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

The structures of five substances are shown below.
[Image]
Answer the following questions about these substances. Each substance may be used once, more than once or not at all.
(a) Which substance, A, B, C, D or E,
(i) is an element, .................. [1]
(ii) turns damp red litmus paper blue, .................. [1]
(iii) is a salt which contains atoms of three different elements, .................. [1]
(iv) is a compound, whose aqueous solution gives a white precipitate on addition of aqueous silver nitrate, .................. [1]
(v) is an ionic compound, whose aqueous solution gives off ammonia when warmed with aluminium powder and aqueous sodium hydroxide? .................. [1]
(b) (i) Give the name of compound B. ............................................................................................................................. [1]
(ii) Complete the following sentences about compounds A and E using words from the list below.
atoms gas giant ions liquid molecular polymer solid
Compound A is a ......................... at room temperature. It does not conduct electricity because it has a simple .......................... structure. Compound E does not conduct electricity when it is .......................... because its .......................... cannot move. [4]

A student adds an aqueous solution of sodium hydroxide to an aqueous solution of ethanoic acid. She measures the temperature before and after the addition of sodium hydroxide.



(a) (i) Explain how this experiment shows that the reaction is exothermic.
............................................................................................................................................................ [1]

(ii) Complete the formula of ethanoic acid showing all atoms and bonds.

[1]

(iii) The product of the reaction is a salt called sodium ethanoate.
Describe how you would prepare pure, dry crystals of sodium ethanoate from a solution of sodium ethanoate in water.
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(b) Ethanoic acid belongs to the carboxylic acid homologous series.
Which two of the following statements describes the members of the same homologous series?
Tick two boxes.

[ ] They have the same physical properties.
[ ] They have different functional groups.
[ ] They have similar chemical properties.
[ ] They are all inorganic chemicals.
[ ] They have the same functional group.
[2]

(c) Ethanoic acid has similar properties to hydrochloric acid.
What would be observed when a small piece of magnesium is added to aqueous ethanoic acid?
............................................................................................................................................................
............................................................................................................................................................ [2]

Copper(II) sulfate is heated strongly. The products are copper(II) oxide and sulfur trioxide.

$\text{CuSO}_4 \overset{\text{heat}}{\longrightarrow} \text{CuO} + \text{SO}_3$

(a) (i) What type of reaction is this? Tick one box.
Addition □
Neutralisation □
Oxidation □
Thermal decomposition □ [1]

(ii) Sulfur trioxide is an acidic gas.
What precautions must be taken when heating copper(II) sulfate in the laboratory?
..........................................................................................................................................
.......................................................................................................................................... [1]

(iii) The diagram below shows the arrangement of sulfur trioxide molecules at 30°C.



What is the state of sulfur trioxide at 30°C?
Use the information in the diagram to explain your answer.
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.......................................................................................................................................... [3]

(b) Sulfur trioxide dissolves in water to form sulfuric acid.

(i) Complete the symbol equation for this reaction.
$\text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{..................}$ [1]

(ii) Sulfuric acid is strongly acidic.
Which one of the following pH values is strongly acidic?
Put a ring around the correct answer.
pH 1 pH 6 pH 7 pH 9 pH 13 [1]

(c) Copper(II) oxide is a solid.
An aqueous solution of copper(II) sulfate can be made by heating excess copper(II) oxide with dilute sulfuric acid.
Draw a labelled diagram of the apparatus you would use to separate the excess copper(II) oxide from the solution.
..........................................................................................................................................
[2]

(d) Anhydrous copper(II) sulfate can be used to test for water.

$\text{CuSO}_4(s) + 5\text{H}_2\text{O}(l) \rightleftharpoons \text{CuSO}_4·5\text{H}_2\text{O}(s)$

(i) What is the meaning of the symbol $\rightleftharpoons$ ?
.......................................................................................................................................... [1]

(ii) Give the colour change when water is added to anhydrous copper(II) sulfate.
from .................................................... to .................................................... [2]

A student investigated the reaction of zinc carbonate with hydrochloric acid.
$$\text{ZnCO}_3(s) + 2\text{HCl}(aq) \to \text{ZnCl}_2(aq) + \text{CO}_2(g) + \text{H}_2\text{O}(l)$$
She measured the decrease in mass of the reaction mixture with time.
(a) Explain why the mass of the reaction mixture decreased with time. [1]
.................................................................................................................................

