Question

A solution of ammonia has a pH of 11.8. What is the concentration of OH– ions in the solution?-1.58 x 10^–12 M-6.31 x 10^–3 M-2.20 M-158 M

Answer 1

INFORMATION:

We know that:

- A solution of ammonia has a pH of 11.8

And we must find the concentration of OH– ions in the solution

STEP BY STEP EXPLANATION:

To find it, we need to know that pH & pOH are related by the following equation

$pH+pOH=14$

Now, using the given information, we know that pH = 11.8

Then, replacing the value in the formula

$11.8+pOH=14$

Solving for pOH,

$\begin{gathered} pOH=14-11.8 \\ pOH=2.2 \end{gathered}$

The concentration of OH- ions is given by

$pOH=-log\lbrack OH^-\rbrack$

Replacing the value of pOH,

$2.2=-log\lbrack OH^-\rbrack$

Finally, solving for OH-

$\begin{gathered} -2.2=log\lbrack OH^-\rbrack \\ OH^-=10^{-2.2} \\ OH^-=6.31\times10^{-3} \end{gathered}$

Hence, concentration of OH- is 6.31 x 10^-3 M

ANSWER:

6.31 x 10^-3 M