Question

A testtube contains solution of NaOH and Phenolphthalein. Why the colour

of the solution changes when HCl in added to it.
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Answer 1

Answer:

⭐Since, phenolphthalein is an artificial indicator, it gives pink colour in a basic solution and remains colourless in neutral and acidic solution. 

⭐When HCl is added to a solution of NaOH and phenolphthalein, its nature changes because of neutralisation and the resultant solution becomes neutral. Therefore the color of solution changes from pink to colorless.

Answer 2

Because HCL is an acid and Phenolphthalein is a acid/base indictor.

And Phenolphthalein changes its colour when reacted with an acid