If 50 mL of 0.2 M NaC2H3O2 and 10 mL of 1.0 M HC2H3O2 are diluted to a final volume of 100 mL, what is the pH of the buffer solution?

Most of these look like dilution questions which follow a general pattern;

Use M1V1 = M2V2 (because moles in a solution stays constant if diluted)

so, the Concentration before * Volume before = Concentration after * Volume after

Using the first question as an example; 0.2*50 = 100 * M2

Rearranging for M2: 0.1

Therefore the concentration of the final solution is 0.1 M

we know that to work out pH you must use negative logs to base 10; i. e. - log (0.1) gives you the pH for this solution which is 1