Question

The pH of a solution is 8.7, what is the pOH?

Answer 1

pOH = 5.3

Explanation:

You can answer this question in one of two ways:

• Take the anti-log of the pH to obtain the concentration of `H^+` ions in solution. After that, use the self-ionization of water formula:
  

Where `K_w` has a value of `1.0xx10^-14` Then you can rearrange the equation to solve for [`OH^-`]. Take the -log of that value to obtain the pOH.

• Subtract the pH from 14 to obtain the pOH.

I'll show you both ways using these equations:

THE PROCESS FOR METHOD 1:

`[H^+]= 10^(-8.7) = 1.995xx10^-9 M`
`K_w = ["H"_3"O"^(+)]["OH"^(-)] = 1.0xx10^(-14)`

Kw / [H+] = [OH-]

`(1.0xx10^(-14))/(1.995xx10^(-9) "M") = 5.01xx10^(-6)"`
`[OH^(-)] = 5.01xx10^(-6)M`
`pOH = -log(5.01xx10^(-6))M`
`pOH = 5.3`

THE PROCESS FOR METHOD 2:

`14-8.7 = 5.3`