I have a titration question dealing with biochemistry

[Workout]

Homework Statement

You are titrating a 75 mL volume of 33 mM lactate buffer (pKa 3.86) with 1.3 M HCl (starting fully deprotonated). What is the pH after you have added 1 mL of the HCl? Give 2 decimal places

Homework Equations

pH = pKa + log[A-/HA]

The Attempt at a Solution

I don't really understand the concept of deprotonated and fully protonated. Could someone explain the two? I also have no idea where to even start with this question...

 

[AGNuke]

Deprotonated buffer - No H+ ions present in the buffer solution, meaning the buffer can no longer digest the base.

Protonation - Addition of H+.

If you add H+ in the buffer, you are protonating it, thus you are decreasing the pH of the buffer. If you want to attempt the question, ask yourself the following questions:-

1. How many moles of buffer I've been given? How much moles of H+ I am adding?

2. How much H+ can 1 mole of lactate buffer can assimilate?

3. Can I use the relevant equation?

 

[Borek]

You are not "protonating a buffer". You are protonating the conjugate base. So if there is only acid from (HLactate) in the solution, lactate is fully protonated. That will happen at low pH. If there is a mixture of HLactate and Lactate^- - it is protonated only partially, that happens when the pH is relatively close to pK_a. Finally, in high pH all lactate is present in Lactate^- form and it is not protonated at all.

You can assume protonation is quantitative - all strong acid added reacts with Lactate^- yielding HLactate. Use this information to calculate new concentrations of acid and conjugate form and plug them into the Henderson-Hasselbalch equation.

Also compare this buffer pH change problem.