Question

1. A student performed the titration as in this experiment. He transferred a 2.00 mL sample of the acid into a flask, diluted it with water, and then began to add sodium hydroxide solution from the buret. After adding 50 mL of NaOH solution, the sample in the flask still had not turned pink. What error did the student make?

Answer 1

He did not add indicator. Without indicator we can not judge whether end point reached or not. Indicator is essential in titration as-

A substance that changes color in response to a chemical change is known as indicator. As an acid -base indicator (e.g. phenolphthalein) changes colour depending on pH.

The colour of indicator alters when the acidity or the oxidizing strength of solution reaches a critical range of values.

Phenolphthalein is a weak acid used as indicator in acid -base titration it's pH range is 8.3 and 10.0 the acidic solution is initially clear (colourless) but when base is added the solution turns pink momentarily but disappears with swirling the first permanent pink indicates end point.