Question

The acetic acid/acetate buffer system is a common buffer used in the laboratory. To prepare an acetic acid/acetate buffer, a technician mixes 32.6 mL of 0.0824 M acetic acid and 20.0 mL of 0.120 M sodium acetate in a 100 mL volumetric flask and then fills with water to the 100 mL mark. How many moles of acetic acid are present in this buffer? acetic acid: How many moles of sodium acetate are in the buffer? sodium acetate:

Answer 1

Ans :-

While mixing the solution of Acetic acid and Sodium acetate to makes buffer, number of moles after the addition of 100 mL water remains same as the initial moles. Only Molarity of acetic acid and sodium acetate changes or decreases with addition of water. Therefore,

Given,

Molarity of acetic acid (CH₃COOH) = 0.0824 M

Volume of acetic acid solution = 32.6 mL = 0.0326 L

Because,

Molarity of the solution = Number of moles of solute / Volume of the solution in Liter

So,

Number of moles of CH₃COOH in buffer = Molarity x Volume of solution in L

= 0.0824 M x 0.0326 L

= 0.002686 mol

Similarly,

Given,

Molarity of Sodium acetate (CH₃COONa) = 0.120 M

Volume of Sodium acetate solution = 20.0 mL = 0.020 L

Because,

Molarity of the solution = Number of moles of solute / Volume of the solution in Liter

So,

Number of moles of CH₃COONa in buffer = Molarity x Volume of solution in L

= 0.120 M x 0.020 L

= 0.0024 mol

So,

Number of moles of acetic acid in buffer = 0.002686 mol and Number of moles of sodium acetate in buffer = 0.0024 mol