pH

[jkn1121]

• An enzymatic reaction takes place in 10 mL of a solution that has a total citrate concentration of 120 mM and an initial pH of 7.00. During the reaction 0.2 millimoles of acid are produced.

a) Using the data in the table below, calculate the final pH of the solution.

 

B) What would be the final pH in the absence of the citrate buffer? Assume that the other components of the solution have no significant buffering capacity and that the solution is initially at pH 7.00.

 

c) What would be the final pH if the solution contained 120 mM of phosphate buffer instead of citrate buffer?

 

 

 

Acid

 

Ka (M)

 

pKa

 

___________________________________

Citric Acid

 

7.41 x 10^-4

 

3.13 (pK1)

 

Citrate^-

 

1.74 x 10^-5

 

4.76 (pK2)

 

Citrate^2-

 

3.98 x 10^-6

 

5.40 (pK3)

 

H₃PO₄

 

7.08 x 10^-2

 

2.15 (pK1)

 

H₂PO₄^-

 

1.51 x 10^-7

 

6.82 (pK2)

 

HPO₄^2-

 

4.17 x 10^-13

 

12.38 (pK3)

 

I think using the pH= pka+ log (base/acid) I first take 10m x 120mM= 1200moles, then using 1/2(pka1+pka2) to determine which pka to use ill use pk1 and pk2 and then i get 3.945. Subtract then plug 1200mol for base, 3.945 for pka, and base as .2mM. final ph 7.72?

Edited August 31, 2010 by jkn1121