with sodium hydroxide to form the soluble salt sodium citrate. Describe how you could prepare pure dry crystals of sodium citrate from citric acid and sodium hydroxide.
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(c) Citric acid can be made by fermentation. Ethanol can also be made by fermentation. Which of the following are required to make ethanol by fermentation?
Tick two boxes.

- enzymes from yeast
- temperature above 100 °C
- high pressure
- concentrated sulfuric acid
- glucose
[2]

(d) Complete the structure of ethanol to show all atoms and all bonds.



[1]

(e) Ethanol can be made from ethene. Complete the following sentence about the formation of ethanol from ethene using words from the list below.

carbonate catalyst
hydrogen proton steam

Ethanol can be made by reacting ethene with ..................................... in the presence of a ..................................... .
[2]

When sodium hydrogen carbonate is heated at 60 °C, carbon dioxide is given off.
(a) (i) Complete the equation for this reaction.
......NaHCO$_3$ $\rightarrow$ Na$_2$CO$_3$ + CO$_2$ + ..............
(ii) What type of chemical reaction is this?
Tick one box.
[Box] addition
[Box] neutralisation
[Box] oxidation
[Box] thermal decomposition


(b) An aqueous solution of sodium hydrogen carbonate is slightly alkaline.
Which one of the following pH values is slightly alkaline?
Put a ring around the correct answer.
pH 2    pH 7    pH 8    pH 13

(c) Baking powder contains sodium hydrogen carbonate and crystals of a weak acid.
When water is added, the acid reacts with the sodium hydrogen carbonate.
(i) Complete the general equation for the reaction of an acid with a carbonate.
acid + carbonate $\rightarrow$ carbon dioxide + ............................. + .............................
(ii) The diagram below shows bread baked with and without the addition of baking powder.
All other conditions were kept the same.

[Diagram]
baked without baking powder
baked with baking powder

Why is the bread baked with baking powder bigger?
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(iii) Explain why the sodium hydrogen carbonate used in breadmaking must be pure.
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(d) The diagram shows the arrangement of carbon dioxide molecules at $-25^{\circ}$C and 100 atmospheres pressure.

[Diagram]
represents a molecule of carbon dioxide

What is the state of carbon dioxide under these conditions?
Use the kinetic particle theory and the information in the diagram to explain your answer.
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A student investigated the rate of reaction of zinc with dilute hydrochloric acid.

$\text{Zn(s) + 2HCl(aq) } \rightarrow \text{ ZnCl}_2\text{(aq) + H}_2\text{(g)}$

(a) Complete the labelling of the apparatus by filling in the two boxes.


[2]

(b) The student carried out the reaction at 20°C using small pieces of zinc. She measured the volume of hydrogen given off as the reaction proceeded.



(i) Describe how the volume of hydrogen changes with time.

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(ii) At what time did the reaction stop?

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[1]

(iii) What volume of gas was produced over the first two minutes of the reaction?

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[1]

(iv) On the graph above draw a line to show how the volume of hydrogen changes when the reaction was carried out at 30°C. All other conditions remain the same.

[2]

(c) How does the rate of reaction change when larger pieces of zinc are used?

All other conditions remain the same.

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[1]

(d) Molten zinc chloride can be electrolysed using graphite electrodes.

(i) State the names of the product formed at:

the anode ..............................................................................................
the cathode ...........................................................................................
[2]

(ii) Graphite conducts electricity. Give one other reason why graphite electrodes are used.

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[1]

Cinnamic acid is found in plants called balsams.
The structure of cinnamic acid is shown below.
[Image_1: Structure of cinnamic acid]
(a) On the structure of cinnamic acid above, put a ring around the carboxylic acid functional group. [1]
(b) Cinnamic acid is an unsaturated compound.
(i) What is the meaning of the term *unsaturated*?
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(ii) Describe a test for an unsaturated compound.
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(c) Cinnamic acid reacts with sodium hydroxide to form styrene.
\( \text{C}_6\text{H}_5\text{CH=CHCOOH} + 2\text{NaOH} \rightarrow \text{C}_6\text{H}_5\text{CH=CH}_2 + \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} \)
Complete the word equation for this reaction.
cinnamic acid + sodium hydroxide → styrene + ..............................
.................................... + .............................. [2]
(d) Styrene is used to make the polymer poly(styrene).
Poly(ethene) is also a polymer.
Describe how poly(ethene) is made.
In your answer include the words:
• addition
• ethene
• monomer
• polymerisation
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(e) Balsam flowers contain a mixture of pigments.
(i) Describe how you could obtain a solution of this mixture of pigments from balsam flowers.
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(ii) A student uses chromatography to separate the pigments in balsam flowers. He puts the pigment mixture on a sheet of chromatography paper as well as 5 spots of pure pigments A, B, C, D and E.
The diagram below shows the results after chromatography.
[Image_2: Chromatography results]
Which of the pigments A, B, C, D and E are present in balsam flowers?
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The table shows some properties of aluminium, copper, iron and sodium.

[Table_1]

(a) Which two metals in the table are transition elements? Explain your answer by referring to a specific property of transition elements given in the table.

(b) Use the information in the table to suggest

(i) why overhead electricity cables are made from aluminium with a steel core,

(ii) one reason why sodium is not used for electricity cables.

(c) Cobalt chloride is a transition element compound.

Calcium chloride is a compound of a Group II metal.

Describe one difference between cobalt chloride and calcium chloride.

(d) The table below shows some observations about the reaction of four metals with water or steam.

[Table_2]

Place these metals in order of their reactivity.

(e) When iron is heated with steam, hydrogen is given off.

$$3\text{Fe} + 4\text{H}_2\text{O} \rightleftharpoons \text{Fe}_3\text{O}_4 + 4\text{H}_2$$

(i) What does the sign \(\rightleftharpoons\) mean?

(ii) Describe a test for hydrogen.

(f) Steel is an alloy of iron. Write about alloys of iron.

In your answer refer to:

• the meaning of the term alloy,
• why alloys are used instead of pure iron,
• an example of the use of an alloy of iron.

A teacher placed a few drops of liquid bromine in the bottom of a test-tube containing a solvent.
After 10 minutes, the brown colour of the bromine had spread a little way through the solvent.
After 2 hours, the brown colour had spread throughout the solvent.



(a) Use the kinetic particle theory to explain these observations.
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(b) Bromine is a halogen in Group VII.

The properties of some halogens are given in the table below.

[Table_1]

Use the information in the table to:

(i) Deduce the state of fluorine at −200°C.
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(ii) Describe how the melting point changes down Group VII.
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(iii) Estimate the density of bromine.
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(iv) Deduce the number of completely filled electron shells in an atom of chlorine.
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(c) Aqueous bromine reacts with aqueous potassium iodide to form iodine and potassium bromide.

(i) Complete the equation for this reaction.
\( \text{Br}_2 + 2\text{KI} \rightarrow \text{............} + 2\text{KBr} \)
[1]

(ii) Explain why aqueous bromine does not react with an aqueous solution of potassium chloride.
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(d) Bromine reacts with fluorine to form bromine trifluoride, \( \text{BrF}_3 \).

Calculate the relative molecular mass of bromine trifluoride.

Show all your working.
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