Bellwork

Write out a numbered list of steps thatyou could follow to prepare a 1Maqueous solution of KCl.

Colligative Properties of Solutions

The wood frog is aremarkable creaturebecause it can survive beingfrozen. Scientists believethat a substance in the cellsof this frog acts as a naturalantifreeze, which preventsthe cells from freezing. Youwill discover how a solutecan change the freezingpoint of a solution.

Vapor-Pressure Lowering

Colligative properties depend onthe number of dissolved particles.It doesn’t matter what type ofparticle it is.

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Three important colligativeproperties of solutions are•vapor-pressure lowering•boiling-point elevation• freezing-point depression

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In a pure solvent, equilibrium isestablished between the liquid and thevapor.

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In a solution, solute particles reduce thenumber of free solvent particles able toescape the liquid.

Equilibrium is established at a lower vaporpressure.

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The decrease in a solution’svapor pressure is proportionalto the number of particles thesolute makes in solution.

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1 mol glucose = 1 mol particles 1 mol NaCl = 2 mol particles

(1 mol Na+ and 1 mol Cl-) 1 mol CaCl2 = 3 mol particles

(1 mol Ca2+ and 2 mol Cl-)

1 mole of CaCl2 has the most effectbecause it makes more particles

The difference in temperature betweenthe freezing point of a solution and thefreezing point of the pure solvent is thefreezing-point depression.

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The magnitude of the freezing-pointdepression is proportional to thenumber of solute particlesdissolved in the solvent and doesnot depend upon their identity.

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Adding salt to icyroads and sidewalkslowers the freezingpoint of water.

Much or all of theice will melt.

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Boiling-Point Elevation

The difference in temperature between theboiling point of a solution and the boilingpoint of the pure solvent is the boiling-pointelevation.

The same antifreeze added to automobileengines to prevent freeze-ups in winter,protects the engine from boiling over insummer.

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The magnitude of the boiling-pointelevation is proportional to thenumber of solute particlesdissolved in the solvent.

The boiling point of water increases by0.512°C for every mole of particles thatthe solute forms when dissolved in1000 g of water.

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Colligative Properties depend on theamount of dissolved particles

NOT THE TYPE.

Vapor pressure is lowered

Boiling point is elevated

Freezing point is depressed

These are thesame thing. Lowervapor pressure =

higher boilingpoint!!

The temperaturerange over whichwater is a liquid is

increased.