Use the information in the following two tables to select suitable buffers for (

Question

Use the information in the following two tables to select suitable buffers for (a) pH=2.2 (b) pH=7.0 Table 8.1 Acidity and basicity constants at 198 15 K Table 8.2 Successive acidity constants of polyprotic acids at 298.15 K Acid 710 Carbonic acid, HCO Hydrosulfuric acid, H.S Oxalic acid, (COOH Phosphoric acid, H3PO4 4.3 x 10 13 688 5.9x 10-223 65x 10-5 76 x 10-3 1.0x10-2 2.00 5.6× 10-11 7.1 x 10-15 1.3×10. 12 x10 84 x 10 62 x 10- 2.6× 10-7 12 x 10-2 21 2.1 x10-3 67 29x 10 Sulfuric acid, H.SO Sulfurous acid, H2SO3 Beic ackd C.COOH 1.5x 102 Acetic acid CHCOOH Hypochieous acid HOO Boric aod, BCH x 10 60x103225x 10- 6x10- 2.3 x 10- Tartaric acid, C,HO, COOH) 56 x 10 9x10 2310 310 8x 10 1 x 10 1010 16x 10 1.7×10-8 8 x 10 23x 10 1 x 10 3 x10 65x 10

Explanation / Answer

use

pH = pKa + log(a-/HA)

we try to aim for A- = HA approx, so maximize the buffer cpaacity

so

pH = pKa

a)

pH = 2.2

get pKa = 2.2 near to this

best option will be phosphoric acid, H3PO4, and NaH2PO4

pKa = 2.12

B)

pH = 7

pKa = 7 approx

choose Hypochlorous acid, HClO, since pKa = 7.5

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