Question

What is the pH of a 0.0538 M solution of Sr(OH)2?

How do you know when you have to multiply the M before finding the pH?

Answer 1

Step 1

Sr(OH)2 is a strong base. It means that it is completely dissociated in an aqueous solution.

Sr(OH)2 => Sr+2 + 2OH-

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Step 2

pH is asked here, but there is a base, so let's calculate pOH first.

$\begin{gathered} pOH\text{ = -log}\lbrack OH-\rbrack \\ Attention:\text{ OH- Concentration here is twice} \\ \end{gathered}$

Sr(OH)2 => Sr+2 + 2OH-

0.0538 M 0.0538 M 2 x 0.0538 M

Therefore, pOH = -log (2x0.0538M) = 0.97 approx.

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Step 3

Now, pH + pOH = 14 => pH = 14 - pOH = 14 - 0.97 = 13.03

Answer: pH = 13.03