mod/ibis/view.php?id-3746229 ESPN e] Yahoo! I ERYBES Run 2. play it now at Coo 6

Question

mod/ibis/view.php?id-3746229 ESPN e] Yahoo! I ERYBES Run 2. play it now at Coo 6/29/2017 1155 PM 15.4/100 Run 2-Playit now at Coo Apple Disney Print Calculator Periodic Table uestion 3 of 13 Map Sapling Learning The Kg values for several weak acids are given below. Which acid (and its conjugate base) would be the best buffer at pH 4.7? O O Tris: K-63-104 Acetic acid; Ka 1.8 x10 Formic acid: K. 1.8 x10 MES, K.-7.9 × 10" O HEPES, K,- 3.2 10 Abbreviations MES, 4-Morpholineethanesulfonic acid HEPES 4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid Tris: 2-Amino-2-hydroxymethyl-propane-1,3-diol

Explanation / Answer

for best buffer,

pH should be closer to pKa

so, the one whose pKa is closest to 4.7 is best for this case

so,

pKa = 4.7

use:

pKa = -log Ka

4.7 = -log Ka

Ka = 2.0*10^-5

The closest to this is Acetic acid whose Ka is 1.8*10^-5

Answer: Acetic acid: Ka = 1.8*10^-5

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