Question

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 hydrochloric
acid, of concentration 2.00 mol dm-3 (in excess).
The excess acid required 19.7 cm of sodium hydroxide (0.200 mol dm-) 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.
[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.​

Answer 1

Answer:

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Explanation:

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Answer 2

a)

(i)When the molar concentration of an excess reactant is known, the need exists to determine the strength or concentration of an analyte is known as a back titration.

A standard solution of strong acid (e.g., HCl) in excess is required to neutralize the excess amount of your titrant.

This is done to achieve the endpoint easier than a standard titration.

(ii)The neutralization reaction involved in the back titration is :

$\\ NaOH(aq) + HCl(aq) ==> NaCl(aq) + H2O(l)$