Preparing a buffer: Which acid would you choose to combine with its sodium salt
ID: 944582 • Letter: P
Question
Preparing a buffer: Which acid would you choose to combine with its sodium salt to make a solution buffered at pH 7.35? For the best choice, calculate the ratio of the conjugate base to the acid rccquired to attain the desired pH. Chlorous Acid (HCIO2) pKa = 1.95 Nitrous Acid (HNO2) pKa = 3.34 Formic Acid (HCHO2) pKa = 3.74 Hypochlorous Acid (HCIO) pKa = 7.54 6. Strong acid-strong base titration pH curve: Calculate the pH in the titration in example 6 after the addition of 60.0 mL of 0.200 M HNO3. 7. Weak acid - strong base titration curve: Determine the pH of at the equivalence point for the titration of HNO2 and KOH in example 7.Explanation / Answer
The curve for question 6 and 7 are not there, and the example either. But I can answer to you the question 5.
The best one to get a pH of 7.35 would be the one where it's pKa value is really close to the pH you want. In this case, the last would be the best and the ratio of their concentration is:
7.35 = 7.54 + log (ClO-/HClO)
-0.19 = log (ClO-/HClO)
10-0.19 = (ClO-/HClO)
(ClO-/HClO) = 0.65
If you do the same thing with the other acid, the relationship would be way too high. So this is the best option.
Hope this helps.