Question

Calculate the [H3O+] value of each aqueous solution.milk of magnesia with [OH−]=1.6×10−5M .

Answer 1

Step 1

The equations used here:

`\begin{gathered} pH\text{ = -log }\lbrack H3O+\rbrack\text{ \lparen1\rparen} \\ pOH\text{ = - log }\lbrack OH-\rbrack\text{ \lparen2\rparen} \\ pH\text{ + pOH = 14 \lparen3\rparen} \\ \end{gathered}`

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Step 2

Information provided:

[OH−] = 1.6×10^−5 M (It is the concentration of OH-)

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Step 3

Firstly, we begin with pOH as follows:

pOH = - log [OH−]

pOH = - log (1.6×10^−5 M) = 4.8

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Secondly, it is needed the equation (3) for pH:

pH + pOH = 14

pH = 14 - 4.8 = 9.2

pH = 9.2

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Thirdly, From (2), the concentration of H3O+ is found as follows:

pH = - log [H3O+]

It is needed the [H3O+], so it proceeds as follows:

[H3O+] = 10^-pH

[H3O+] = 10^-(9.2) = 6.3x10^-10 M

Answer: [H3O+] = 6.3x10^-10 M