Question

4-(N-Morpholino) butanesulfonic acid (FW223.29), MOBS, has a pKa value of 7.48. Calculate how many milliliters of 0.626 MKOH should be added to 5.00 g of MOBS to give a pH of 7.40.

Answer 1

this will turn out a bufer

pH = pKa + log(Conjguate/Acid)

pkA = 7.48

conjugate = MV = 0.626*V

mol of acid = mass/MW = 5/223. =0.02242152 mol of acid

then

acid = 0.02242152 - 0.626*V

pH = pKa + log(Conjguate/Acid)

7.4 = 7.48 + log(0.626*V/ (0.02242152 - 0.626*V))

(0.626*V)/ (0.02242152 - 0.626*V) = 10^(7.4-7.48)

0.626*V = 0.831763*(0.02242152 ) - 0.626*0.02242152 V

(0.626+0.01403)V = 0.831763*(0.02242152 )

V = 0.831763*(0.02242152 ) /(0.626+0.01403) = 0.02913830L

V = 29 ml