SOLUTIONS A mixture worth getting your hands wet in.

SOLUTIONSSOLUTIONS

A mixture worth getting your A mixture worth getting your hands wet in.hands wet in.

SOLUTIONS UNIT SKILLSSOLUTIONS UNIT SKILLS

• Determine if a mixture is a solutionDetermine if a mixture is a solution• Describe how various factors affect solubility and Describe how various factors affect solubility and

the rate of solutionthe rate of solution• Interpret data on solubility curvesInterpret data on solubility curves• Distinguish between saturated, unsaturated, Distinguish between saturated, unsaturated,

supersaturated, concentrated, and dilute solutionssupersaturated, concentrated, and dilute solutions• Solve problems that involve concentrations of Solve problems that involve concentrations of

solutionssolutions• Describe the relationship between solute Describe the relationship between solute

concentration and change in the boiling and concentration and change in the boiling and freezing points of a solventfreezing points of a solvent

Solution TerminologySolution Terminology

•Solution– homogeneous mixture

•Solute – substance dissolved in another substance

•Solvent – substance that dissolves the solute

•Aqueous – solution in which water is the solvent

•Tincture – solution in which alcohol is the solvent

Solution CharacteristicsSolution Characteristics•Homogeneous mixtures•The dissolved particles will not settle

out of the solution•Light can pass unobstructed through

the solution•Filtration will not separate out the

solute•Considered to be a single phase even

if started as two different phases

Types of SolutionsTypes of Solutions• Gas Solutions – two or more gases mixed together• Liquid Solutions

A. Solid dissolved in a liquidB. Liquid dissolved in a liquidC. Gas dissolved in a liquid

• Solid Solutions – two or more solids mixed togetherA. Alloy – solid solution of two or more metals

examples:B. Amalgam – alloy in which mercury is one of the

metalsT yp es o f S o lu tio ns

G a s S o lu tio nsT w o o r m o re g a ses

m ixed to g e th er

S o lid d isso lve d in a liq u id L iq u id d isso lve d in a liq u id G a s d isso lve d in a liq u id

L iq u id S o lu tio ns

A llo yS o lid so lu tio n o f tw o

o r m ore m e ta ls

A m a lg amA llo y in w h ich m e rcu ry

is o ne o f th e m e ta ls

S o lid S o lu tio nsT w o o r m o re so lids

m ixed to g e th er

S o lu tio n Typ es

Solubility

• We need to find out about the process of dissolving so we can predict...

• Why certain substances dissolve in water.

Ionic compounds dissolving:

In the case of sodium chloride, as with many other ionic compounds, when they dissolve in water, they disperse randomly and also become strong electrolytes.

Solubility is affected by the strength of the solute-solute attractions as well as the solute-solvent attractions.

Solubility of polar substances

• Water is able to dissolve non-ionic substances also like sugar.

• Also ethanol.• Why? When water is a very polar

molecule.• We have to look at the substance

itself. It must be compatible with water.

The ethanol molecule contains a polar O—H bond.

Ethanol can form

hydrogen bonds with

water molecules.

The polar water molecule interacts strongly with the polar O—H bond in ethanol.

Do you see where the sugar molecule might be attracted to

water?

Can you see any places for water to be attracted to petroleum?

We know from experience that oil and water don’t mix. They are insoluble or immiscible.( 2 liquids that are mutually insoluble)

“Like dissolves like”

Characteristics of Solutions

HomogeneousSolute will not settle out as long as conditions aren’t changed.Light passes throughFiltration will not separateOne phase

http://www.youtube.com/watch?v=NxldP1wK-f4

Examples of types of solutions

State of solution

State of solute

State of solvent

Example

Gas Gas Gas Air, natural gas

Liquid Liquid Liquid Antifreeze in water

Solid Solid Solid Brass

Liquid Gas Liquid Soda, carbonated

Liquid Solid Liquid Seawater, sugar water

SolubilityAmount of solute that can dissolve in a solvent

•Temperature – higher solubility at higher temperatures. Except gases dissolved in a liquid. Behave the opposite way.

•Polarity of solute and solvent. Like dissolves like. Example: vitamins

•Pressure – mainly affects gaseous solutes. Higher pressure more gas can dissolve.

Rate of SolutionRate of Solution How quickly a solute How quickly a solute dissolvesdissolves• Size of the solute particlesSize of the solute particles

• StirringStirring

• Amount of solute already dissolvedAmount of solute already dissolved

• TemperatureTemperature

Solution Concentrations

• We have some very general descriptions:– Saturated: solution contains as much solute as in

can at that temp.– Unsaturated: when more solute can be added and

dissolves– Supersaturated: solution contains more dissolved

solid than saturated solution. Very unstable– Concentrated: relatively large amount of solute

present– Dilute: relatively small amount of solute is

dissolved

• And then some more specific descriptions:– Mass Percent --Density – Molarity– Molality– Normality

Mass Percent

Mass percent = Mass of soluteMass of solution

x 100

Suppose a solution is prepared by dissolving 1.0 g of sodium chloride in 48 g of water. The solution has a mass of 49 g total. Find the mass percent of the solute.

