What are the ways to prove an acidic solution that it is acic?

Question

Aqueous solution of X is an acidic solution. As a chemistry student, describe briefly how you are able to prove that X is an acidic solution. You're not allow to use litmus paper, pH meter or any indicators.

Answer 1

Add sodium carbonate, or sodium bicarbonate (baking soda).

If the solution is quite acidic you will have H2CO3 forming which will break into H2O and CO2. The latter is a gas so you will see bubbles forming.

Answer 2

taste it...simple!!