When a person exercises, muscle contractions produce lactic acid. Moderate incre

Question

When a person exercises, muscle contractions produce lactic acid. Moderate increases in lactic acid can be handled by the blood buffers without decreasing the pH of blood. However, excessive amounts of lactic acid can overload the blood buffer system resulting in the lowering of the blood pH. A condition called acidosis is diagnosed if the blood pH falls to 7.35 or lower. Assume the primary blood buffer system is the carbonate buffer system shown below. Calculate what happens to the [H_2CO_3]/[HCO_3^-], ratio when the pH decreases from 7.40 to 7.35. H_2CO_3a (aq) HCO_3^- (aq) + H^+(aq) k_a1 = 4.3 times 10^-7

Explanation / Answer

Using Henderson Hasselbach equation:

pH = pKa + log([HCO3-]/[H2CO3])

At pH = 7.4:

7.4 = 6.36 + log([HCO3-]/[H2CO3])

So,

([HCO3-]/[H2CO3]) = 107.4-6.36 = 10.96

So,

([H2CO3]/[HCO3-]) = 0.0912

At pH = 7.35:

7.35 = 6.36 + log([HCO3-]/[H2CO3])

So,

([HCO3-]/[H2CO3]) = 107.35-6.36 = 9.77

So,

([H2CO3]/[HCO3-]) = 0.102

So the ratio ([H2CO3]/[HCO3-]) increases from 0.0912 to 0.102

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