You are given an unknown solution that is one of the followi

You are given an unknown solution that is one of the following: 0.1M HCl, 0.1M H2SO4, or 0.1M H3PO4. Given only 0.1M NaOH, deionized water, phenolphthalein, and a few test tubes, describe how you would identify the unknown acid.

Solution

Take 10ml of each acid in 3 different test tubes and add 2-3 drops of phenolphthalien indicator and then add given NaOH.

If the acid is HCl its a monoprotic acid which reacts with NaOH at a ratio 1:1 I,e 10ml of acid gives end point permanent pale pink at the consumption of 10ml of base. This indicates its HCl acid.

If it is H2SO4 a diprotic acid reacts with NaOH at a ratio of 1:2 I,e 10ml of H2SO4 consumes 20ml of NaOH to give the end point, a permanent pale pink color.

If the acid is H3PO4, although the reaction occurs no end point color change is observed as seen in the above experiments. Because phenolphthalien indicator is not suitable for this reaction. Although often the H3PO4 is listed under strong mineral acids its relatively weak acid.

Note: Phenolphthalien indicator is suitable only for strong acid -strong base titrations.