   Chapter 15, Problem 46E

Chapter
Section
Textbook Problem

# 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 a 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 described in Exercise 45. Calculate what happens to the [H2CO3]/[HCO3−] ratio in blood when the pH decreases from 7.40 to 7.35.

Interpretation Introduction

Interpretation:

By taking the reference of exercise 45 , the ratio of [H2CO3]/[HCO3] is to be calculated when the pH decreases from 7.40 to 7.35 .

Concept introduction:

The pH value is the measure of H+ ions. The relation between pH and pKa is given by Henderson-Hassel Bach equation. According to this equation,

pH=pKa+log[Base][Acid]

To determine: The affect on the ratio, [H2CO3]/[HCO3] when the pH decreases from 7.40 to 7.35 .

Explanation

Explanation

To determine the ratio, [H2CO3]/[HCO3] at pH 7.40

The concentration of carbonic acid is 0.0012 .

The concentration of carbonate ion at pH 7.40 is 1.3×102M .

The ratio of [H2CO3]/[HCO3] at pH 7.40 is,

[H2CO3][HCO3]=0.0012M1.3×102M=0.092_

To determine the ratio, [H2CO3]/[HCO3] pH 7.35

Given

The concentration of carbonic acid is 0.0012 .

The value of pH is 7.35 .

The value of Ka for carbonic acid is 4.3×107 .

Formula

The pH is calculated using the Henderson-Hassel Bach equation,

pH=pKa+log[HCO3][H2CO3]

Where,

• pH is the measure of H+ ions.
• pKa is the measure of acidic strength.
• [HCO3] is concentration of bicarbonate (HCO3) .
• [H2CO3] is concentration of carbonic acid.

The formula of pKa is,

pKa=logKa

Where,

• Ka is acid equilibrium constant.

Substitute the value of pKa in Henderson-Hassel Bach equation.

pH=logKa+log[HCO3][H2CO3]

Substitute l the values of pH,[H2CO3] and Ka in the above equation

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