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. C 6 H 12 O 6(s)  C 6 H 12 O 6(aq) C 6 H 12 O 6 O HH O H H O HH O H H O HH O HH O H H O H H O H H O H H O HH O HH O HH O HH O HH O H H O HH O H H O HH O HH O H H O H H O H H O H H O HH O HH O HH O HH [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 - Cl - Na + O HH O H H O HH O H H O HH O HH O H H O H H O H H O H H O HH O HH O HH O HH O HH O HH O H H O HH O H H O H H O H H O H H O HH O HH O HH Na + Cl - Na + Cl - O HH O HH O H 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 C 6 H 12 O M NaCl O HH O HH O H H O HH O H H O H H O H H O H H O HH O HH O HH Na + Cl - Na + Cl - O HH O HH O H H O HH O H H O HH O H H O HH O HH O H H O H H O H H O H H O HH O HH O HH O HH C 6 H 12 O 6 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 0 o C!

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) CaCl 2. Ex.(4) If some ethylene glycol - C 2 H 4 (OH) 2 is dissolved in water, then the resulting solution will freeze at a _______________ temperature than normal. lower higher 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 - C 2 H 4 (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 (≈ 15 o F or -10 o C ).

Colligative Properties of Solutions Gin in a freezer!