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Home Q & A Board Science-Related Homework Help Chemistry (Moderator: Laser_3)
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julia5192 julia5192
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11 years ago
What is the hydrogen-ion concentration of a solution that is 0.010 M in acetic acid and 0.010 M in sodium acetate? The ionization constant of acetic acid is 1.8 ´  10-5.
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wrote...
#1
11 years ago
the formula is

pH= pKa+ log ([salt]/[acid])

as the concentrations are the same (buffer solution) the pH= pKa+log 1  
and log 1=0   so pH=pKa

pKa= log1/1.8*10^-5=4.744
wrote...
#2
11 years ago
This problem is solved using the Henderson - Hasselbalch Equation:
pH = pKa + log ([A-]/[HA]
where:
[A-] = molar concentration of conjugate base
[HA] = molar concentration of undissociated weak acid.
Note that because the ethanoic acid dissociates very slightly, we can use [CH3COOH] for [HA]

pH = -log(1.8*10^-5) + log (0.01/0.01)
pH = 4.7 + log (1.0)
pH = 4.7+0
pH = 4.7
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