What is the final ph of a solution created by adding 12 ml of 0.5 m hcl to 300 ml of 100 mm formate if the pka for formic acid is 3.78?

First, calculate the number of moles for the salt and the acid:

Mole of salt formate:

I think the concentration is 1.00 M or moles per liter. A concentration of 100 M is not logical.

(1 mol/L) * (1L/1000mL) * (300 mL) = 3 moles formate

Moles of acid:

(0.5 mol/L) * (1L/1000 mL) * (12 mL) = 0.06 moles HCl

Then, we use the modified Henderson-Hasselbach equation:

pH = pKa + log[salt/acid]

pH = 3.78 + log (3/0.06)

pH = 5.48