Q2) Magnesium oxide is not very soluble in water, and is difficult to titrate directly. Its purity can be determined by use of a 'back titration' method.4.06 g of impure magnesium oxide was completely dissolved in 100 cm3 of hydrochloricacid, of concentration 2.00 mol dm-3 (in excess).The excess acid required 19.7 cm of sodium hydroxide (0.200 mol dm-) for neutralisationusing phenolphthalein indicator and the end-point is the first permanent pink colour.This 2nd titration is called a 'back-titration', and is used to determine the unreacted acid.[atomic masses: Mg = 24.3, 0 = 16](a) (i) Why do you have to use excess acid and employ a back titration?(ii) write equations for the two neutralisation reactions.

Q2) Magnesium oxide is not very soluble in water, and is difficult to

1.	Q2) Magnesium oxide is not very soluble in water, and is difficult to titrate directly. Its purity can be determined by use of a 'back titration' method.4.06 g of impure magnesium oxide was completely dissolved in 100 cm3 of hydrochloricacid, of concentration 2.00 mol dm-3 (in excess).The excess acid required 19.7 cm of sodium hydroxide (0.200 mol dm-) for neutralisationusing phenolphthalein indicator and the end-point is the first permanent pink colour.This 2nd titration is called a 'back-titration', and is used to determine the unreacted acid.[atomic masses: Mg = 24.3, 0 = 16](a) (i) Why do you have to use excess acid and employ a back titration?(ii) write equations for the two neutralisation reactions.
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