Answer to Question #254439 in Physical Chemistry for amm

Question

4.06 g of impure magnesium oxide was completely dissolved in 100 cm3 of hydrochloric acid, of concentration 2.00 mol dm-3 (in excess).The excess acid required 19.7 cm3 of sodium hydroxide (0.200 mol dm-3) for neutralisation using 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.a)Why do you have to use excess acid and employ a back titration?write equations for the two neutralisation reactions.b) calculate the moles of hydrochloric acid added to the magnesium oxide.c) calculate the moles of excess hydrochloric acid titrated.d) calculate the moles of hydrochloric acid reacting with the magnesium oxide.e) calculate the moles and mass of magnesium oxide that reacted with the initial hydrochloric acid.f) hence the % purity of the magnesium oxide.g) what compounds could be present in the magnesium oxide that could lead to a false value of its purity? explain

Answer 1

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