Question

Part A

At a pH of 7.40, what is the ratio of the molar concentrations of PO43− to HPO42−? Express your answer using two significant figures.

Part B

At a pH of 7.40, what is the ratio of the molar concentrations of PO43− to HPO42−?

Express your answer using two significant figures.

Part C

At a pH of 7.40, what is the ratio of the molar concentrations of H2PO4− to H3PO4?

Express your answer using two significant figures.

Part D

At a pH of 7.40, what is the ratio of the molar concentrations of CO32− to HCO3−?

Express your answer using two significant figures.

Part E

At a pH of 7.40, what is the ratio of the molar concentrations of HCO3− to H2CO3?

Express your answer using two significant figures.

Part F

Normal metabolic processes produce significant amounts of acid, sometimes up to 10 mol/day, in the human body. Thus it is desirable that the buffer system for blood contain more conjugate base than acid.

Which conjugate acid-base pair is most responsible for maintaining the pH of blood?

[HPO42−]/[H2PO4−]

[H2PO4−]/[H3PO4]

[HCO3−]/[H2CO3]

[CO32−]/[HCO3−]

[PO43−]/[HPO42−]

Answer 1

To calculate the relations of conjugate pairs of acid / base, the Henderson-Hasselbach equation is used:

pH = pKa + Log [Base] / [Acid]

It is cleared of the form:

[Base] / [Acid] = 10 ^ pH-pKa

and it is calculated:

A) [PO4-3] / [HPO4-2] = 10 ^ (7.4-12.32) = 1.20x10 ^ -5

B) [PO4-3] / [HPO4-2] = 10 ^ (7.4-12.32) = 1.2x10 ^ -5

C) [H2PO4 -] / [H3PO4] = 10 ^ (7.4-2.12) = 1.9x10 ^ 5

D) [CO3-2] / [HCO3-] = 10 ^ (7.4-10.32) = 1.2x10 ^ -3

E) [HCO3 -] / [H2CO3] = 10 ^ (7.4-6.37) = 1.1x10 ^ 1

F) The buffer that maintains the pH of the most important blood is the one formed by: [HCO3 -] / [H2CO3].