Question

What relative masses of dimethyl amine and dimethyl ammonium chloride do you need to prepare a buffer solution of pH = 10.27?

Express your answer using two significant figures.

Answer 1

dimethyl amine Kb value =5.9 x 10^-4

pKb = -log (5.9 x 10^-4)

        = 3.23

(CH3)2 NH + HCl ---------------------->   (CH3)2 NH2+Cl-

dimethyl amine                                   dimethyl amine chloride

it is basic buffer basic buffer pH

pH = 14 - {pKb + log [salt/base]}

10.27   = 14 - {3.23 +log [salt/base]}

{3.23 +log [salt/base]}   = 3.73

log [salt/base] = 0.5

salt / base = 3.16

dimethyla ammonium chloreide moles (salt) = 3.16 x dimethyl amine (base) moles

weight of salt / 83.5 = 3.16 x weight of base / 47

weight of base / weight of salt = 0.178

dimethyl amine mass / dimethyl ammoonium chloride = 0.178 = 0.18

relative mass = 0.18