Given:

Concentration of acetic acid 0.1M and 30mL used.
Concentration of hydrocholoric acid 0.1M and 15mL used.
Concentration of sodium hydroxide 0.1M and 5mL used.

I need to calculate the pH before any NaOH is added and after the NaOH is added.

I think i am suppose to use the Henderson-Hasselbach equation but i don't know how.
The equation is pH= pKa + log[conjugate base]/[acid]

I understand that [conjugate base]/[acid] will be a 2/1 ratio so the log of that is 0.30. But i don't know how to get the pKa?

To calculate the pH before any sodium hydroxide (NaOH) is added, you need to find the pKa (the negative logarithm of the acid dissociation constant, Ka) value of acetic acid. The pKa is a measure of the acid's strength and determines the pH of the solution.

To find the pKa of acetic acid, you have two options:

1. Look up the pKa value in a reliable reference source, such as a chemistry textbook, handbook, or online database. The pKa of acetic acid is approximately 4.76.

2. If you don't have access to a reference source, you can calculate the pKa using experimental data. The equation for the dissociation of acetic acid is:

CH3COOH ⇌ CH3COO- + H+

To find the pKa, you need the equilibrium concentrations of acetic acid ([CH3COOH]) and its conjugate base ([CH3COO-]). In this case, the initial concentration of acetic acid is 0.1 M, and it dissociates into CH3COO- and H+ in a 1:1 ratio. Therefore, after dissociation, the concentration of CH3COO- will be 0.1 M, and the concentration of H+ will also be 0.1 M.

Using these concentrations, you can calculate the pH before NaOH is added using the Henderson-Hasselbalch equation:

pH = pKa + log([CH3COO-] / [CH3COOH])

Since the ratio [CH3COO-] / [CH3COOH] is 1, the logarithm of 1 is 0, so the pH before NaOH is added will be equal to the pKa. Therefore, in this case, the pH before NaOH is added will be approximately 4.76.

After calculating the pH before NaOH is added, you can perform similar calculations to determine the pH after NaOH is added using the Henderson-Hasselbalch equation with the new concentrations of acetic acid and its conjugate base after the reaction between NaOH and acetic acid takes place.