What fraction of ethane-1,2-dithiol is in each form (H2A, HA-, A2-) at pH=9.25? Please do show...

What fraction of ethane-1,2-dithiol is in each form (H2A, HA-, A2-) at pH=9.25? Please do show all work. Thank you!

Solutions

Expert Solution

ethane-1,2-dithiol pKa values

pKa1 = 8.43

pKa2 = 9.32

pH = pKa1 + log [HA-] /[H2A]

9.25 = 8.43 + log[HA-] /[H2A]

log [HA-] /[H2A]= 0.82

[HA-] /[H2A] = 6.61

fraction of [HA-] = [HA-] / ([H2A] + [HA-])

= [H-A] / ([HA-] + [HA-]/ 6.61)

=1 / 1 + 1/6.61

= 0.869

fraction of [HA-] = 0.869

fraction of [H2A] = 0.131

pH = pKa1 + log [A2-] /[HA-]

9.25 = 9.32 + log[A2-] /[HA-]

-0.07 = log[A2-] /[HA-]

[A2-] /[HA-] = 0.851

[A-2] = 0.851 x 0.869 =0.734

fraction of A-2 = 0.740

queen_honey_blossom answered 1 year ago

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