At `100^@C` the vapour pressure of a solution of 6.5 g of a solute in 100 g water is 732 mm. If `k_b = 0.52`, the boiling point of this solution will be

Options

A. `102^@C`
B. `103^@C`
C. `101^@C`
D. `100^@C`

Answer

C

Explanation

Given:`W_B=6.5g,W_A=100g,p_s=732 mm, K_b=0.52, T_b^@ = 100^@C, p^@ = 760 mm`
`(p^@-P_s)/(P^@) = n_2/n_1 implies (760-732)/760 = n_2/(100//18)`
`implies n_2 = (28 xx 100)/(760xx18) = 0.2046` moles
`DeltaT_b= K_b xx m`
`T_b - T_b^@= K_b xx (n_2 xx1000)/(W_A(g))`
`T_b - 100^@C =(0.52 xx 0.2046xx1000)/100 = 1.06`
`T_b = 100+1.06 = 101.06^@C`