Colligative Properties of Solutions

Colligative Properties of Solutions• All pure liquids have a normal freezing point.

• However, impure liquids (liquid solutions) always freeze at a LOWER temperature than normal.

• The HIGHER the concentration of impurity particles, the lower the freezing point will be.

• the impurities make it harder for the particles of the liquid to arrange themselves in the ordered structure (crystal lattice) that all solids exhibit. Thus, it takes a LOWER temperature than normal to freeze an impure liquid.

• This is called the freezing point depression of solutions.

Colligative Properties of Solutions• Rock salt or super melt are sprinkled on icy sidewalks

which lowers the ice’s freezing point.

Colligative Properties of Solutions• Glucose is a sugar which is a nonelectrolyte.• When dissolved in water, glucose does NOT form ions.• Thus a 1.00 mole of glucose dissolved in water will have

1.00 mole of dissolved particles.

C6H12O6(s) C6H12O6(aq)

C6H12O6 C6H12O6

C6H12O6 C6H12O6

OH H

OH

H

OHH

OH

H

OHH

OHH

OH

H

OH

H

OH

H

OH

H

OH H

OH H

OH H

OHH

OH H

OH

H

OHH

OH

HO

HH

OHHO

H

H

OH

H

OH

H

OH

H

OH H

OH HO

H H

OHH

C6H12O6

C6H12O6

C6H12O6

C6H12O6

[i = 1]

Colligative Properties of Solutions• Sodium chloride is a salt which is an electrolyte.• When dissolved in water, sodium chloride does form ions.• Thus a 1.00 mole of sodium chloride dissolved in water

will have 2.00 moles of dissolved particles.

NaCl(s) Na+(aq) + Cl-(aq)

Na+Cl-Na+Cl-

Cl-Na+Cl-Na+

OH H

OH

H

OHH

OH

H

OHH

OHH

OH

H

OH

H

OH

H

OH

H

OH H

OH H

OH H

OHH

OH H

OHH

OH

H

OHH

OH

HO

H

H

OH

H

OH

H

OH H

OH H

OHH

Na+

Na+

Cl-

Cl-

Cl-

Na+

Na+

Cl-

OHH

OH H

OH

H

[i = 2]

Colligative Properties of Solutions• Which of the following two solutions has more dissolved

particles? • Which of the following two solutions will have a lower

freezing point?

4.0 M C6H12O6 4.0 M NaCl

OH H

OHH

OH

H

OHH

OH

HO

H

H

OH

H

OH

H

OH H

OH H

OHH

Na+

Na+

Cl-

Cl-

Cl-

Na+

Na+

Cl-

OHH

OH H

OH

H

OH H

OH

H

OHH

OH

HO

HH

OHHO

H

H

OH

H

OH

H

OH

H

OH H

OH HO

H H

OHH

C6H12O6

C6H12O6

C6H12O6

C6H12O6

The NaCl solution!

The NaCl solution!

Colligative Properties of Solutions• When making ice cream, salt is added to the ice

surrounding the canister. The added salt lowers the ice’s melting point making the canister colder than 0oC!

Colligative Properties of Solutions• All pure liquids have a normal boiling point.

Q1: At what temperature will a pure liquid boil?

A1: The temperature at which the liquid’s vapor pressure is equal to the current air pressure.

• However, impure liquids (liquid solutions) always boil at a HIGHER temperature than normal.

• The HIGHER the concentration of impurities, the higher the boiling point will be.

• This is called the boiling point elevation of solutions.

Colligative Properties of Solutions• Coolant is added to the water in a car’s radiator which

raises the water’s boiling point.

Colligative Properties of Solutions

Ex.(1) Pure water will boil at a ____________________

temperature than saltwater.

Ex.(2) Pure water will freeze at a ____________________

temperature than saltwater.

Ex.(3) Which 1.0 M aqueous solution would have the lowest

freezing point?

(1) NaCl (2) HCl (3) KCl (4) CaCl2.

Ex.(4) If some ethylene glycol - C2H4(OH)2 is dissolved in

water, then the resulting solution will freeze at a

_______________ temperature than normal.

lower

higher

i = 2 i = 2 i = 2 i = 3

lower

Colligative Properties of Solutions• Airplane’s are deiced with ethylene glycol.

Colligative Properties of Solutions

Ex.(5) If some ethylene glycol - C2H4(OH)2 is dissolved

in water, then the resulting solution will boil at a

_______________ temperature than normal.

Ex.(6) Why will a bottle of wine (12% alc. by vol.) or beer

(3% alc. by vol.) freeze when placed in the freezer

but a bottle of gin (47% alc. by vol.) will not?

_________________________________________

_________________________________________

_________________________________________

higher

The gin has a much higher concentration of

alcohol which lowered its freezing point below

the freezer’s temperature (≈ 15oF or -10oC ).

Colligative Properties of Solutions• Gin in a freezer!