Question 5
(a)
- Define the term hardness of water.
- Give two advantages of hard water.
- Give two disadvantages of hard water.
- State how each of the following procedures can be carried out in the laboratory:
- Removal of sediment in a sample of water;
- Softening temporarily hard water without heating it.
[8 marks]
(b)
(i) Write an equation for the laboratory preparation of chlorine.
(ii) Name the products formed when chlorine reacts with hot concentrated sodium hydroxide solution.
[6 marks]
(c)
(i) Give two properties of copper which make it useful for ornamental work.
(ii) Give two uses of copper (II) tetraoxosulphate (VI).
(iii) Name one alloy of:
- copper;
- aluminium.
(iv) State the reason why metals are good conductors of electricity.
[7 marks]
(d)
(i)Give two uses of trioxonitrate (V) acid.
(ii) In the preparation of trioxonitrate (V) acid in the laboratory from trioxonitrate (V) salts, state:
- what other reagent is required?
- the reason why an all-glass apparatus must be used.
[4 marks]
Observation
In part (a), majority of the candidates were able to define the term hardness of water and gave the advantages of hard water.
In part (b), majority of the candidates could not write an equation for the laboratory preparation of chlorine.
In part (c), majority of the candidates were able to give two properties of copper which make it useful for ornamental work. In addition to this, they were able to name one alloy of copper and aluminium.
In part (d), majority of the candidates were able to give two uses of trioxonitrate (V) acid and gave the reason why an all-glass apparatus must be used.
The expected answers include:
(a)
(b)
(c)
(i)
- malleable / ductile
- lustrous / attractive
- relatively unreactive / does not react with moisture or air / resistant to
corrosion
(ii)
- Fungicide / fumigant
- Purification of gases
- Testing for water
- Disinfectant in reservoirs / swimming pools
- Electroplating
- Preservatives
- Dyeing
(iii)
I. copper : - brass / bronze / duralumin / silver coinage
II. aluminium:- duralumin / magnalumin / Alnico
(iv) Because they have mobile / free electrons
(d) (i) - used as rocket fuel
- manufacture of dynamites / explosives
- manufacture of dyestuff
- as an oxidizing agent
- nitrating agent / formation of nitrates
- solvent for gold and platinium
- manufacture of drugs
(ii) I. Conc. H2SO4 Do not accept dilute H2SO4
II. the acid (vapour) formed will rapidly attack the cork and rubber /
attack any other material