[Sis290025]

The internal pH of a muscle cell is 6.8. Phosphate in the muscle cell, 10 mM, can exist in 4 forms; the pKa’s are 2.15, 6.78, 12.4. At the pH of a muscle cell, how much of each form of phosphate [H3PO4, H2PO4 (-) , HPO4 (2-) and PO4 (3-)] is present? You need to calculate this for each form, some will be present at a very much higher concentration than others.

Before solving this, does the concentration 10 mM correspond to the PO4 (3-) concentration?

Thank you for any response.

[Borek]

10 mM is a sum of concentrations of all forms.

Look here for a hint:

http://www.chembuddy.com/?left=pH-calculation&right=pH-polyprotic-acid-base