UPSC Combined Geo-Scientist, Mains · 2019 · Mains Paper III

Q1(d). Washing the flask walls

Question

Acid drops on the inside neck of a titration flask are washed into the solution with distilled water. Does this affect the result?

Proper washing improves quantitative transfer and does not change the stoichiometric titrant amount required.

The water adds no analyte or titrant equivalents. It merely brings acid already belonging to the sample into the reacting liquid.
Although concentration changes, total acid moles remain the same, so the equivalence volume is unchanged.
Use a modest quantity of clean water and mix thoroughly.
Excessive dilution can reduce endpoint sharpness, but routine wall washing is standard good practice.

The full model answer

As written for the answer booklet: the diagram carries the working, the lines stay short. Read here only; it is not offered as a download.

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