This is a chemistry question, I understand you need to use the Henderson-Hasselb

Question

This is a chemistry question, I understand you need to use the Henderson-Hasselbach equation and the answer is 9% unprotonated by (.1/1.1) and I'm wondering how to get the divided total of 1.1. The question is: Since the patient was brought into the emergency room only two hours after the overdose, you suspect that her stomach might contain undissolved aspirin that is continuing to be absorbed. The fact that she is experiencing severe respiratory alkalosis 10 hours after the ingestion confirms your suspicion and you decide to use a gastric lavage at pH 8.5 to effectively remove any aspirin that still remains in the stomach. Calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH of the stomach, which is usually around 2.0.

Explanation / Answer

t = 10 after

pH = 8.5

For aspirin --> pKa = 3.50

so

the hendesron equation:

pH = pKa + log(A-/HA)

2 = 3.5 + log(a-/HA)

A/HA = 10^(2-3.5) = 0.0316227

molecules of A- 0.0316227, molecules of HA

unprotonation = 0.0316227/(0.0316227+1) = 0.030650; to % --> 0.030650*100 = 3.06 % is unprotonated

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