(a)(i) Explain what is meant by saturated solution
(ii) Describe in outline, a suitable procedure for preparing a saturated solution of sodium trioxonitrate(V) at 30°C.
(ii) State two techniques that can be used to recover crystals of sodium trioxonitrate(V) from its saturated solution.
(b) 1.0dm\(^3\) of an aqueous solution at 90°C contains 404g of potassium trioxonitrate(V) and 245g of potassium trioxochlorate (V).
(i) Determine which of the two salts will separate out when the solution is cooled to 60°C. N = 14. O = 16, CI = 35.5, K = 39; Solubility of KNO\(_3\) in water at 60\(^o\)C = 5.14 mol.dm\(^{-3}\), Solubility of KCIO\(_3\) in water at 60°C = 1.61 mol.dm\(^{-3}\)
(ii) Calculate the mass of salt that will separate out at 60°C
(c)(i) List two salts which cause hardness of water.
(ii) Explain why temporary hardness of water result in the furring of kettle.
Explanation
(a)(i) A saturated solution is one which will not dissolve any more of the solute at the given temperature in the presence of crystals of the solute.
(ii) Preparation: To a given volume of distilled water at a temperature above 30°C add NaNO\(^3\) crystals with stirring until no more dissolves, cool to 30°C and decant the clear solution on top
(iii) The two techniques are
(a) Evaporation to dryness
(b) Crystallization]
(b(i) Concentration of solutinn. KNO\(_3\) = \(\frac{404}{101}\) = 4.0mol dm\(^3\)
KClO\(_3\) = \(\frac{245}{122.5}\) = 2.0mol dm\(^3\)
From the information provided KCIO\(_3\) will crystallize out at 101 60°C
while KNO\(_3\) will remain in solution since its solubility at 60°C (5.14 mol dm\(^{-3}\)) is higher than the amount in solution.
(ii) Excess salt = (2.0 -1.61) = 0.39 mole. Mass that will separate = 0.39 x 122.5 = 47.78g
(c)(i) Two salts which cause hardness of water are
(a) Calcium hydrogen trioxocarbonate (iv) Ca(HCO\(_3\))\(_2\).
(b) Calcium tetraoxosulphate(VI) CaSO\(_4\).
(ii) If temporary hard water is boiled in kettle the calcium hydrogen trioxocarbonate(IV) salt causing the hardness decomposes forming the insoluble calcuim trioxocarbonate(iv) which coats the inside of the kettle;
Ca(HCO\(_3\))\(_{2(aq)}\) -> CaCO\(_3\) + H\(_2\)O\(_{(l)}\) + CO\(_{2(g)}\) Soluble insolubl
soluble insoluble