(a)(i) Give the names of two allotropes of sulphur.
(ii) State and explain what is observed when hydrogen sulphide is bubbled through acidified potassium tetraoxomanganatc (VII) solution
(iii) List one product of the reaction of sulphur (IV) oxide with hydrogen sulphide
(b)(i) What are the raw materials for the manufacture of tetraoxosulphate (VI) acid by the contact process?
(ii) Write an equation for the reaction that requires a catalyst in the contact process and state the catalyst used.
(iii) State the observation and the product formed when concentrated \(H_2SO_4\) reacts with each of the following:
I. Copper turnings Ii. A cube of sugar
(c)(i) Give three uses of sodium trioxocarbonate (IV).
(ii) What name is given to reactions of the following type?:
\[
\mathrm{Na_2CO_3 + 10H_2O_{(s)} \xrightarrow{\text{exposure to air}} Na_2CO_3; H_2O_{(S)} + 9H_2O}
\]
(iii) Calculate the solubility of \(Na_2CO_3\) at 25°C, if 2.0 cm\(^3\) of its saturated solution at that temperature gave 1.75g of the anhydrous alt. [C = 12, O = 16, Na = 23].
(a)(i) Two allotropes of sulphur: rhombic (octahedral/alpha) sulphur and monoclinic (prismatic/beta) sulphur.
(a)(ii) When H2S is bubbled through acidified KMnO4, the purple solution is decolourised and a pale yellow precipitate of sulphur forms. H2S is a reducing agent: it reduces Mn7+ (purple) to colourless Mn2+ and is itself oxidised to sulphur.
(a)(iii) Product of SO2 with H2S: sulphur (and water): \(\text{SO}_2 + 2\text{H}_2\text{S} \to 3\text{S} + 2\text{H}_2\text{O}\).
(b)(i) Raw materials for the contact process: sulphur (or a sulphide ore/roasted iron pyrites), air (oxygen) and water.
(b)(ii) Catalysed step: \(2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3\); catalyst: vanadium(V) oxide, V2O5.
(b)(iii) Concentrated H2SO4 with:
- I. Copper turnings (hot): the acid acts as an oxidizing agent; the mixture turns blue, SO2 is evolved and copper(II) tetraoxosulphate(VI) forms: \(\text{Cu} + 2\text{H}_2\text{SO}_4 \to \text{CuSO}_4 + \text{SO}_2 + 2\text{H}_2\text{O}\).
- II. A cube of sugar: the acid acts as a dehydrating agent; the sugar chars to a black spongy mass of carbon: \(\text{C}_{12}\text{H}_{22}\text{O}_{11} \to 12\text{C} + 11\text{H}_2\text{O}\).
(c)(i) Uses of sodium trioxocarbonate(IV) (Na2CO3): in the manufacture of glass; softening of hard water; manufacture of soap and detergents; as washing soda.
(c)(ii) The loss of water of crystallisation on exposure to air is called efflorescence.
(c)(iii) Solubility of Na2CO3 at 25 °C: molar mass Na2CO3 \(= 106\ \text{g mol}^{-1}\).
\[ \text{moles in }2.0\ \text{cm}^3 = \frac{1.75}{106} = 0.0165\ \text{mol} \]
\[ \text{solubility} = \frac{0.0165}{2.0/1000} = 8.25\ \text{mol dm}^{-3} \]
(a)(i) Two allotropes of sulphur: rhombic (octahedral/alpha) sulphur and monoclinic (prismatic/beta) sulphur.
(a)(ii) When H2S is bubbled through acidified KMnO4, the purple solution is decolourised and a pale yellow precipitate of sulphur forms. H2S is a reducing agent: it reduces Mn7+ (purple) to colourless Mn2+ and is itself oxidised to sulphur.
(a)(iii) Product of SO2 with H2S: sulphur (and water): \(\text{SO}_2 + 2\text{H}_2\text{S} \to 3\text{S} + 2\text{H}_2\text{O}\).
(b)(i) Raw materials for the contact process: sulphur (or a sulphide ore/roasted iron pyrites), air (oxygen) and water.
(b)(ii) Catalysed step: \(2\text{SO}_2 + \text{O}_2 \rightleftharpoons 2\text{SO}_3\); catalyst: vanadium(V) oxide, V2O5.
(b)(iii) Concentrated H2SO4 with:
- I. Copper turnings (hot): the acid acts as an oxidizing agent; the mixture turns blue, SO2 is evolved and copper(II) tetraoxosulphate(VI) forms: \(\text{Cu} + 2\text{H}_2\text{SO}_4 \to \text{CuSO}_4 + \text{SO}_2 + 2\text{H}_2\text{O}\).
- II. A cube of sugar: the acid acts as a dehydrating agent; the sugar chars to a black spongy mass of carbon: \(\text{C}_{12}\text{H}_{22}\text{O}_{11} \to 12\text{C} + 11\text{H}_2\text{O}\).
(c)(i) Uses of sodium trioxocarbonate(IV) (Na2CO3): in the manufacture of glass; softening of hard water; manufacture of soap and detergents; as washing soda.
(c)(ii) The loss of water of crystallisation on exposure to air is called efflorescence.
(c)(iii) Solubility of Na2CO3 at 25 °C: molar mass Na2CO3 \(= 106\ \text{g mol}^{-1}\).
\[ \text{moles in }2.0\ \text{cm}^3 = \frac{1.75}{106} = 0.0165\ \text{mol} \]
\[ \text{solubility} = \frac{0.0165}{2.0/1000} = 8.25\ \text{mol dm}^{-3} \]
