Question

You wish to make a buffer with pH 7.0. You combine 0.060 grams of acetic acid and 14.59 grams of sodium acetate and add water to yield a total volume of 1 liter . What is the pH? Will this be the useful pH 7.0 buffer you seek?

Answer 1

The pH of the buffer is 7.0 and this pH is not useful to pH 7.0

Step-by-step explanation:

The pH of a buffer is obtained by using H-H equation:

pH = pKa + log [A⁻] / [HA]

Where pH is the pH of the buffer

The pKa of acetic acid is 4.74.

[A⁻] could be taken as moles of sodium acetate (14.59g * (1mol / 82g) = 0.1779 moles

[HA] are the moles of acetic acid (0.060g * (1mol / 60g) = 0.001moles

Replacing:

pH = 4.74 + log [0.1779mol] / [0.001mol]

pH = 6.99 ≈ 7.0

The pH of the buffer is 7.0

But the buffer is not useful to pH = 7.0 because a buffer works between pKa±1 (For acetic acid: 3.74 - 5.74). As pH 7.0 is out of this interval,

this pH is not useful to pH 7.0