Solutions

Unit 8

Solutions

Video 8.1

Solutions

Vapor PressureWhen a partially filled container of a liquid is

sealed, some particles vaporize while some condense. The gas particles exert a pressure on it’s own liquid, called the vapor pressure.

If temperature increases, more gas evolves and Vapor Pressure increases.

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Vapor PressureThe boiling point is

the temperature at which the vapor pressure equals the external pressure and the liquid becomes a gas.

Normal Boiling Point is the temperature at which a substance boils at 1 atm pressure.

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Vapor PressureAt higher altitudes, such as Denver Colorado,

air pressure is much lower due to decreases in amount of air molecules. Therefore, water boils at a lower temperature and food takes longer to cook.

At lower altitudes the opposite is true.

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Vapor PressureUsing Table H answer the following questions:

1. At which temperature will water have the highest vapor pressure: 25, 75, 90 or 120?

2. If the VP of propanone is 90kPa, what is the boiling point?

3. When the temperature of ethanoic acid is changed from 55C to 110C the change in the VP is _______?

4. What are the normal boiling points of all gases listed in table H?

120

52C

80-10 = 70 kPa

55, 79, 100, 118 respectively

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Video 8.2

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Properties of LiquidsSurface Tension: elastic force on the

liquid surface.The stronger the intermolecular force,

the higher the surface tension.

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Properties of LiquidsViscocity: measure of a liquid’s resistance to flow. The greater its intermolecular forces of attraction,

the greater the viscosity, the slower it flows.If you increase the temperature, viscosity

decreases.

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SolutionsSolutions are homogeneous physical

mixtures of two or more pure substances. They should be transparent and pass through a filter.

In a solution, the solute is dispersed uniformly throughout the solvent.Solute: The minor part, get dissolved.Solvent: The major part, does the

dissolving. Water is a universal solvent.

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SolutionsAqueous solutions have a water solvent. The solute can change phase in order to

dissolve.Solids and gases can be solutions too

like air and alloys (steel, brass, jewelry).

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SolubilityIf a solute dissolves in the solvent, it is

soluble. If the solute does not dissolve in the

solvent it is not soluble and forms a solid (precipitate).

Solubility refers to the amount of solute that can dissolve in 100 grams of water.

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Factors that affect solubility:Chemical Nature: Remember the rule: like

dissolves like. Polar solvents dissolve polar solutes only.

Temperature: Increasing the temperature will increase the rate of solubility. (Think of iced tea dissolving sugar versus hot tea; hot tea dissolves faster). However, for gases, the relationship is reversed. If you increase the temperature of a gas, the gases will escape (their solubility will decrease).

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Factors that affect solubility:Pressure: For gases only: if the pressure

is increased, the solubility increases. This is why soda companies package soda under high pressures.

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Soluble or insoluble? Use Table FPotassium

fluorideAmmonium

hydroxideCalcium

carbonateLithium

phosphate

Lead acetateStrontium

sulfateMagnesium

chromateBarium

hydroxideSilver chloride

S

S

I

S

S

I

S

S

I

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Video 8.3

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Types of SolutionsSaturated: solvent holds

as much solute as is possible at that temperature.In Table G, saturated

solutions are on the line.Dissolved solute is in

equilibrium with solid solute particles (some may dissolve and some may precipitate out at the same time).

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Types of SolutionsUnsaturated:

solvent holds less than the maximum amount of solute for that temperature is dissolved in the solvent.In table G,

unsaturated solutions fall under the line.

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Types of Solutions

Supersaturated: solvent holds more solute than is normally possible at that temperature.In table G, supersaturated solutions are

found above the line.These solutions are unstable; crystallization

can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

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Temperature

Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

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TemperatureThe opposite is true

of gases:Carbonated soft

drinks are more “bubbly” if stored in the refrigerator.

Warm lakes have less O2 dissolved in them than cool lakes.

