(a)(i) Name a suitable drying agent for the preparation of carbon (IV) oxide in the laboratory. (ii) Using one chemical test, distinguish between carbon (II) oxide and carbon (IV) oxide.
(b)(i) Describe briefly how oxygen and nitrogen could be obtained separately from air on an industrial scale (ii) State how a lighted splint can be used to distinguish between samples of oxygen and nitrogen.
(c)(i) Give one reason why bauxite is usually preferred as the ore for the extraction of aluminium. (ii). List two main impurities. usually present in bauxite. (iii) State the function of sodium hydroxide solution in the extraction of aluminium from its ore. (iv) Explain briefly why it is difficult to extract aluminium by chemical reduction of aluminium oxide (v) Write an equation for the reaction of aluminium oxide with aqueous sodium hydroxide.
(d) (i) The melting and boiling points of sodium chloride are 801 °C and 141.3 °C respectively. Explain briefly why sodium chloride does not conduct electricity at 25°C but does so between 801 °C and 1413 °C. (ii) State the reason why sodium metal is stored under paraffin oil in the laboratory.
(e)(i) State what would be observed when aqueous sodium trioxocarbonate(IV) is added to a solution containing iron (III) ions (ii) Write a balanced equation for the reaction in (e)(i).
Explanation
(a) (i) Concentrated tetraoxosulphate (vi) acid fused calcuim chloride. (ii) Pass or bubble each gas into lime water, if lime water turns milky then CO, is present if no reaction then CO is present.
(b) (i) –Atmospheric air is compressed and cooled to liquefy it. – The liquefied air undergoes fractional distillation. – Nitrogen boils out first at – 196°C followed by oxygen at – 183°C. (ii) – Splint burns brighter / continues to burn in oxygen. Splint is extinguished in nitrogen
(c) (i) – Bauxite is more abundant than any other ore. – Bauxite has less percentage of silicates as impurity. (ii) . – iron (III) oxide. – Trioxosilicates(IV) / silica / sand. (iii) To dissolve the aluminium oxide so that the impurities can be filtered off (iv) Aluminium is very reactive to be reduced by the eommon reducing agenfleoaction. (v) Al\(_2\)O\(_3\) + 2NaOH \(\to\) 2NaAlO\(_2\) +H\(_2\)O or Al\(_2\)O\(_2\) + 2NaOH + 3H\(_2\)O --> 2NaAl(OH)\(_4\) (d) (i) The ions are not free at 25°C since sodium chloride is in the solid state but between 801°C and 1413°C the ions are free / mobile since it is now in the molten / liquid state. (ii) Sodium metal is very reactive with air/ it is easily oxidised in air / tarnishes easily.
(e) (i) Brown precipitate / reddish brown / orange solid formed (ii) 3Na\(_2\)CO\(_{3(aq)}\) + 2Fe\(^{3+}\) --> Fe\(_{2}\) (CO\(_3\))\(_{3(s)}\) + 6Na\(^{+}\)
