Ion effect and buffers

Question

Kriel just discovered a new protein, Krielase and for it not to unfold and lose its function, he

realized that the protein needs to be constantly immersed in a pH = 6.50 solution. He is therefore interested in preparing a 50 mL 0.08 M pH = 4.50 buffer to contain the protein. He listed down the pure acids available to his disposal, and also looked for their acid dissociation constant (Ka) values.



Acid Name	Ka1	Ka2	Ka3
Nitrous Acid (HNO2)	4.00 x 10-4	N/A	N/A
Acetic Acid (CH3COOH)	1.76 x 10-5	N/A	N/A
Ascorbic Acid (HAsc)	7.90 x 10-5	1.60 x 10-12	N/A
Phosphoric Acid (H3PO4)	7.52 x 10-3	6.23 x 10-8	4.28 x 10-13

A. Identify which weak acid system is best to use in preparing the buffer? Why?

B. Identify the species which will make up the buffer system? Identify which one will

neutralize the acidic disturbance, and the one which will react with an added base.

C. Calculate the amount (in mmoles) of each of the components necessary to prepare

the buffer?

D. Indicate how Kriel is supposed to prepare the buffer from 6.0 M of the acid and 6.0 M

NaOH.

E. Calculate the resulting pH if 5 drps 0.5 M HCl was accidentally added to the buffer.

To validate the pH of the buffer solution he prepared, Kriel decided to do pH testing using a pH meter.

F. Assess the effect on the pH and buffer capacity of the buffer solution if the pH meter

used to measure it is still wet with water. Expound. Kriel then decided to continuously monitor the pH of the protein-buffer solution by incorporating few drops of colored indicator. Provided a list of visual indicator in the next page.

G. Identify which indicator is best to use in monitoring minimal but critical changes in

the solution pH.

pKa	HInd	Ind
Thymol Blue	1.50	red yellow
Bromocresol Green	4.70	yellow blue
Phenol Red	7.90	yellow red
Phenolpthalein	9.40	colorless pink

H. Identify the color of the buffered solution if drops of Phenol Red was added to it.

Answer 1

Hey, this is alot, but I'd love to help.

To get you started, for part A

if pH of desired buffer=x

use the weak acid which has a pka as close to x as possible