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Gases in SolutionThe solubility of

liquids and solids does not change a lot with pressure.

The solubility of a gas in a liquid is directly proportional to its pressure (increase the pressure on a gas, increase the solubility.)

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Table G Questions1. Which solute is the most soluble at 10C?2. What is the solubility of NaNO3 at 80C?3. How many grams of NaCl dissolve at 30C?4. At what temperature can 30g of NH4Cl dissolve

in 100 grams of water?5. If 10 grams of KI are dissolved in 100 grams of

water at 20C, what type of solution is formed?6. If 38 grams of NH4Cl is dissolved in 100 grams

of water at 20C what type of solution is formed?7. If 10 grams of SO2 are dissolved in 100 grams of

water at 50C what type of solution is formed?

KI

147g

38g

4C

US

S

SS

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Video 8.4

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ConcentrationConcentrated

solutions contain large amounts of solutes dissolved in the solvent.

Dilute solutions contain small amounts of solutes dissolved in solvent.

Which is concentrated?

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ConcentrationOn Table G, concentrated

solutions are near the top and dilute solutions are near the bottom.

You can add more solvent to a solution in order to dilute the solution.

There are many ways to calculate the concentration of a solution.

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mol of soluteL of solution

M =

Molarity (M)

Because volume is temperature dependent, molarity can change with temperature.

The equation can be found on table T.

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Examples1. If 3 moles of NaCl are dissolved in 6L of

water, what is the molarity?

2. If 29 grams of NaCl are dissolved in one liter of water, what is the molarity?

3moles/6L =

29g/58g = 0.5moles

0.5moles/1L =

0.5M

0.5M

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Examples3. If 100 grams of KF are dissolved in 300ml of

water, what is the molarity?

4. Calculate the volume needed to create a 2M solution with 3.5 moles of Li2O.

100g/58.1g =1.72mol

X = 1.75L

1.72mol/.3L =

2M=3.5mol/x

5.7M

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Video 8.5

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Mass Percentage

Mass % of A = mass of solutetotal mass of solution

100

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Calculate the % by mass:1. 25 grams of solute in 250 grams of

solution.

2. 75.5 grams of NaCl in 255 grams of water.

3. 2 moles of NaOH in 250 grams of solution.

25/250 x 100 =

75.5/(255+75.5) x 100 =

2x40g = 80g/250 x 100 =

10%

22%

32%

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Parts per MillionCO concentration over 70 ppm can cause

illness. Over 150ppm can cause death.

Ocean water contains over 35000 ppm of salt.

350ppm of CO2 is considered safe. We are at 380ppm in our atmosphere. Global warming?

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ppm = mass of A in solutiontotal mass of solution

106

Parts per Million

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Find the concentration in ppm:125 grams of solution with 12 grams of

solute.

32.5 grams of NH3 in 200 grams of water.

A solution with 25% solute.

A solution with 60% solvent.

12/125 x 106 =

40/100 x 106 =

32.5/232.5 x 106 =

25/100 x 106 =

1.0 x 105ppm

1.4 x 105ppm

2.5 x 105ppm

4.0 x 105ppm

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Video 8.6

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Colligative PropertiesChanges in colligative properties

depend only on the number of solute particles present, not on the identity of the solute particles.

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Colligative Properties of ElectrolytesSince these properties depend on the number of particles dissolved, solutions of electrolytes (which break down into ions in solution) should show greater changes than those of nonelectrolytes. But it also depends on the Molarity.

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Boiling Point Elevation and Freezing Point DepressionNonvolatile solute-solvent interactions also cause solutions to have higher boiling points and lower freezing points than the pure solvent.

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Examples1. Which

compound when dissolved in water, will have the highest boiling point?

a. CaCl2

b. NaIc. C6H12

2. Which compound when dissolved in water, will have the lowest freezing point?

a. 1M NaOHb. 2M NH3

c. 0.5M Mg3N2

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