(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