Question

If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water $$\left( {\Delta {T_f}} \right),$$  when 0.01 mol of sodium sulphate is dissolved in 1 kg of water, is$$\left( {{K_f} = 1.86\,K\,kg\,mo{l^{ - 1}}} \right)$$

A. 0.372 $$K$$
B. 0.0558 $$K$$  
C. 0.0744 $$K$$
D. 0.0186 $$K$$
Answer :   0.0558 $$K$$
Solution :
$$\eqalign{ & {\text{Sodium sulphate dissociates as }} \cr & N{a_2}S{O_4}\left( s \right) \to 2N{a^ + } + SO_4^{ - - } \cr & {\text{hence van't}}\,{\text{hoff}}\,{\text{factor}}\,\,i\, = \,3 \cr} $$
$${\text{Now}}\,\Delta {T_f} = i\,{k_f}.m = 3 \times 1.86 \times 0.01$$       $$ = 0.0558\,K$$

Releted MCQ Question on
Physical Chemistry >> Solutions

Releted Question 1

An azeotropic solution of two liquids has boiling point lower than either of them when it

A. shows negative deviation from Raoult’s law
B. shows no deviation from Raoult’s law
C. shows positive deviation from Raoult’s law
D. is saturated
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Releted Question 2

For a dilute solution, Raoult’s law states that :

A. the lowering of vapour pressure is equal to the mole fraction of solute.
B. the relative lowering of vapour pressure is equal to the mole fraction of solute.
C. the relative lowering of vapour pressure is proportional to the amount of solute in solution.
D. the vapour pressure of the solution is equal to the mole fraction of solvent.
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Releted Question 3

When mercuric iodide is added to the aqueous solution of potassium iodide then

A. freezing point is raised.
B. freezing point is lowered.
C. freezing point does not change.
D. boiling point does not change.
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Releted Question 4

Which of the following $$0.1 M$$  aqueous solutions will have the lowest freezing point?

A. Potassium sulphate
B. Sodium chloride
C. Urea
D. Glucose
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