(a) What is the structure of:
(i) graphite:
(ii) diamond
(ii) Explain briefly why diamond is hard and a non-conductor of electricity while graphite is soft and an electrical conductor,
(b)i. State what is achieved at each of the following stages in the purification of town water supply:
– aeration;
– screening
– sedimentation.
(ii) Name two substances responsible for hardness in water.
(iii) State two methods for the removal of hardness in water.
(iv) Give one disadvantage of hard water
(c)i). Describe briefly the extraction of tin from its ore.
(ii) Write a balanced chemical equation for the reaction.
(iii) Write an equation for the reaction of tin with:
– oxygen;
– chlorine.
Explanation
(a) Graphite:-hexagonal: Diamond:-letrahedral/octahedral
(ii) Explain briefly why diamond is hard and a non-conductor of electricity while graphite is soft and an electrical conductor: n diamond each carbon atom is covalently bonded to four other carbon atoms forming an interlocking three dimens1onal network hence the hardness. Each of the four valence electrons is localized in a covalent bond hence there are no free mobile electrons, while in graphite each carbon atom is bonded to three other carbon atoms forming large sheets with van der Waal's force between the sheets which can easily slide over one another. One of the valence electrons of each atom is delocalized in a covalent bond and can act as a conductor of electricity OR Diamond is hard because it has a rigid/three-dimensional structure. It has no free/ mobile electrons hence it does not conduct electricity. Graphite has a layered structure held together by weak van der Waal's forces hence it is soft. It conducts electricity because it has free/ mobile electrons.
(bi) State what is Achieved at each of the Following Stages in the Purification of Water for Town Supply:
- Aeration- removes odor/kills bacteria.
- Screening- removal of suspended dirt
- Sedimentary- removal of suspended dirt particles after coagulation.
(ii) Name two Substances Responsible for Hardness in Water:
- Calcium hydrogen trioxocarbonate (IV).
- MagnesIum hydrogen triOxocarbonate(IV).
- Magnesium chloride.
- Magnesium tetraOxOSulphate( Vl).
- Calcium tetraoxosulphate (VI).
- Iron (lI) hydrogen trioxocarbonate(IV).
- Calcium chloride.
- Iron(Il) tetraoxosulphate(VI)
(iii) State two Methods for the Removal of Hardness in Water:
- By adding washing soda (Na\(_{2}\)CO\(_{3}\)). Adding (CaCOH)\(_{2}\) /lime water.
- Using ion-exchange resin / permutit/ zeolite.
- Boiling/ distillation
(iv) Give one Disadvantage of Hard Water:
- Furring of kettle/pipes causes blockage leading to power wastage/ scales in the boiler.
- Soap is wasted/ forms scums
- Cannot be used in dyeing/ tanning
- Not suitable for laundry.
- Not suitable for textile industry
(c) Describe Briefly the Extraction of Tin from its Ores:
(i) The ore is concentrated/crushed and washed with water, it is then roasted in air to remove impurities. The product is mixed with charcoal/carbon /coke and heated to reduce the oxide. it is then refined to obtain pure tin.
(ii) SnO\(_{2(s)}\) + 2C\(_{(s)\) \(\implies\) Sn\(_{(l)}\) + 2CO\(_{(g)}\)
(iii) (I) Sn\(_{(s)}\) + O2\(_{(g)}\) \(\implies\) Sn\(_{2(s)}\)
(II) Sn\(_{(s)\) + 2Cl\(_{2(g)}\) \(\implies\) SnCl\(_{4}\)