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# A-level chemistry buffers help! watch

1. Calculate the pH of a buffer solution which contains the weak monoprotic acid, propanoic acid (CH3CH2COOH), in concentration 0.1 moldm-3 and sodium propanoate in concentration 0.05 moldm-3. Ka of propanoic acid is 1.26×10-5 moldm-3.

Calculate the pH of the solution after 0.01 moles of NaOH are added to 500cm3 of the solution

Calculate the pH of the solution after 0.01 moles of HCl are added to 500cm3 of the solution.

I can do the first part but i dont under stand how to do the second two calculates without the volume of the solution being added, can anyone help?!
2. The volume of this buffer doesn't affect the pH (unless you seriously dilute it), since [HA] and [A-] will be affected by the same amount.

You can just use n(HA) and n(A-) in place of concs.

When you add some acid, the n(HA) increases by the n(H+) added and the n(A-) decreases by that amount.

Vice versa for adding OH-.

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