4. Under normal metabolic conditions, the concentration of hydrogen ions, [H+],

Question

4. Under normal metabolic conditions, the concentration of hydrogen ions, [H+], in blood is 4x10-8 M, a. What is the pH of human blood under normal metabolic conditions? Show your calculation. b. A major buffer system of human blood relies on carbonic acid (H2CO3) and its conjugate base bicarbonate (HCO3-). The pKa for carbonic acid is 4.77. Calculate the ratio of [HCO3-] to [H2CO3] in blood under normal metabolic conditions. Show your calculation. c. Based on your answer above, which exists at a higher concentration in blood: carbonic acid (H2CO3) or bicarbonate (HCO3-)? d. When we exercise vigorously, metabolism in our muscles releases a lot of carbon dioxide into our bloodstream. The carbon dioxide combines with water to form carbonic acid (shown below). Will this tend to raise or lower the pH of our blood? Explain your answer in a few words. (No calculation needed.

Explanation / Answer

a)

pH of human blood, nomally.. from databases:

pH should be around = 7.36 or simply 7.4

from calculation:

pH = -log([H+]) = -log(4*10^-8) =7.3979

b)

(acid) H2CO3 + HCO3- (conjguate base)

pKa = 4.77

find ratio from Henderson hasselbach equation:

pH = pKa + log(conjugate base/acid)

7.4 = 4.77 + log(ratio)

ratio = 10^(7.4 -4.77 ) = 426.5

[HCO3-] = 426.5*[H2CO3]

c)

as sshown before, there is much more HCO3- than H2CO3 in blood

d)

CO2 blood's water = H2O + CO2 = H2CO3

This will favour H2CO3, so this DECRASES the ratio

a decrease in ratio will lower the pH of blood

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