Question

A buffer can be made from Citric Acid and Sodium Citrate Monobasic. What molar ratio of Sodium Citrate Monobasic to Citric Acid would be used to create a buffer with a pH of 2.14? Citric Acid pKa=3.14 Enter your answer as a whole number ratio Example: 7:1

I did the equation and got 0.1 but I don't know how to write the answer as a ratio.

Answer 1

Henderson Hasselbalch equation:

pH = pKa + log([Salt]/[Acid])

or
pH = pKa + log([Sodium Citrate Monobasic]/[Citric acid])

Given: pH is 2.14, pKa is 3.14

So, 2.14 = 3.14 + log([Sodium Citrate Monobasic]/[Citric acid])

=> log([Sodium Citrate Monobasic]/[Citric acid]) = 2.14 - 3.14

=> log([Sodium Citrate Monobasic]/[Citric acid]) = -1

=> [Sodium Citrate Monobasic]/[Citric acid] = 10^-1

=> [Sodium Citrate Monobasic]/[Citric acid] = 0.1

=> [Sodium Citrate Monobasic]/[Citric acid] = 1/10

So, molar ratio of [Sodium Citrate Monobasic] to [Citric acid] = 1 : 10

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