(a)(i) Name two gases that could be used to perform the fountain experiment.
(ii) State the physical property which makes the gases suitable for the experiment in (a)(i)
(b)(i) Define each of the following terms: I. solubility; II. saturated solution.
(ii) State two factors that affect the solubility of a solid in a liquid.
(iii) A salt Z of mass 10.2 g was dissolved in 15.4 cm\(^3\) of distilled water at 40°C. Calculate the solubility of Z in moldm\(^3\) at 40°C. [Mr (Z) = 331].
(c)(i) Town water supplies that have passed through iron pipes contain P and Q ions. In the presence of air, P ions are slowly converted to Q ions.
I. Identify P and Q ions. II. Write a balanced equation for the reaction between P ions, hydrogen ions and oxygen to give Q ions and water.
(ii) Explain briefly a test to confirm the purity of water.
(iii) State the effect of:
I. boiling a temporally hard water. II. adding sodium trioxocarbonate (IV) crystals to permanent hard water;
(iv) Write a balanced equation for the process in (c)(iii)I.
(a)(i) Two gases for the fountain experiment: ammonia (NH3) and hydrogen chloride (HCl).
(ii) The property is their very high solubility in water.
(b)(i) I. Solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a stated temperature to form a saturated solution.
II. A saturated solution is one that contains the maximum amount of solute it can dissolve at a given temperature, in contact with undissolved solute.
(ii) Two factors affecting solubility of a solid in a liquid: temperature; the nature of the solute and solvent.
(iii) Mass per dm3 \(= 10.2 \times \dfrac{1000}{15.4} = 662.3\ \text{g dm}^{-3}\).
Solubility \(= \dfrac{662.3}{331} = \mathbf{2.0\ mol\ dm^{-3}}\).
(c)(i) I. P = Fe2+ (iron(II)), Q = Fe3+ (iron(III)).
II. \(4Fe^{2+} + 4H^+ + O_2 \rightarrow 4Fe^{3+} + 2H_2O\)
(ii) Test for purity of water: pure water boils at exactly 100 °C (and freezes at 0 °C) at 1 atmosphere; impurities raise the boiling point.
(iii) I. Boiling temporary hard water removes the hardness (it decomposes the hydrogentrioxocarbonate(IV) to insoluble trioxocarbonate(IV), softening the water). II. Adding sodium trioxocarbonate(IV) crystals to permanent hard water softens it by precipitating the Ca2+/Mg2+ ions as insoluble trioxocarbonate(IV).
(iv) \(Ca(HCO_3)_2 \xrightarrow{heat} CaCO_3 + H_2O + CO_2\)
(a)(i) Two gases for the fountain experiment: ammonia (NH3) and hydrogen chloride (HCl).
(ii) The property is their very high solubility in water.
(b)(i) I. Solubility is the maximum amount of a solute that dissolves in a given amount of solvent at a stated temperature to form a saturated solution.
II. A saturated solution is one that contains the maximum amount of solute it can dissolve at a given temperature, in contact with undissolved solute.
(ii) Two factors affecting solubility of a solid in a liquid: temperature; the nature of the solute and solvent.
(iii) Mass per dm3 \(= 10.2 \times \dfrac{1000}{15.4} = 662.3\ \text{g dm}^{-3}\).
Solubility \(= \dfrac{662.3}{331} = \mathbf{2.0\ mol\ dm^{-3}}\).
(c)(i) I. P = Fe2+ (iron(II)), Q = Fe3+ (iron(III)).
II. \(4Fe^{2+} + 4H^+ + O_2 \rightarrow 4Fe^{3+} + 2H_2O\)
(ii) Test for purity of water: pure water boils at exactly 100 °C (and freezes at 0 °C) at 1 atmosphere; impurities raise the boiling point.
(iii) I. Boiling temporary hard water removes the hardness (it decomposes the hydrogentrioxocarbonate(IV) to insoluble trioxocarbonate(IV), softening the water). II. Adding sodium trioxocarbonate(IV) crystals to permanent hard water softens it by precipitating the Ca2+/Mg2+ ions as insoluble trioxocarbonate(IV).
(iv) \(Ca(HCO_3)_2 \xrightarrow{heat} CaCO_3 + H_2O + CO_2\)