(b) The student carried out the reaction at 20 °C using small pieces of zinc carbonate. The graph below shows the results.
(i) Describe how the mass of the reaction mixture changes with time. [2]
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.................................................................................................................................
(ii) How long did it take for the reaction to stop? [1]
..................... s
(iii) Calculate the decrease in mass of the reaction mixture in the first 20 seconds of the reaction. [1]
..................... g
(iv) On the grid above, draw a line to show how the mass of the reaction mixture changes when the experiment is carried out at 30 °C and all other conditions remain the same. [2]
(v) How does the rate of this reaction change when larger pieces of zinc carbonate are used? [1]
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(c) The zinc chloride formed in this reaction is a salt.
(i) Give the name of another compound of zinc which, when reacted with hydrochloric acid, makes zinc chloride. [1]
.................................................................................................................................
(ii) Molten zinc chloride can be electrolysed using graphite electrodes.
Give the name of the products formed at
the anode, ........................................................................................................
the cathode, ..................................................................................................... [2]

(a) (i) On the formula above, put a ring around an alcohol functional group. [1]
(ii) How many different elements are there in one molecule of linalool? [1]
(iii) How many carbon atoms are there in one molecule of linalool? [1]
(iv) Linalool is an unsaturated compound. What feature in the formula of linalool shows that it is an unsaturated compound? [1]

(b) Linalool can be extracted from coriander seeds. The following statements are about the procedure for extracting linalool from coriander seeds.
A Distil the solution.
B Add a solvent to the ground up seeds.
C Grind the coriander seeds.
D Filter off the solid from the solution.
E Stir the mixture, then it leave for 24 hours.
(i) Put the statements A, B, C, D and E in the correct order. The first one has been done for you. [2]
(ii) On what physical property does distillation depend? [1]

(c) Petroleum is a mixture of hydrocarbons which can be separated into useful fractions by fractional distillation. The diagram below shows a fractional distillation column.

(i) On the diagram above, put
• a letter X to show where the temperature in the column is lowest, [1]
• a letter H to show where the fraction containing molecules with the highest relative molecular mass exits the column. [1]
(ii) Give one use of the naphtha fraction. [1]

(d) Methane is a hydrocarbon present in natural gas.
(i) Give one other source of methane. [1]
(ii) Give one reason why scientists are concerned about the increasing amount of methane in the atmosphere. [1]
(iii) To which homologous series does methane belong? [1]

The table below shows the properties of some non-metallic elements, A, B, C and D.

[Table_1]

(a) (i) Which two elements are giant covalent structures? Give a reason for your answer.
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........................................................................................................................................................... [2]

(ii) Which element is carbon in the form of graphite? Give a reason for your answer.
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........................................................................................................................................................... [2]

(iii) Which element is chlorine?
........................................................................................................................................................... [1]

(b) When aqueous chlorine is added to aqueous potassium bromide, the solution turns orange. An aqueous solution of bromine and potassium chloride is formed.
Describe and explain what happens when aqueous bromine is added to separate solutions of aqueous potassium chloride and aqueous potassium iodide.
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(c) Chlorine is used in water treatment.
Explain why.
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(d) Complete the diagram below to show the arrangement of electrons in a molecule of chlorine.

[2]

(e) Chlorine reacts with indium, In, to form a chloride with the formula shown below.



(i) Give the molecular formula for this chloride.
........................................................................................................................................................... [1]

(ii) How many protons does indium have in its nucleus?
Use the Periodic Table to help you.
........................................................................................................................................................... [1]

Many flowers produce volatile oils. These oils are responsible for the sweet scent (perfume) of many flowers.
(a) What does the term volatile mean?........................................................................................................................................................................................ [1]

(b) A teacher placed some highly-scented flowers at the front of the class. At first, the students at the back of the class could not smell the scent. After two minutes they could smell the scent.
Use the kinetic particle theory to explain these observations........................................................................................................................................................................................ [3]

(c) Many plant oils are unsaturated hydrocarbons. Alkenes are also unsaturated hydrocarbons. The table shows some properties of four alkenes.
[Table]
(i) How does the boiling point of these alkenes change as the number of carbon atoms in the alkene increases?........................................................................................................................................................................................ [1]
(ii) Why is it difficult to predict the melting point of butene?........................................................................................................................................................................................ [1]
(iii) The relative molecular mass of each alkene differs from the next by 14. Which group of atoms is responsible for this difference? Tick one box.
CH₄ □
CH₃ □
CH₂ □
CH □
[1]
(iv) Complete the word equation for the complete combustion of ethene.
ethene + ....................... → carbon dioxide + ....................... [2]

(d) A radioactive isotope of carbon called carbon-14 can be used to date old pieces of cloth.
(i) What is meant by the term isotope?........................................................................................................................................................................................ [1]
(ii) Carbon-14 contains 8 neutrons and 6 protons. The symbol for carbon-14 can be written as $^14_6\text{C}$.
Write the symbol for carbon-12 in a similar way........................................................................................................................................................................................ [1]