(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).
(a)(i) A suitable drying agent for carbon(IV) oxide is concentrated tetraoxosulphate(VI) acid, \(H_2SO_4\). (Fused calcium chloride is also acceptable; solid NaOH or CaO must not be used because they react with \(CO_2\).)
(ii) To distinguish carbon(II) oxide from carbon(IV) oxide, bubble each gas through limewater (calcium hydroxide solution): carbon(IV) oxide turns limewater milky, whereas carbon(II) oxide does not. (Alternatively, carbon(II) oxide burns with a blue flame; carbon(IV) oxide does not burn.)
(b)(i) Oxygen and nitrogen are obtained industrially by the fractional distillation of liquid air: air is filtered, and its carbon(IV) oxide and water vapour removed; it is then compressed and cooled repeatedly until it liquefies; the liquid air is allowed to warm in a fractionating column, and because nitrogen has a lower boiling point (\(-196^{\circ}C\)) it boils off first, leaving oxygen (b.p. \(-183^{\circ}C\)) behind.
(ii) Using a lighted splint: oxygen relights (rekindles) a glowing splint and makes a lighted splint burn more brightly, whereas nitrogen puts out (extinguishes) a lighted splint.
(c)(i) Bauxite is preferred as the ore for aluminium extraction because it is the most abundant and richest ore of aluminium (high proportion of aluminium oxide) and is cheap and readily available.
(ii) Two main impurities in bauxite: iron(III) oxide (\(Fe_2O_3\)) and silicon(IV) oxide/silica (\(SiO_2\)).
(iii) Sodium hydroxide solution dissolves the amphoteric aluminium oxide (forming soluble sodium aluminate), leaving the insoluble impurities behind to be filtered off; that is, it purifies the ore.
(iv) It is difficult to extract aluminium by chemical reduction of its oxide because aluminium is very reactive and high in the electrochemical series; it has a strong affinity for oxygen, so ordinary reducing agents (carbon, carbon(II) oxide, hydrogen) cannot reduce aluminium oxide. Electrolysis is used instead.
(v) \[Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O\]
(d)(i) Sodium chloride does not conduct electricity at 25\(^{\circ}\)C because in the solid state the ions are held firmly in fixed positions in the crystal lattice and are not free to move. Between 801\(^{\circ}\)C and 1413\(^{\circ}\)C it is molten, so the ions become free (mobile) and can move to carry the current.
(ii) Sodium is stored under paraffin oil because it is very reactive and would otherwise react rapidly with the oxygen and moisture of the air; the paraffin excludes air and water from the metal.
(e)(i) When aqueous sodium trioxocarbonate(IV) is added to a solution containing iron(III) ions, a reddish-brown precipitate (of iron(III) hydroxide) is formed, with effervescence (bubbles) of carbon(IV) oxide.
(ii) \[2FeCl_3 + 3Na_2CO_3 + 3H_2O \rightarrow 2Fe(OH)_3 + 6NaCl + 3CO_2\]
(a)(i) A suitable drying agent for carbon(IV) oxide is concentrated tetraoxosulphate(VI) acid, \(H_2SO_4\). (Fused calcium chloride is also acceptable; solid NaOH or CaO must not be used because they react with \(CO_2\).)
(ii) To distinguish carbon(II) oxide from carbon(IV) oxide, bubble each gas through limewater (calcium hydroxide solution): carbon(IV) oxide turns limewater milky, whereas carbon(II) oxide does not. (Alternatively, carbon(II) oxide burns with a blue flame; carbon(IV) oxide does not burn.)
(b)(i) Oxygen and nitrogen are obtained industrially by the fractional distillation of liquid air: air is filtered, and its carbon(IV) oxide and water vapour removed; it is then compressed and cooled repeatedly until it liquefies; the liquid air is allowed to warm in a fractionating column, and because nitrogen has a lower boiling point (\(-196^{\circ}C\)) it boils off first, leaving oxygen (b.p. \(-183^{\circ}C\)) behind.
(ii) Using a lighted splint: oxygen relights (rekindles) a glowing splint and makes a lighted splint burn more brightly, whereas nitrogen puts out (extinguishes) a lighted splint.
(c)(i) Bauxite is preferred as the ore for aluminium extraction because it is the most abundant and richest ore of aluminium (high proportion of aluminium oxide) and is cheap and readily available.
(ii) Two main impurities in bauxite: iron(III) oxide (\(Fe_2O_3\)) and silicon(IV) oxide/silica (\(SiO_2\)).
(iii) Sodium hydroxide solution dissolves the amphoteric aluminium oxide (forming soluble sodium aluminate), leaving the insoluble impurities behind to be filtered off; that is, it purifies the ore.
(iv) It is difficult to extract aluminium by chemical reduction of its oxide because aluminium is very reactive and high in the electrochemical series; it has a strong affinity for oxygen, so ordinary reducing agents (carbon, carbon(II) oxide, hydrogen) cannot reduce aluminium oxide. Electrolysis is used instead.
(v) \[Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O\]
(d)(i) Sodium chloride does not conduct electricity at 25\(^{\circ}\)C because in the solid state the ions are held firmly in fixed positions in the crystal lattice and are not free to move. Between 801\(^{\circ}\)C and 1413\(^{\circ}\)C it is molten, so the ions become free (mobile) and can move to carry the current.
(ii) Sodium is stored under paraffin oil because it is very reactive and would otherwise react rapidly with the oxygen and moisture of the air; the paraffin excludes air and water from the metal.
(e)(i) When aqueous sodium trioxocarbonate(IV) is added to a solution containing iron(III) ions, a reddish-brown precipitate (of iron(III) hydroxide) is formed, with effervescence (bubbles) of carbon(IV) oxide.
(ii) \[2FeCl_3 + 3Na_2CO_3 + 3H_2O \rightarrow 2Fe(OH)_3 + 6NaCl + 3CO_2\]
