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

1 Answer
Ryuu
Feb 16, 2017

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.

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 :)

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