1.0 g solute49 g solution

x 100 = 2.0% NaCl

Although milk is not a true solution, it does contain dissolved sugar called lactose. Cow’s milk typically contains 4.5% by mass of lactose, C12H22O11. Calculate the mass of lactose present in 175 g of milk.

Mass of solution (milk) = 175 gMass percent of solute (lactose) = 4.5%

Mass percent = Mass of soluteMass of solution

x 100%

4.5% = X (unknown g solute)175 g solution

x 100%100%

175 g

X = 7.9 g solute (lactose)

Molarity

The units we show as either:

M

M = Moles solute Liters of solution

Since we deal with solutions a lot, a more convenient measure of concentration is Molarity.

Or mol L

Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution.

M = Moles solute Liters of solution

11.5 g NaOH 1 mol NaOH40.0 g NaOH1.50 L solution

= 0.192 M NaOH

Calculate the molarity of a solution prepared by dissolving 1.56 g gaseous HCl into enough water to make 26.8 mL of solution.

M = Moles solute Liters of solution

1.56 g HCl 1 mol HCl36.5 g HCl26.8 mL solution

= 1.59 M HCl1000 mL 1 L

Molality

m = Moles solute kg solvent

Density

d = Grams solutemL solution

Preparing a Standard Solution

1. Calculate # g of solute.

2. Put a little distilled water in the flask.

3. Put solute in flask, dissolve.

4. Fill to the mark.

Making a Standard Solution

To analyze the alcohol content of a certain substance, a chemist needs 1.00 L of an aqueous 0.200 M K2Cr2O7 solution. Give directions to mix.

1.00 L soln 0.200 mol K2Cr2O7

1 L294.2 g K2Cr2O7 1 mol

=58.8 g K2Cr2O7

3. Put K2Cr2O7 in flask, dissolve.

2. Put small amount of distilled water in 1 L flask.1. Weigh out 58.8 g K2Cr2O7

4. Fill to the mark with distilled water.

DilutionSometimes, concentrated solutions are purchased. Water is added to achieve the desired molarity for a particular solution.

M1V1 = M2V2

Prepare 500. mL of 1.00 M acetic acid (HC2H3O2) from a 17.5 M stock solution.

(17.5 M)V1=(1.00 M)(500 mL)

V1 = 28.6 mL

How many moles of Ag+ ions are present in .025 L of a 0.75 M AgNO3 solution?

.025 L 1 mol Ag+ ions1 mol AgNO3

= .019 mol Ag+

0.75 mol AgNO3

1 L

Remember: 1 mole of AgNO3 = 1 mole Ag+ ions

Properties of Solutions:boiling & freezing points

• What does adding NaCl to a pot of boiling water do?

• Why do we spread “ice melt” on our sidewalks in the winter?

• Why do we add “antifreeze” to our car radiators?

• Adding a solute to a solvent changes the vapor pressure of the solution....thus changing the boiling and freezing points!

Boiling in a pure solvent

Those solvent molecules in the

bubble have enough energy to break all

intermolecular attractions

When a solute is added: It may be

argued that the solute

reduces the number of

solvent molecules

that can get into the bubble.

Thus it takes more energy (heat) to “boil” the solvent....this is the “boiling

point elevation”

Freezing point is also affect by the addition of a solute.

At the point of freezing & melting, the vapor pressures of the solid and liquid are at equilibrium.

Since adding a solute lowers the vapor pressure of a substance, the vapor pressure of a liquid is equal to that of the solid at a lower “temperature”.

These properties— boiling point freezing point vapor pressure osmotic pressure of solvent

--are called

Colligative Properties

Freezing Point DepressionFreezing Point Depression

Normal freezing point occurs at a temperature where the vapor pressure of the solid and liquid are equal to each other.

Tf = Kf m solute

Kf is the freezing point constant for the solvent.

Normal freezing point occurs at a temperature where the vapor pressure of the solid and liquid are equal to each other.

The solid does not form until the temperature is lower than in the pure solvent.

We say that a non-volatile solute depresses the freezing point of a solution and can calculate it with:

The solid does not form until the temperature is lower than in the pure solvent.

11.9 What mass of ethylene glycol (C2H6O2) must be added to 10.0 L water to produce a solution for use in a car’s radiator that freezes at -10.0 oF (-23.3oC)? Assume the density of water is exactly 1 g/mL.

Tf = Kf m solute

T = 23.3oC

Kf = 1.86oC kg/mol

10.0 kg solvent used

23.3oC = (1.86oCkg/mol) m solute

msolute=12.53 mol C2H6O2

kg solvent 10 kg water

= 125.3 mol C2H6O2

125.3 mol C2H6O2

= 7769 g

62 g C2H6O2

1 mole

OsmosisOsmosis

•A semi-permeable membrane separates a solution and pure solvent—allowing the solvent but not the solute to pass.

•Osmosis is the flow of solvent to the solution until the solution reaches equilibrium

•Osmotic pressure is the hydrostatic pressure on the solution and depends on the concentrations….