Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2014 Summer Zone 3

(a) Choose from the list of compounds below to answer the following questions.

aluminium oxide
calcium carbonate
calcium oxide
copper(II) sulfate
hydrogen chloride
potassium bromide
sodium chloride
sodium hydroxide

Each compound can be used once, more than once or not at all.
Which compound:

(i) reacts with aqueous ammonia to form a light blue precipitate,
................................................................................................................................. [1]

(ii) is formed by the decomposition of limestone,
................................................................................................................................. [1]

(iii) forms an acidic solution when dissolved in water,
................................................................................................................................. [1]

(iv) when electrolysed, gives a red-brown vapour at the anode,
................................................................................................................................. [1]

(v) is an oxide of a metal in Group III of the Periodic Table,
................................................................................................................................. [1]

(vi) is a transition element compound?
................................................................................................................................. [1]

(b) Complete the following sentences about compounds using words from the list below.

chemically different fixed mixed physically similar

A compound is a substance which consists of two or more different elements ............................. combined together.

The properties of a compound are ............................. from those of the elements from which it is formed.

In a compound, the elements are combined in ............................. proportions. [3]

(a) Calcium chloride, CaCl₂, is a salt. Suggest the name of an acid and a base that would react together to make calcium chloride.
acid ................................................
base ................................................

(b) Calcium chloride absorbs water vapour. When calcium chloride is heated, it loses its water of crystallisation. Complete the symbol equation for this reaction. Include the sign for a reversible reaction.
CaCl₂·6H₂O ⇌ CaCl₂ + ...............

(c) A student put some clean iron nails in two test-tubes, as shown in the diagram. She then left the test-tubes for several weeks.

Explain why the nails in tube A did not rust but the nails in tube B rusted.
......................................................

(d) Rust is hydrated iron(III) oxide. What does the (III) in iron(III) oxide refer to? Tick one box.
the oxidation state of the oxygen [ ]
the oxidation state of the iron [ ]
the number of atoms of oxygen in a formula unit of iron(III) oxide [ ]
the number of water molecules in the hydrated iron oxide [ ]

(e) (i) The table describes the ease of reduction of some metal oxides with carbon monoxide.
[Table_1]
Put these metals in order of their reactivity with carbon monoxide.
least reactive ______________ most reactive

(e) (ii) Some metal oxides can be reduced by heating with hydrogen gas.
CuO + H₂ → Cu + H₂O
Explain how this equation shows that copper oxide is being reduced.
......................................................

The diagram shows the best pH ranges for growing different plants.

(a) (i) Which two plants grow best in acidic conditions only?
............................................................ and ............................................................ [1]
(ii) Which pH shown in the diagram above represents a neutral pH?
................................................................................................................................. [1]
(b) (i) Explain why lime is added to acidic soils.
.................................................................................................................................
................................................................................................................................. [2]
(ii) Farmers fertilise soil by adding compounds containing ammonium salts. Explain why adding lime to fertilised soil may cause a loss of nitrogen from the soil.
.................................................................................................................................
................................................................................................................................. [3]
(c) The graphs below show the rate of uptake of potassium and phosphate ions by plant roots at different pH values.

(i) Describe the effect of pH on the rate of uptake of potassium by plant roots.
.................................................................................................................................
................................................................................................................................. [2]
(ii) At which pH value is the rate of uptake of phosphorus by plant roots the highest?
................................................................................................................................. [1]

Chromatography is used to separate a mixture of coloured dyes.
(a) Three different dye mixtures, A, B and C, were spotted onto a piece of chromatography paper. Two pure dyes, X and Y, were also spotted onto the same piece of paper. The diagram below shows the results of the chromatography.

(i) State the name of a piece of apparatus that could be used to spot the dyes onto the paper. ................................................................................................................................................. [1]
(ii) Suggest why the base line was drawn in pencil and not in ink. ................................................................................................................................................. [1]
(iii) Which dye mixture contains both dye X and dye Y? ................................................................................................................................................. [1]
(iv) Which dye mixture does not contain dye X or dye Y? ................................................................................................................................................. [1]
(v) In which mixture, A, B or C, has the greatest number of dyes been separated? ................................................................................................................................................. [1]

(b) The structure of the dye chrysoidine G is shown below.

