Question

4.
Which of the following aqueous solution will have the
highest freezing point?


(1) 0.1 m NaCl solution (2) 0.1 m Sugar solution
(3) 0.1 m MgCl, solution (4) 0.1 m AlCl2 solution​

Answer 1

When solute is added in a solvent ,the freezing point of the solution lowers compared to the pure solute..let ,here the solutions are aqueous solutions of respective solute…so the freezing point of these solutions are below 0 degree centigrade(freezing point of water at 1 atm pressure).

Now the lowering of freezing point is a colligative property .so the lowering of freezing point depends on the number of particle (number of solute particle).. With increase of number of particles, the freezing point decreases..As the concentration of all solutions are same ,for a fixed amount of these solutions the number of solute molecules should be same.. But ionic compounds like sodium chloride,barium chloride and ferric chloride are dissociated in aqueous medium and each forms 2,3 and 4 particles respectively in the medium..but covalent glucose molecute does not get dissosiated or ionised. Hence 0.1(M) solution of glucose,NaCl, BaCl2 and FeCl3 contain 0.2(M),0.1(M),0.3(M) and 0.4(M) particles of respective solutes(for 1 litter solution).As FeCl3 solution contains maximum number of particles ,its freezing point should be lowest and glucose solution contains minimum number of solute particles, its freezing point should be highest..