Question

Select the pH value you would expect for each of these solutions.


an aqueous solution of HNO3


an aqueous solution of NaCl


an aqueous solution of NaOH

Answer 1

You need the concentration to give exact numbers. In general:

- HNO3: acidic (pH < 7). For example, a 0.10 M HNO3 solution fully dissociates to give [H+] = 0.10 M, so pH = −log(0.10) = 1.00 (at 25 °C).
- NaCl: neutral (pH ≈ 7). Salt of a strong acid and a strong base; an aqueous NaCl solution is essentially neutral (small deviations can occur from dissolved CO2 or impurities).
- NaOH: basic (pH > 7). For example, a 0.10 M NaOH solution gives [OH−] = 0.10 M → pOH = 1 and pH = 14 − 1 = 13 (at 25 °C).

Formulae: pH = −log[H+]; pOH = −log[OH−]; pH + pOH ≈ 14 at 25 °C.