Substances a and b are both volatile liquids with p*a = 300 torr, p*b = 250 torr, and kb = 200 torr (concentration expressed in mole fraction). when xa = 0.9, bb = 2.22 mol kg−1, pa = 250 torr, and pb = 25 torr. calculate the activities and activity coefficients of a and b. use the mole fraction, raoult's law basis system for a and the henry's law basis system (both mole fractions and molalities) for b.

Calculating activity and activity coefficient:

I. using mole fraction and Raoult's law for a:

Activity α

and activity of a = activity coefficient of a x mole fraction of a

αa = γa . xa

γa = αa/xa = 0.83/0.90 = 0.926

II. using the henry's law basis system and:

1. Mole fraction:

αb = Pb/Kb = 25 torr/ 200 torr = 0.13

αb = γb . xb

γb = αb/xb = 0.13/ 0.1 = 1.3

2. Molality:

K*b = Xa.Ma.b0.Kb

(Xa, b0 and Kb are known)

Ma = Xb/Xa.bb

K*b = Xa.Ma.b0.Kb = Xa.Xb.b0.Kb/Xa.bb = Xb.b0.Kb/bb

K*b = (0.1)(1.0 mol/Kg)(200 torr)/ (2.22 mol/Kg) = 9.0 torr

αb = Pb/K*b = 25 torr / 9 torr = 2.8

αb = γb.bb/bo

γb = αb.bo/bb = (1.0 mol/Kg)(2.8) / (2.22 mol/Kg) = 1.3

c. because step up transformer steps up the input voltage i.e increases the input voltage  

the number of turns are greater on the secondary side of step up transformer  

transformer does not handle dc current

the answer is b & c i believe : )