Question

Acetic acid associates in benzene. 160 g of acetic acid when dissolved in 100 g

of benzene raised the boiling point by 035 C. Calculate the vant Hoff factor.[ Given : K b for ben zene = 2× 57 K kg mol-1; nor mal mo lar mass of ace ticacid = 60 g mol-1 ]

Answer 1

Wb = 160 g of acetic acid (solute )
Wa = 100 g of benzene (Solvent )
Delta T_b = 0.35 ⁰C

Vant Hoff factor = i

Given :

K_b for benzene
= 2× 57 Kkgmol^-1
= 114 Kkgmol^-1

Molar mass of acetic acid
= 60 g mol^-1

m = molality
= [(Wb)/(Mb x Wa)]
= [(160 g)/(60 x 100)]
= 160/6000 molal

Formula used -
(Delta T_b) = i (K_bx m)

0.35 = i x 114 x (160/6000 )

Vant Hoff factor (i)

i = ( 0.35 x 6000 )/(114 x 160)
= 2100/6840
= 0.30 Answer