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

Answer 1

pOH = 5.3

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#

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Answer 2

Ellie Andrews

To find the pOH of a solution, subtract the pH from 14. pOH = 14 - pH pOH = 14 - 8.7 pOH ≈ 5.3

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.