Taking into account the definition of pH and pOH, the concentration of an aqueous solution of NaOH is 3.16×10⁻³ M.
pH is a measure of acidity or alkalinity that indicates the amount of hydrogen ions present in a solution or substance, which is defined as the negative base 10 logarithm of the activity of hydrogen ions, that is, the concentration of hydrogen ions or H₃O⁺:
pH= - log [H⁺]= - log [H₃O⁺]
Similarly, pOH is a measure of hydroxyl ions in a solution and is expressed as the logarithm of the concentration of OH⁻ ions, with the sign changed:
pOH= - log [OH⁻]
So, the following relationship can be established between pH and pOH:
pOH + pH= 14
You know that, in this case, an aqueous solution of NaOH that has a pH of 11.50. Then, pOH is calculated as:
pOH + 11.50= 14
Solving:
pOH= 14- 11.50
pOH= 2.50
Replacing this value in the definition of pOH:
2.50= - log [OH⁻]
Solving:
[OH⁻]= 10⁻² ⁵⁰
[OH⁻]= 3.16×10⁻³ M
A Strong Base is that base that in an aqueous solution completely dissociates into the cation or OH-, the concentration of the base being equal to that of the cation and OH-. Then [NaOH]= [OH-].
Finally, the concentration of an aqueous solution of NaOH is 3.16×10⁻³ M.
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