Question

1. You are asked to prepare a buffered solution at a pH of 4.30 using the following acids and its potassium salt. What ratio of [HA] / [A- ] is required for each system?

a) Benzoic acid (C7H6O2, Ka = 6.4 x 10-5)

b) Hypochlorous acid (HClO; Ka = 3.5 x 10-8)

c) Which system would you choose to prepare the most effective buffering system? Explain.

d) For the system you chose, what mass (in grams) of all the necessary components do you need to weigh out in order to make a 2.00-L buffered solution? Assume no significant volume changes by the addition of the solid components

Answer 1

Answer:- 1. Required pH = 4.30 a) Benzoic acid (CHER, HQ = 6.4x10-5) CH 7* 6°2 = 6745099 Acid. +40 (conjugate base) (Salt) (PH) Buffer = pka + log Base Acid 4.3 Acid - log (ka) +10g (Base -103(6.4810-8) +1030 → 4.3 Base = Acid = 4.3 4.134 + log Base Acid = log Base] Acid = t o. 10618 Base o. 1618 lo = Acid -1.977 Ratio of Acid 1 O. 78308 Baše 1.277 b) Hypochlayous acid (HClO ; K= 3.5x108) Helo Acid - Holo + H I conjugate Ka = 3.5x10-8 Ka PH (k Hela) = -logta = 4.3 = pka +log Base 7.456. Lacid Base a 108 Acid = 4.3-7.456 = -3.156. Conte

Base LAcid -3.196 To = 0.000 698 Acid Base 1 0.000698 = 11432.66 C) I Would choose Benzoic acid and potassium salt of it, Can Ovey hypocholoyus acid because it's pka is closer to pH. A buffer Yesist pH only equal to pka 1. pH for Benzoic acid = 4.30 is in the range of pka, This is why it can maintain its pH upon adelition of +1. little bit of acid OY little bit of base. Benzoic acid is the most effective buffering System.

-0.783, If we -1.566 mol x 192.12 mol =191.248 4 (Benzoic acid Benzoate [Benzoic acid] 20.783 (Benpate] tave Molay Benzoate (Benzoic acid] -0.783M [Benzoate]1M Volume = glitre (Mole) Benzoic acid - Molarity x volume -1.566 mol (Molel Benzoate (potassium Benzoate = imel x 21 = 2 mol. Mass of Benzoic acid (Molel x Molay mass Mass of Potassium benzoate (Mole) x Molay mass - gmol x 160.12 g mol 0.783 med 320.248