Question

At work, you need to make a solution with the correct final pH so a life-saving medicine can be administered to a patient safely. You are using a citric acid-sodium citrate buffer system, which has a pKa of 6.40. If the prepared buffer has a citric acid concentration of 0.45M and a pH of 5.5, what concentration of sodium citrate do you need? 4 pts

Answer 1

To determine the concentration of sodium citrate needed in the citric acid-sodium citrate buffer system, you can use the Henderson-Hasselbalch equation:

pH = pKa + log10([A-]/[HA])

In this case, citric acid (HA) acts as the acidic component, while sodium citrate (A-) acts as the basic component. Given that the pKa of the buffer system is 6.4 and the pH of the prepared buffer is 5.5, we can set up the equation:

5.5 = 6.4 + log10([A-]/[HA])

Rearranging the equation, we have:

log10([A-]/[HA]) = 5.5 - 6.4
log10([A-]/[HA]) = -0.9

Taking the antilog of both sides, we get:

[A-]/[HA] = 10^(-0.9)

Simplifying, we have:

[A-]/[HA] = 0.126

Since the concentration of citric acid ([HA]) is given as 0.45 M, we can substitute this value into the equation:

0.126 = [A-]/0.45

Rearranging and solving for [A-], we get:

[A-] = 0.126 * 0.45
[A-] ≈ 0.0567 M

Therefore, you would need a concentration of sodium citrate (A-) of approximately 0.0567 M in order to achieve the desired pH of 5.5 in the citric acid-sodium citrate buffer system.