(i) How many nitrogen atoms are there in a molecule of chrysoidine G? ................................................................................................................................................. [1]
(ii) Complete the table below to calculate the relative molecular mass of chrysoidine G.
[Table_1]
relative molecular mass = .......................... [2]

(c) The fibres in the chromatography paper are polymers.
(i) What is meant by the term polymer? ................................................................................................................................................. [1]
.................................................................................................................................................
(ii) State the chemical name of the polymer formed from ethene. ................................................................................................................................................. [1]

The table shows some properties of the first four carboxylic acids.

[Table_1]

(a) (i) How does the boiling point of these carboxylic acids vary with the number of carbon atoms?
....................................................................................................... [1]

(ii) Suggest a value for:
the boiling point of propanoic acid, ........................................................ °C
the density of butanoic acid. ............................................................... g/cm³
[2]

(iii) Is butanoic acid a solid, liquid or gas at room temperature?
Use the data in the table to explain your answer.
.......................................................................................................
.......................................................................................................
[1]

(b) Complete the diagram below to show the structure of ethanoic acid.
Show all atoms and bonds.


[1]

(c) The concentration of ethanoic acid can be determined by titration using the apparatus shown below.



(i) State the name of the piece of glassware labelled A.
....................................................................................................... [1]

(ii) Liquid B is an alkali.
Which one of the following compounds is also an alkali?
Put a ring around the correct answer.

calcium carbonate
calcium sulfate
sodium chloride
sodium hydroxide
[1]

(iii) Describe how you would carry out this titration.
.......................................................................................................
.......................................................................................................
.......................................................................................................
.......................................................................................................
[2]

Lead(II) bromide is a white solid. Part of the structure of lead(II) bromide is shown below.

(a) Deduce the simplest formula for lead(II) bromide.
........................................................................................................................ [1]

(b) A student electrolysed lead(II) bromide in a fume cupboard using the apparatus shown below.

(i) Why is heat needed for this electrolysis?
........................................................................................................................ [1]
(ii) Suggest the name of a substance that could be used for the electrodes.
........................................................................................................................ [1]
(iii) State the name of the products of electrolysis at:
the anode, .................................................................................................
the cathode. ............................................................................................... [1]

(c) Items can be electroplated with silver using the apparatus shown below.

(i) On the diagram, which letter, A, B, C or D, is the cathode?
........................................................................................................................ [1]
(ii) What would you observe during the experiment at the:
positive electrode, .....................................................................................
negative electrode? .................................................................................. [2]
(iii) The electrolyte used is aqueous silver cyanide, AgCN. Calculate the relative formula mass of silver cyanide. You must show all your working. [2]

Dmitri Mendeleev published his first Periodic Table in 1869. Part of this table is shown below.


(a) (i) What differences are there between Mendeleev's table and the Periodic Table we use today?
..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... [4]

(a) (ii) State the names of any two elements in the table above which exist as diatomic molecules.
.................................................. and .......................................................... [1]

(b) Titanium is a transition element. Sodium is a metal in Group I of the Periodic Table. State three differences in the physical properties of titanium and sodium.
1 .....................................................................................................................
2 .....................................................................................................................
3 ..................................................................................................................... [3]

(c) Titanium(IV) oxide reacts with a mixture of chlorine and carbon. The products are titanium(IV) chloride, TiCl₄, and a gas which turns limewater milky. Complete the symbol equation for this reaction.
TiO₂ + .....Cl₂ + C → TiCl₄ + ............ [2]

(d) Titanium is extracted from titanium(IV) chloride by reduction with molten sodium in the presence of argon. Suggest why this reaction is carried out in the presence of argon.
..................................................................................................................... ..................................................................................................................... [2]

Sodium sulfate is a solid with a high melting point. Sodium sulfate conducts electricity when molten but not when solid.
(a) What type of structure is sodium sulfate? Tick one box.
structure of separated atoms □
simple molecular structure □
giant ionic structure □
giant covalent structure □ [1]
(b) Describe a test for sulfate ions.
test ............................................................
result ............................................................ [2]
(c) Describe how simple distillation is used to separate water from an aqueous solution of sodium sulfate.
In your answer, refer to:
• the apparatus used,
• changes in state,
• differences in boiling points.
You may use a diagram. [5]
(d) What would you observe when a piece of blue cobalt chloride paper is dipped into water? [1]
(e) Describe how impure water is treated so that it can be used for drinking. [2]