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You prepare a buffer solution from 10.0 mL of 0.100 M MOPS (3-morpholinopropane-1-sulfonic acid) and 10.0...

You prepare a buffer solution from 10.0 mL of 0.100 M MOPS (3-morpholinopropane-1-sulfonic acid) and 10.0 mL of 0.079 M NaOH. Next, you add 1.00 mL of 1.65 × 10-5 M lidocaine to this mixture Denoting lidocaine as L, calculate the fraction of lidocaine present in the form LH .

ka=6.3e-8

kb=8.7e-7

Solutions

Expert Solution

millimoles of MOPS = 10 x 0.1 = 1

millimoles of NaOH = 10 x 0.079 = 0.79

Ka = 6.3 x 10^-8

pKa = -log Ka = 7.20

MOPS   +    NaOH     ------------> MOPS salt + H2O

   1            0.79                                 0                 0

0.21            0                                 0.79

pH = pKa + log [salt / acid]

    = 7.20 + log [0.79 / 0.21]

pH = 7.78

lidocaine Kb = 8.7 x 10^-7

Ka = Kw / Kb = 10^-14 / 8.7 x 10^-7 = 1.15 x 10^-8

[H+ ] = 10^-7.78 = 1.66 x 10^-8 M

fraction of lidocaine = [H+] / [H+] + Ka

                               = 1.66 x 10^-8 / 1.66 x 10^-8 + 1.15 x 10^-8

fraction of lidocaine = 0.591

queen_honey_blossom answered 2 years ago
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