Question

please answer number 5 and 6

5. The buffer range for a given weak acid/conjugate base pair is pK, 11. Explain why. 6. A weak triprotic acid, HZZ has the following K, values: Ki = 1.4 x 104 K = 9.7 x 10-7 K 5.3 x 109 a. Write the NIE associated with each Ka value. b. Of the four weak acid species: H.Z, H,Z, HZz"; which two could be used to prepare a buffer of pH = 3.55? Explain. c. A buffer is made by pouring 250.0 mL of 1.688 M Na, HZ into 350.0 mL of 1.455 M Z Cit. Calculate the pH of this buffer solution. d. Calculate the pH if the original buffer solution is diluted to 1200 mLs.

Answer 1

Solution:

A buffer solution resists the significant change in pH when a strong acid or base is added. The buffering capacity of an acidic buffer lying between pka +1 and pka -1. Beyond these values the buffering capacity of a buffer is considerd to be destroyed.

The pH of a buffer is calculated as,.

pH = pka + log [Conjugate base / Acid]

Hence,

For pH = pka +1

The concentration of conjugate base must be ten times of acid.

For pH = pka -1

The concentration of acid must be ten times of conjugate base.