Question

How do you calculate the pH of a strong acid or base?

Answer 1

You calculate it normally -> find the concentration of the acid, transfer the concentration and insert the value in a logarithmic equation.

Explanation:

To calculate pH in general, you need the concentration of hydrogen ions in the compound.

Strong acids are acids with a pH of less than 4-ish while weak acids have a pH of 4-ish to 7.0.

In order to find mols, we typically use stoichiometry and the concentration formula `(n=cv)`.

When you find concentration of an acid, you need to transfer the concentration to each individual element.

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E.g.

`H_"2"SO_"4" (aq) -> 2H^+ (aq) + SO_"4"^(2-) (aq)`

`H_"2"SO_"4"` has a concentration of `0.25` mol/L. You transfer the concentration just like how you would transfer mols in stoichiometry. THIS IS THE ONLY TIME YOU CAN TRANSFER CONCENTRATION

As a result, your hydrogen concentration is `0.5` mol/L.

Use the logarithm function to find pH:

`pH = -log [H^+]`

`=-log[0.5]`

`=0.301029995`

`=0.3`

In this example, the pH of `H_"2"SO_"4"` is `0.3`. This is a very small value, indicating its strong acidity.

Hope this helps :)