Lactic Acid: Ionised or Non-Ionised in Human Body?

[josephcollins]

Hi guys,
Could anyone give me a hand with this one?

During exercise, 2-hydroxypropanoic acid (lactic acid) is produced in the muscles. Deduce whether the ionised or non-ionised form of this weak acid (Ka=1.4*10^-4) is mainly present at the pH of the human body (pH=7.4).

 

[chem_tr]

Well, your teacher is a creative one

Let's assume that blood is a buffer substance with pH value of 7,4. So just find the pH value of lactic acid (or lactate) in pH 7,4 buffer. It seems that the acid form will dominate, but I may be wrong. You'll know this when you solve the H-H equation or the contribution of LA in blood.

 

[chem_tr]

Let's start from somewhere:

$$HLac \xrightarrow {ionization} H^+ + Lac^-$$

In here, a very small amount of HLac will be produced in a relatively vast amount of buffer; so it will probably be ionized. The initial concentration of lactic acid is low I think, and it also decreases due to low ionization. So we don't really need to know the initial concentration; it will surely be ionized, contrasting to my earlier thread.