Question

You decide to use formic acid 1.5l of 70mM buffer and you find the concentrationsto be 0.025M of formic acid and 0.045M of its conjugate base, you find that you can buy 19M formic acid from a chemical company.

a) what volume of 19M formic acid should you start with?

b) Would you make your desired buffer by adding strong acid (0.5 M HCl) or strong base ( 0.5M NaOH) why?

c) How many mL of either the strong acid or the strong base would you need to add?

Answer 1

a). Given molarity of Formic acid = 19 M

Required molarity of Formic acid = 1.51 M

Required volume of Formic acid = 70 mM

Initial volume of 19 M has to taken is = X

19*X = (1.51* 70)

X = (1.51* 70)/19

= 5.56 mM

Volume of required Formic acid = 5.56 mM

b). The desired buffer will be prepared by the addition of strong base (0.5 M of NaOH). Because of this addition the weak acid forms a buffer which contains (weak acid + its salt with Strong base).

But addition of strong acid to formic acid will results no formation of buffer.

c). Concentration of Formic acid = 1.51 M

Volume of Formic acid = 70 mM

Concentration of NaOH = 0.5 M

Required Volume of NaOH = Y

0.5*Y = (1.51*70)

Y = (1.51*70)/0.5

= 211 mM = 9393.9 mL

Thus 9393.9 mL of Strong base required to to get desired buffer