What concentrations of acetic acid (pKa = 4.76) and acetate would be required to

Question

What concentrations of acetic acid (pKa = 4.76) and acetate would be required to prepare a 0.15 M buffer solution at pH 5.0? Rearrange the Henderson-Hasselbalch equation to solve for the ratio of base (acetate) to add (acetic acid), [A^-]/[HA] Use the mole fraction of acetate to calculate the concentration of acetate Calculate the concentration of acetic acid. That is, there are 1.7. That is there are 1.7 molecules of acetate for each molecule of acetic acid. Step 1: The ratio of base to add is 1.7. Step 2: The mole fraction of acetate is 0.63, and the concentration of acetate is 0.094. Step 3: Calculate the concentration of acetic acid.

Explanation / Answer

PH = 5

PKa = 4.76

[Acetate ion] = 0.15M

PH = Pka + log[Acetate ion]/[Acetic acid]

5 = 4.76 + log[Acetate ion]/[Acetic acid]

log[Acetate ion]/[Acetic acid] = 5-4.76

log[Acetate ion]/[Acetic acid]   = 0.24

[Acetae ion]/[Acetic acid]        = 100.24

[Acetate ion]/[Acetic acid]        =1.7378

[Acetate ion]              =     1.7378[Acetic acid]

total concentration of acetic acid and acetate ion = 0.15M

Acetic acid + acetate ion = 0.15M

Let concentration of acetic acid is x and concentration of acetate ion is 1.7378x

Acetic acid + acetate ion = 0.15M

x + 1.7378x   = 0.15

x =0.0547M

concentation oc acetic acid is 0.0547M

    

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