Dear Aspirants ,

If the [acetate ion] = [ acetic acid] then the pH of the buffer is equal to the pKa of the acid The pKa of acetic acid = 4.74. This is the pH you obtained for the buffer.

Therefore the [acetate ion] = 0.20M

Lets begins with example

Molar mass NaC2H3O2.3H2O = 136.08 g/mol

0.65g = 0.65/136.08 = 0.004777 mol dissolved in 25mL solution = 0.025L

Molarity of acetate = 0.004777/0.025 = 0.19 mol / litre or 0.19M solution

That is very close to what was first proposed as the molarity of the acetate ion.

Hope  it will helpful

thanks