Question

A buffer solution that is 0.100 M in both HCOOH and HCOOK has a pH = 3.75. A student says that if a very small amount of 0.100 M HCl is added to the buffer, the pH will decrease by a very small amount. Which of the following best supports the student's claim? (A) HCOO will accept a proton from HCl to produce more HCOOH and H2O(B) HCOOH will accept a proton from HCl to produce more HCOO and H2O. (C) HCOO wil donate a proton to HCl to produce more HCOOH and H2O (D) HCOOH will donate a proton to HCl to produce more HCOO and H2O.

Answer 1

Answer: Option (A) is the correct answer.

Explanation:

Chemical equation for the given reaction is as follows.

      $HCOO^{-}(aq) + H^{+}(aq) \rightarrow HCOOH(aq)$

And, the expression to calculate pH of this reaction is as follows.

      pH = $pk_{a} + log \frac{[HCOO^{-}]}{[HCOOH]}$

As the concentration of $HCOO^{-}$ is directly proportional to pH. Hence, when there occurs a decrease in the pH of the solution the $[HCOO^{-}]$ will also decrease.

Thus, we can conclude that the statement, HCOO will accept a proton from HCl to produce more HCOOH and $H_{2}O$, best supports the student's claim.