Question

1. a)Which of the following statements are TRUE for a buffer solution.
Select all that are True.
_ A buffer can be prepared by combining a weak acid and its conjugate base."
_ A buffer resists changes in pH.
_ When a strong acid is added to a buffer, it reacts with the conjugate base which slightly increases the pH of the solution.

3. Given the following data set: Indicate where the buffere capacity has been exceeded.

Solution	pH	Change in pH
Acetic acid (25 mL)	2.88
Sodium acetate	7.46
Mixture (50 mL)	4.70
After 5 mL NaOH	4.90	0.20
After 10 mL NaOH	5.13	0.23
After 15 mL NaOH	5.42	0.29
After 20 mL NaOH	5.95	0.53
After 25 mL NaOH	11.17	5.22

The buffer capacity was exceeded when_______mL of NaOH was added?

Answer 1

1 Ans: All the statements are True

Explanation: A buffer solution is formed by a weak acid example Acetic acid and its conjugate base example Acetate.

Purpose of the buffer solution is to resist the change in pH when a strong acid or base is added to it.

When a strong acid is added it'll give H + ions which ions will cause increase in pH but at the same time the conjugate base example Acetate will combine with those free H + ions and itself form acetic acid ( now Hcl which is a strong acid is replaced by a weak acid Acetic acid so there would be only minor rise in pH instead of large.

2 Ans : Till after addition of 20ml of NaOH there is only slight rise in pH but after addition of 25 ml of NaOH the pH incresed by 5.22 so here the buffering capacity was exceeded , that is there was no more acetic acid left to neutralise the NaOH and therefore due to excess NaOH the pH suddenly increased to a higher value.

At this pH now the solution contains NaOH and less of buffer.

So The buffer capacity was exceeded when 25ml of NaOH was added