How many grams of sodium acetate, NaC2H3O2, would have to be added to 1.00 L of 0.15 M acetic acid, HC2H3O2, to make a buffer with a pH of 5.00?

1 Answer
anor277
Jun 2, 2018

Approx. 20*g of sodium acetate are required....

Explanation:

We use the buffer equation...

A buffer is prepared when a weak base, and its conjugate acid are mixed together in appreciable quantities to give a solution that resists gross changes in pH...and for such a system...

pH=pK_a+log_10{[[A^-]]/[[HA]]}

For acetic acid pK_a=4.76. And so we fill in the dots...

5.00=4.76+log_10{[[AcO^-]]/[[HOAc]]}

So here log_10{[[AcO^-]]/[[HOAc]]}=+0.24

{[[AcO^-]]/[[HOAc]]}=10^(0.24)=1.74

Now we have been given...[HOAc]=0.15*mol*L^-1...

Thus...[AcO^-]=0.15*mol*L^-1xx10^(0.24)=1.74xx0.15*mol*L^-1

A mass of .....................1.00*Lxx0.261*mol*L^-1xx82.03*g*mol^-1=21.39*g.

Let us check this out....

pH=4.76+log_10{[[0.261*mol*L^-1]]/[[0.15*mol*L^-1]]}=5.00

As required....

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