Question

A buffer composed of 0.50 mol acetic acid (HC₂H₃O₂) and 0.50 mol sodium acetate (Na⁺C₂H₃O₂^-) is diluted to a volume of 1.0 liter. The pH of the buffer is 4.74. How many moles of NaOH must be added to the buffer to raise its pH to 5.74?

A. 0.25 mol

B. 0.41 mol

C. 0.50 mol

D. 0.55 mol

E. 0.49 mol

Answer 1

               CH₃COOH + NaOH   CH₃COONa + H₂O

Equb moles (at pH 4.74 )          0.50                                0.50

According to Henderson's Equation ,

After adding NaOH :

               CH₃COOH + NaOH   CH₃COONa + H₂O

Equb moles (at pH 4.74 )            0.50                                0.50

after addition of NaOH(pH=5.47)          0.50 - a                           0.50 + a     Here a = increase in moles of salt

According to Henderson's Equation ,

11a = 4.5

a = 0.41 mol

So the number of moles of NaOH added is 0.41 mol