Question

Calculate the pOH of the following solutions [OH-] = 4.3 x 10-6 M[OH-] = 2.0 x 10-6 M[OH-] = 4.5 x 10-11

Answer 1

Step 1 - Understanding the definition of pOH

pOH is defined as:

`pOH=-log[OH^-\rbrack`

I.e., we can calculate the pOH by knowing the concentration of OH- in the solution.

Step 2 - Calculating the pOH of the given solutions

a) The first solution has a OH- concentration of 4.3 x 10-6 M. We just need to set this value in the definition of pOH:

`\begin{gathered} pOH=-log4.3*10^(-6)=-[log4.3+(-6)log10\rbrack \\ \\ pOH=-log4.3+6=6-0.63=5.37 \end{gathered}`

b) The second solution has a OH- concentration of 2.0 x 10-6 M. Let's calculate its pOH:

`\begin{gathered} pOH=-log2*10^(-6)=-[log2+(-6)log10\rbrack \\ pOH=-log2+6=6-0.3=5.69 \end{gathered}`

c) The third solution has a OH- concentration of 4.5 x 10-11 M. Let's calculate its pOH:

`\begin{gathered} pOH=-log4.5*10^(-11)=-[log4.5+(-11)log10\rbrack \\ pOH=-log4.5+11=11-0.65=10.35 \end{gathered}`

Answer: the pOH of the solutions are, respectively, 5.37, 5.69 and 10.35