The total protonated from of EDTA is H 6 Y 2+ . Based on the pK values, calculat
ID: 901224 • Letter: T
Question
The total protonated from of EDTA is H6Y2+.
Based on the pK values, calculate the pH when the following form of EDTA exists dominantly in a 0.100 M aqueous solution.
(a) the H6Y2+ form of EDTA. (Hint: treat it as the monoprotic weak acid using the K1 as Ka to calculate H+ concentration for pH.)
(b) the zwitterion form (H4Y) of EDTA.
(c) the Na2H2Y form (H2Y2-) of EDTA.
(d) the Y4- form of EDTA. (Hint: treat it as the monobasic weak base using the Kb = Kw /K6 to calculate the OH- concentration, then get the pH from it.)
Explanation / Answer
a)
pH = pKa + log C
pH = 0.0 + log (0.1)
pH = -1
[H+] = 10 M
b)
pH = pKa + log C
pH = 6.16 + log (0.1)
pH = 5.16
c)
pH = pKa + log C
pH = 1.5 + log(0.1)
pH = 0.5
d)
pOH = pKb + log C
pOH = -log(10^-14/10^-10.24) + log (0.1)
pOH = 3.76 - 1
pOH = 2.76
pH = 14 - 2.76
pH = 11.24
pH = 14 - 0.3672
pH = 13.6328
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