A student carried out a titration to determine the concentration of hydrochloric acid using sodium hydroxide solution. She added 3 drops of phenolphthalein indicator to the acid in the flask. What colour change would she observe at the end point?

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Question

A student carried out a titration to determine the concentration of hydrochloric acid using sodium hydroxide solution. She added 3 drops of phenolphthalein indicator to the acid in the flask. What colour change would she observe at the end point?

Accepted Answer

Colourless to pink — Award 1 mark for correct colour change. Phenolphthalein is colourless in acidic solution and turns pink in alkaline solution. At the end point, when sufficient NaOH has been added to neutralise the acid, the solution becomes slightly alkaline, causing the indicator to turn pink. B is incorrect — this would occur if base was in the flask. C is incorrect — this describes litmus. D is incorrect — this describes methyl orange.

Answer

Pink to colourless

Answer

Blue to red

Answer

Yellow to orange

Answer

Colourless to pink

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