Compare the buffer capacity of 1 liter of regular buffer E to 1 liter of diluted buffer E in its ability to neutralize the addition of HNO3. Why is this so?

Question

I am confused on why the buffer capacity of a diluted buffer is less than that of a regular buffer. The buffer capacity of 1-L buffer in solution of 0.2 M HNO3 is .0419 and for a diluted buffer the capacity is .0256.

Answer 1

Buffer capacity can be defined as the moles of acid or base needed to change the pH of 1 liter of buffer by 1 pH unit.

In the example given in this problem, apparently buffer E is a basic buffer (such as NH₃/NH₄⁺). The reaction is the same in the original buffer as in the diluted buffer, and that is that the added H⁺ from HNO₃ reacts with the base to reduce the concentration of weak base and increase the concentration of the conjugate acid. This can be written as...

B + H⁺ ==> BH⁺

wk base.....acid...........conjugate acid

So the more moles of B that you have, the better it can react with H+. So, the original buffer will have more moles /liter than the diluted buffer. This explains why the buffer capacity is greater in the original.

Hope this makes sense.