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Chemistry PH of Buffers

Chemistry
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A buffer is prepared by adding 0.95 mol of acetic acid CH3COOH and 4.25 mol of sodium acetate NaCH3COO to enough water to make a 5.0 L solution. What is the pH of the buffer? The ionization constant for acetic acid is 1.8 × 10−5 .

Feb 28th, 2015

                     CH3COOH <======> H+ + CH3COO-

Initial              0.19M                          0            0.85M

Change  -x                             +x             +x

Equilibirum    0.19 - x                       x           0.85 +x

1.8e-5 = (0.85x+x^2) / (0.19 -x)

3.41e-6 -1.8e-5x = 0.85x + x^2

0 = x^2 + 0.849982 - 3.41e-6

x = 0.0000040118307272

pH = - log(0.0000040118307272)

pH = 5.4

Feb 28th, 2015

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