(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]
(a) (i) Sand bed: filtration, removes suspended solid particles. (ii) Alum: coagulant, makes fine suspended/colloidal particles clump together and settle. (iii) Chlorine: sterilization, kills harmful bacteria and micro-organisms.
(b)(i) Three uses of H2SO4: manufacture of fertilizers (e.g. ammonium sulphate); manufacture of detergents; as the electrolyte in lead-acid accumulators (car batteries).
(ii) Concentrated H2SO4 is a powerful dehydrating agent: it removes hydrogen and oxygen (as water) from the litmus (a carbohydrate), leaving black carbon, so the paper is charred. Dilute H2SO4 is not a dehydrating agent; it is simply acidic, ionizing to give H+ ions that turn blue litmus red without charring.
(iii) Zn + 2H2SO4(conc) → ZnSO4 + SO2 + 2H2O (hot, concentrated).
(c)(i) Two gaseous pollutants from burning coal: sulphur(IV) oxide (SO2) and carbon(II) oxide (CO). (ii) Broken coal has a much larger surface area exposed to oxygen than a lump, so more coal is in contact with air and the rate of burning (frequency of effective collisions) increases, making it burn faster. (iii) Methane (firedamp) is responsible for most explosions in coal mines. (iv) The non-volatile residue from destructive distillation of coal is coke.
(d)(i) Allotropy is the existence of an element in two or more different forms in the same physical state. (ii) Diamond and graphite. (iii) Two other elements showing allotropy: sulphur and phosphorus. (iv) Mass of one mole of C60 = 60 × 12 = 720 g.
(a) (i) Sand bed: filtration, removes suspended solid particles. (ii) Alum: coagulant, makes fine suspended/colloidal particles clump together and settle. (iii) Chlorine: sterilization, kills harmful bacteria and micro-organisms.
(b)(i) Three uses of H2SO4: manufacture of fertilizers (e.g. ammonium sulphate); manufacture of detergents; as the electrolyte in lead-acid accumulators (car batteries).
(ii) Concentrated H2SO4 is a powerful dehydrating agent: it removes hydrogen and oxygen (as water) from the litmus (a carbohydrate), leaving black carbon, so the paper is charred. Dilute H2SO4 is not a dehydrating agent; it is simply acidic, ionizing to give H+ ions that turn blue litmus red without charring.
(iii) Zn + 2H2SO4(conc) → ZnSO4 + SO2 + 2H2O (hot, concentrated).
(c)(i) Two gaseous pollutants from burning coal: sulphur(IV) oxide (SO2) and carbon(II) oxide (CO). (ii) Broken coal has a much larger surface area exposed to oxygen than a lump, so more coal is in contact with air and the rate of burning (frequency of effective collisions) increases, making it burn faster. (iii) Methane (firedamp) is responsible for most explosions in coal mines. (iv) The non-volatile residue from destructive distillation of coal is coke.
(d)(i) Allotropy is the existence of an element in two or more different forms in the same physical state. (ii) Diamond and graphite. (iii) Two other elements showing allotropy: sulphur and phosphorus. (iv) Mass of one mole of C60 = 60 × 12 = 720 g.
