Calculate the [H3O+] concentration (in M) in a 0.1 M aqueous solution of NH3

[sayeo87]

Homework Statement

Calculate the [H3O+] concentration (in M) in a 0.1 M aqueous solution of NH3.
[Kb = 1.8 x 10–5 ]
(a) 7.5 x 10–12 M (c) 1.8 x 10–6 M
(b) 3.0 x 10–10 M (d) 1.3 x 10–3 M

Homework Equations

ΔTb = Kb x m

The Attempt at a Solution

So... I'm kind of at a loss here. First of all to do anything useful with the ΔTb = Kb x m equation, they would have to give ΔTb right? And also, because its an aqueous solution, I assume we are dissolving NH3 into water. The Kb of water is 0.512... why then do they give a Kb value of 1.8 x 10–5?

Thanks in advance The answer is a, btw, but why!?

 

[Borek]

They give Kb of ammonia. This is not an ebullioscopic constant, this is a dissociation constant.

calculation of pH of a weak acid/base

Or google for ICE table.


& pH calculator