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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