COLLIGATIVE PROPERTIES

the 4 physical effects solutes can have on solutions

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COLLIGATIVE PROPERTIES- the physical properties of solutions that are affected by the number of particles and not the identification of dissolved solutes

1. BOILING POINT ELEVATION

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Liquids boil when the vapor pressure equals the atmospheric pressure By adding a solute, the temperature at which the liquid boils is higher.

EX: adding salt to water when cooking makes the water boil at a higher temperature. Cooking noodles will cook faster because the water can reach a higher temperature and your noodles won’t be as soggy!

2. FREEZING POINT DEPRESSION

By adding a solute to water, the freezing point is lowered.. EX: salt added to roads makes the water freeze into ice at a lower temperature.

EX: antifreeze is added to a car radiator, so the water will not freeze until it reaches a temperature lower than 0

3. VAPOR PRESSURE LOWERING

Water pressure exerted in a closed container by liquid particles that have escaped the surface and entered the gaseous state.

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by increasing the number of solute particles, the vapor pressure is lowered

4. OSMOTIC PRESSURE

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Diffusion- the mixing of gases or liquids due to random motions Osmosis – different solvent particles cross a semi-permeable membrane from an area of high solvent concentration to one of lower concentration. Movement of water, not the solute!!

1.2 M 0.45 M A B A B

A selectively permeable membrane separates two aqueous solutions of potassium chloride (KCl). On the left side of the membrane is solution A composed of 1.24 M solution. On the right side of the membrane is solution B composed of 0.45 M solution. Which side is most concentrated?

Which side has the most water?

Which way will the water flow?

ELECTROLYTES

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Ionic compounds are electrolytes This means that they dissociate in water to form a solution that conducts electric current

The 4 colligative properties, once again are…

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Increase in bp (bp elevation) Decrease in fp (fp depression) Lowering of vapor pressure Osmotic pressure

MOLARITY

TRY THESE…

DILUTION

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What is the molarity of a solution with 50 g How many milliliters of 2.55M sodium carbonate NaOH is needed to make a 125 dissolved in 2000 mL of mL of a 0.75M NaOH?

water?

M= mol/L 50 g Na 2 CO 3 106 g M 1 V 1 =M 2 V 2 (2.55M)(V1) = (0.75M)(125mL) X 1 mol = .47mol V 1 = 36.8 mL M= .47 mol = .2M

2L