Question

A sample of household ammonia has a pH of 11.50. What is the hydronium ion concentration of this solution?

Answer 1

Not high...

Explanation:

Water undergoes a measurable equilibrium....for which under standard conditions we write...

`2H_2O(l) rightleftharpoonsH_3O^+ + HO^-`

And `K_w=[H_3O^+][HO^-]`...and if take `log_10` of both sides...

`underbrace(log_10K_w)_(-pK_w)=log_10[H_3O^+]+log_10[HO^-]=log_(10)underbrace(10^-14)_(K_w)`

And on rearrangement...

`=-14=log_10[H_3O^+]+log_10[HO^-]`

Or....

`=+14=underbrace(-log_10[H_3O^+])_"pH"underbrace(-log_10[HO^-])_"pOH"`

And `pH+pOH=14` for water under standard conditions...

Confused yet? I include this bumf for background...

Anyway, finally to your question....we are given `pH=11.5`, i.e. we gots a basic solution...and so ...........

`[H_3O^+]=10^(-11.5)=3.16xx10^-12*mol*L^-1`...