Question

3.15: Explain why, if soluble salts are prepared from an acid and an insoluble reactant:

a) Excess of the reactant is added
b) The excess reactant is removed
c) The solution remaining is only salt and water

3.16: Explain why, is soluble salts are prepared from an acid and a soluble reactant:
a) Titration must be used
b) The acid and the soluble reactant are then mixed in the correct proportions
c) The solution remaining, after reaction, is only salt and water.

These are two points in the GCSE specification I do not completely understand. Can anyone help?

Answer 1

Soluble salts can be made by reacting acids with either soluble or insoluble bases.

Making a salt from an alkaliIf you are using an alkali - which is a soluble base - then you need to add just enough acid to make a neutral solution (check a small sample with universal indicator paper).Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.Copper oxide and other transition metal oxides or hydroxides do not dissolve in water. If the base is insoluble, then an extra step is needed to form a salt.You add the base to the warm acid until no more will dissolve and you have some base left over – this is called an ‘excess’. You filter the mixture to remove the excess base, and then evaporate the water in the filtrate to leave the salt behind.