An analytical chemist is preparing a highly pure calibration standard of solid potassium sulfate (K2SO4K_2SO_4K2SO4). The chemist first titrates 25.0 cm3 of potassium hydroxide solution with dilute sulfuric acid, using phenolphthalein as an indicator, to determine the exact volume of acid required for neutralisation. \nTo\nTo\nTo obtain the pure, dry sample of potassium sulfate, the chemist repeats the reaction by mixing the exact volumes of acid and alkali determined from the titration, but this time without adding the phenolphthalein indicator. The chemist then evaporates the water from this second mixture to crystallise the salt.
Explain why the chemist must prepare this second mixture without the indicator, rather than evaporating the mixture from the initial titration, to obtain a pure sample of solid potassium sulfate.
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