Homework Answers
as a rule of thumb if you want buffer at given pH then select that acid whose pka lies such that pH = pka -1 to pKa +1
First we calculate pKa = -log Ka
(a) acetic acid = -log (1.8*10^-5) = 4.74
(b) Phosphoric acid = -log (7.1*10^-3) = 2.16
(c) Hypochlorous acid : -log (3.5*10^-8) = 7.53
1. For Buffer with pH = 2.8 pka should be 1.8 to 3.8 so phosphoric acid would be the ideal choice
H3PO4 + NaOH -----> NaH2PO4 (conjugate base) along with H3PO4
2. For Buffer with pH = 4.5 pka should be 3.5to 5.5 so acetic acid would be the ideal choice
CH3COOH+ NaOH -----> CH3COONa (conjugate base) along with CH3COOH
3. For Buffer with pH = 7.5 pka should be 6.5 to 8.5 so hypochlorous acid would be the ideal choice
HCLO+ NaOH -----> NaClO (conjugate base) along with HClO
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