Molal depression constant $(K_{f})$ is dependent on

The addition of $0.643 \,g$ of a compound to $50 \,mL$ of benzene (density $= 0.879 \,g \,mL^{-1}$) lowers the freezing point from $5.51^{\circ}C$ to $5.03^{\circ}C$. If the freezing point constant,$K_f$ for benzene is $5.12 \,K \,kg \,mol^{-1}$,the molar mass of the compound is approximately $..... \,g \,mol^{-1}$.

Arrange the following solutions in order of decreasing freezing points:
$(a) \ 0.075 \ M \ CuSO_4$ $(b) \ 0.060 \ M \ (NH_4)_2SO_4$
$(c) \ 0.14 \ M \ urea$ $(d) \ 0.04 \ M \ MgCl_2$

Ethylene glycol is used as an anti-freezing agent. Calculate the amount of ethylene glycol to be added to $4 \ kg$ of water to prevent it from freezing at $-6 \ ^{\circ}C$. ($K_f$ for water $= 1.85 \ K \ kg \ mol^{-1}$) (molar mass of $(CH_2OH)_2 = 62 \ g \ mol^{-1}$) .......... $g$.

During the freezing of a solution at its freezing point,which of the following equilibria exists?

If the freezing point of an aqueous urea solution is $271.14 \ K$ at $1 \ \text{atm}$ pressure (given $K_f$ of water = $1.86 \ K \ kg/mol$),then what is the mole fraction of urea in this solution? (Freezing point of pure water is $273 \ K$)