Titration
3 marks · EasyState the colour change you would see when phenolphthalein is used as the indicator and the alkali in the conical flask is just neutralised by the acid from the burette.
Give one reason why phenolphthalein is preferred over universal indicator for titrations.
Name the flask used to hold the solution during a titration.
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(a) Colourless to pale pink (or pink to colourless)
(b) It has a sharp (clear) colour change at endpoint.
(c) Conical flask
Common mistakes: incorrect indicator colour change, misnaming flask
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Marking points
B1 (a) · 1 mark · Correct colour change given: (colourless to) pale pink or pink to colourless for phenolphthalein.
B1 (b) · 1 mark · Accepts 'sharp colour change', 'distinct endpoint', or equivalent with phenolphthalein.
B1 (c) · 1 mark · Correctly names conical flask as the vessel used.
Worked solution
(a) Phenolphthalein changes from pink (alkali) to colourless (acid) when just neutralised.
(b) Phenolphthalein is preferred because its colour change is sharp, so the endpoint is clear.
(c) The flask used is a conical flask.