Question

When 25.6 g of sulphur was dissolved in 1000 g of benzene, the freezing point lowered by 0.512 K. Calculate the formula of Sulphur (Sx).

(K_f for benzene 5.12 K kg mol^–1 , Atomic mass of Sulphur = 32 g mol^–1 )

Answer 1

Mass of sulphur (S_x) = 25.6 g

Number of moles of\(\text{ S}_\text{x} = \frac{25.6}{32x}\)

Molality of solution of S_x in \(\text{benzene} = \frac{25.6}{32x}\) 

\(\Delta T_f = 0.512 K \) and K_f (for benzene) = 5.12

\(\Delta T_f = iK_fm\)

\(0.512 = 5.12 \times \frac{25.6}{32 x} \ \ [\because i = 1]\)

\(x = \frac{5.12\times 25.6}{0.512 \times 32}= 8\)

\(\therefore\)  Formula of sulphur is S₈.