Chemistry

Chemistry

Problem

The pH of blood stream is maintained by a proper balance of H2CO3\text{H}_2\text{CO}_3 and NaHCO3\text{NaHCO}_3 concentrations. What volume of 5 M NaHCO3\text{NaHCO}_3 solution should be mixed with a 10 mL sample of blood which is 2 M in H2CO3\text{H}_2\text{CO}_3 in order to maintain a pH of 7.4? KaK_a for H2CO3\text{H}_2\text{CO}_3 in blood is 7.8×10−77.8 \times 10^{-7}.
Intuitive explanation

This is a buffer problem where you need to use the Henderson–Hasselbalch equation to find the right ratio of weak acid to conjugate base. The key insight is that pH depends on the ratio of NaHCO3\text{NaHCO}_3 (the conjugate base) to H2CO3\text{H}_2\text{CO}_3 (the weak acid), not their absolute amounts—so you can set up an equation using the given KaK_a and desired pH to solve for the volume needed.

Intuitive explanation

This is a buffer problem where you need to use the Henderson–Hasselbalch equation to find the right ratio of weak acid to conjugate base. The key insight is that pH depends on the ratio of NaHCO3\text{NaHCO}_3 (the conjugate base) to H2CO3\text{H}_2\text{CO}_3 (the weak acid), not their absolute amounts—so you can set up an equation using the given KaK_a and desired pH to solve for the volume needed.

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