Question

13. Calculate the [H3O+] for each of the following solutions: 0.0015 M HNO3, pH = 4.525, pOH = 12.28, [OH-] = 2.5 X 10-5, pH = 11.52

Answer 1

For HNO3 solution.

HNO3 is a strong acid and it dissociates fully, 100%.

HNO3 + H2O à H3O⁺ + NO3^-

So, the [H3O⁺] = 1.5x10^-3 M

For pH=4.525

by definition, pH = - log[H3O⁺] or log[H3O⁺]= -pH = -4.525

so, [H3O⁺] = 10^-4.525 =2.985x10^-5 M

For pOH = 12.28

We know pH=14-pOH =14-12.28=1.72

[H3O⁺] = 10^-1.72 = 1.90x10^-2 M

For [OH-] = 2.5x10^-5

pOH = -log[OH-] = - log2.5x10^-5 = -(-4.60) = 4.60

so, pH = 14-4.60 = 9.40

Therefore, [H3O⁺] = 10^-9.40 M = 3.98x10^-10 M

For pH=11.52

[H3O⁺] = 10^-11.52 = 3.01x10^-12 M