(a) State the conditions necessary for the cracking of long-chain hydrocarbons to produce more gasoline.
(b) State two reasons why metallic objects are electroplated
(c) (i) Explain briefly why calcium oxide cannot be used to dry hydrogen chloride gas. (ii) State one drying agent for hydrogen chloride gas.
(d) Concentrated trioxonitrate (V) acid was added to a solution of iron (II) tetraoxosulphate (VI) and the mixture heated. The mixture turned from pale green to yellow with the evolution of a brown gas. Explain briefly these observations.
(e) (i) Write the equation for the reaction between zinc oxide and
(ii) State which property of zinc oxide is shown by the reaction in (e)(i).
(f) Two isotopes of chlorine are \(^{35}_{17}\)Cl and \(^{37}_{17}\)Cl State one:
similarity; difference between the isotopes.
(g) State the two products formed when chlorine water is exposed to sunlight.
(h) Consider the reaction represented by the following equation:
State the:
species that is undergoing oxidation; oxidizing agent.
(i) What is meant by carbon-12 scale?
(j) State two properties of a chemical system in equilibrium.
Explanation
(a) - high temperatures / stated temperature of 500\(^o\)C or more - catalyst (b) - To prevent corrosion/rusting/tarnishing - To make them shiny/for decoration purpose/beautify/attractive - To make surface harder/thicker - To make more resistant to chemicals - To make it durable - To reduce friction/abrasion (c) (i) Because calcium oxide is basic and hydrogen chloride is acidic ,they will react to form salt and water. (ii) - Fused CaCl\(_2\) - (Conc) H\(_2\)SO\(_4\) (do not accept dil H\(_2\)SO\(_4\)) - Silica gel - Phosphorus(V) oxide/P\(_2\)O\(_5\)
(d) Conc. HNO\(_3\) is a strong oxidizing agent. It oxidizes pale green Fe\(^{2+}\) ions to yellow Fe\(^{3+}\) ions (1) and itself reduced to nitrogen (IV) oxide. (e) (i) I. ZnO(s) + H\(_2\)SO\(_{4(aq)}\) \(\to\) ZnSO\(_{4(aq)}\) + H\(_2\)O\(_{(l)}\) II. ZnO\(_{(s)}\) + 2NaOH\(_{(aq)}\) \(\to\) Na\(_{2}\) Zn(OH)\(_{4 (aq)}\)
OR ZnO + 2NaOH \(\to\) Na\(_2\)ZnO\(_2\) + H\(_2\)O (ii) Amphoterism / Amphoteric properties (f) (i) Same number (17) of protons / same number (17) of electrons/same atomic number (ii) Difference in mass numbers / different number of neutrons / 35Cl has 18 neutrons and 37Cl has 20 neutrons (g) - HCl / hydrochloric acid - O\(_2\) / Oxygen (h) (i) H\(_2\)S (ii) SO\(_2\) (i) It is the mass reference scale in which the atom of the 12C isotope is taken to have twelve units of atomic mass OR It is a scale that uses the 12C isotope as the standardfor comparing the atomic masses of other elements. (j) - The rate of forward reaction equals the rate of backward reaction / The system is dynamic - There is no net change in the concentration of each substance - The equilibrium compositions of the substances can be approached from either reactants or products - Gibb’s free energy/ is zero
