Question

A buffer solution contains 0.20 moles of methanoic acid, HCOOH, and 0.30 moles of sodium methanoate, NaCOOH, in 1.00 L of the buffer. The Ka of HCOOH = 1.8 x 10-4.

a) Calculate the pH of this solution Using pH = pkA + log([CB]/[Acid]), I calculated the pH of this buffer is 3.88.

b) Describe how the capacity of this buffer to neutralize acid compares to the ability of this buffer to neutralize base.

I am wondering since there is a higher concentration of conjugate base than acid in the buffer solution, does this mean it is better able to neutralize added acid than base?

c) Describe how bubbling 0.10 mol of HCl gas through a liter of the buffer would affect the pH of the buffer solution.

I am wondering Is adding HCl gas the same as adding HCl solution to the buffer?

Thank you for your responses

Answer 1

The pH of the buffer containing methanoic acid and sodium methanoate is 3.88, and due to a higher concentration of conjugate base, the buffer has a greater capacity to neutralize acids over bases. Bubbling HCl gas through the buffer will work similarly to adding HCl solution, leading to a reaction with the conjugate base and slight pH change.

Step-by-step explanation:

Understanding Buffer Solutions and pH Changes

a) You have correctly calculated the pH of the buffer solution using the Henderson-Hasselbalch equation, resulting in a pH of 3.88 for the methanoic acid (HCOOH) and sodium methanoate (NaCOOH) buffer solution. This equation works because it relates the pH of a buffer to the pKa of the acid and the ratio of the concentrations of the conjugate base and the acid.

b) Since the buffer has a higher concentration of conjugate base than acid, it will indeed have a greater capacity to neutralize added acids compared to bases. This is because the added acid will react with the conjugate base present in greater proportion, forming more of the weak acid and thus resisting changes in pH.

c) Bubbling HCl gas through the buffer will have the same effect as adding HCl solution, assuming it dissolves completely and reacts with the buffer components. The HCl will react primarily with the sodium methanoate to form more methanoic acid and reduce some of the buffer's capacity to neutralize additional acid. However, the pH will still change less than if no buffer were present, which demonstrates the buffering action.