(a) State the role of each of the following substances in the treatment of river water for town supply (i) Sand bed. (ii) Alum (iii) Chlorine
(b)(i) Give three major uses of H(_2)SO(_4)
(ii) Explain the following observation: A strip of blue litmus paper dropped into concentrated H(_2)SO(_4) becomes charred whereas in dilute H(_2)SO(_4), it turns red and is not charred.
(iii) Write an equation to show how concentrated H(_2)SO(_4) reacts with zinc.
(c)(i) List two gaseous pollutants that can be generated by burning coal.
(ii) Explain why coal burns more easily when it is broken into pieces than when it is in lump form.
(ii) What gas is responsible for most of the explosions in coal mines?
(iv) Name: the non-volatile residue left behind after the destructive distlillation of coal
(d)(i) What is meant by allotropy?
(ii) Name two crystalline allotropes of carbon
(iii) Name two elements apart from carbon, which exhibit allotropy
(iv) It is now known that carbon has an allotropic form called fullerene, containing molecules of formula C(_{60}). Calculate the mass of one mole of these molecules [C = 12]
Explanation
(a) In the treatment of river water for town supply
(i) Sand bed is used for filtration
(ii) Alum is used for coagulation of suspended particles
(iii) Chlorine is used for killing bacteria/for sterilizing the water.
(b)(i) Major uses H(_2)SO(_4).
-For the manufacture of fertilizers, pigments, plastics, cellulose films.
-As an electrolyte in batteries
-As a dehydrating agent
-For cleaning metals.
-Petroleum refining
(ii) Blue litmus paper is charred in Conc. H(_2)SO(_4) because it is dehydrated. In dilute H(_2)SO(_4), it turns red as a result of the presence of H(_3)O(^+). It is not charred because dilute H(_2)SO(_4) does not dehydrate
(iii) Reaction of concentrated H(_2)SO(_4) with zinc. Zn + 2H(_2)SO(_4) -> ZnSO(_4) + SO(_4)+ 2H(_2)O.
(c)(i) Gaseous pollutant that can be generated by burning coal are SO(_2), NO2(_2), CO.
(ii) Coal burns more easily when it is broken into pieces than when it is in lump form becauce the pieces have a larger surface area and the larger this is, the higher the rate of reaction. This could also be explained in terms of particle size.
(iii) The gas that is respo:isible for most of the explosions in coal mines is methane (CH(_4))
(iv) Coke is the non-volatile residue of the destructive distillation of coal.
(d)(i) Allotropy is the existence of two or more forms of an element in the same physical state?
(ii) The two crystalline allotropes of carbon are graphite and diamond.
(iii) Other elements which exhibit allotropy are: Sulphur, phosphorus, oxygen, tin
(iv) to calculate the mass of one mole of the fullerene C(_{60}) – (12 x 60)g = 720g.