The answer is a But please explain why 22. Methyl red is used as an indicator in

Question

The answer is a But please explain why 22. Methyl red is used as an indicator in a titration of 0.10 M NaOH with 0.10 M HCN. If you depend upon this indicator to complete the titration, will the titration be under- titrated or over-titrated or is it an appropriate indicator? Under-titrated since the pH at the equivalence point is higher than the endpoint. Under-titrated since the pH at the equivalence point is lower than the endpoint. Over-titrated since the pH at the equivalence point is higher than the endpoint. Over-titrated since the pH at the equivalence point is lower than the endpoint. An appropriate indicator since the pH at the equivalence point is about the same as the endpoint. a. b. c. e.

Explanation / Answer

PH range of methyl red = 4.8 - 6.0

as this range is less than 7.0. so this is not a suitablle indicator because here HCN is weak acid and NaOH is strong base.

NaOH + HCN...........> NaCN + H2O

at equivalence point, salt (NaCN) hydrolysis occurs.

CN- + H2O..........> OH- + HCN

as OH- ion produce.

Hence PH at equivalence point is greater than 7.

indicator shows the end point at PH range 4.6 - 6.0 but PH at equivalence point is >7.

so option A is the answer.

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