SolutionsSolutions

Ask a chemist, they always haveAsk a chemist, they always have

DefinitionsDefinitions

Mixture: several pure substances mixed together Mixture: several pure substances mixed together in an indefinite ratioin an indefinite ratio HomogeneousHomogeneous HeterogeneousHeterogeneous

Solution: a homogenous mixture that form when Solution: a homogenous mixture that form when one or more substances dissolve into another. one or more substances dissolve into another.

Suspensions: cloudy mixtures that form when Suspensions: cloudy mixtures that form when two or more substances mix but do not dissolve.two or more substances mix but do not dissolve.

Emulsions: suspension of 2 liquidsEmulsions: suspension of 2 liquids

Solutes and SolventsSolutes and Solvents

Solution: a homogenous mixtureSolution: a homogenous mixture Solute: thing that dissolvesSolute: thing that dissolves Solvent: thing that does the dissolving Solvent: thing that does the dissolving

(found in the largest amounts)(found in the largest amounts) If the solvent is water, then it is called an If the solvent is water, then it is called an

aqueous solutionaqueous solution

SolubilitySolubility Example: iced teaExample: iced tea

SoluteSolute

sugar sugar

teatea SolventSolvent

waterwater

Solubility: Ionic CompoundsSolubility: Ionic Compounds

Ions form, separate (dissociate) and move Ions form, separate (dissociate) and move throughout the solutionthroughout the solution The forces that hold the ions together are The forces that hold the ions together are

overcome by the ionsovercome by the ions’’ attractions to polar attractions to polar water.water.• Ion- dipole interactionIon- dipole interaction

Because ions are present, ionic solutions Because ions are present, ionic solutions can conduct a current can conduct a current Current is just movement of electronsCurrent is just movement of electrons

Figure 15.1: Dissolving of solid Figure 15.1: Dissolving of solid sodium chloride.sodium chloride.

Solvation animation

Animation with Audio

Figure 15.2: Polar water molecules interacting with positive Figure 15.2: Polar water molecules interacting with positive and negative ions of a salt.and negative ions of a salt.

““Like dissolves likeLike dissolves like”” Typically, hydrogen bonding occurs Typically, hydrogen bonding occurs

between the substance being dissolved between the substance being dissolved and the polar water moleculesand the polar water molecules

Example:Example: Sugar in waterSugar in water Ethanol in waterEthanol in water

Solubility: Polar CompoundsSolubility: Polar Compounds

Figure 15.3: The polar water molecule interacts strongly with Figure 15.3: The polar water molecule interacts strongly with

the polar O—H bond in ethanolthe polar O—H bond in ethanol..

Figure 15.4: Structure of Figure 15.4: Structure of common table sugar.common table sugar.

Get interactions between water molecules the polar Get interactions between water molecules the polar regions on the sugar (the Os) , and some hydrogen regions on the sugar (the Os) , and some hydrogen bonding at the -OH groupsbonding at the -OH groups

““They go together like oil and water.They go together like oil and water.”” (things that don(things that don’’t dissolve or mix)t dissolve or mix)

Anything nonpolar will Anything nonpolar will not mix well with not mix well with anything polaranything polar Examples:Examples:

• Oil spillOil spill• Salad dressingSalad dressing

Can mix when shaken Can mix when shaken (LDF) and then may (LDF) and then may separate out (other separate out (other forces)forces)

How much is too much?How much is too much?

There is a limit to the amount of a There is a limit to the amount of a substance dissolvedsubstance dissolved SaturatedSaturated: the solution holds as much : the solution holds as much

solute as possible solute as possible at that temperatureat that temperature.. UnsaturatedUnsaturated:: solution has not reached the solution has not reached the

limitlimit

Can you have too much? YES!Can you have too much? YES! Supersaturated:Supersaturated: have as much solute have as much solute

dissolved as possible, then cooled and all the dissolved as possible, then cooled and all the solute stays dissolved. solute stays dissolved.

In other words…the solution contains more In other words…the solution contains more dissolved solid than a saturated solution dissolved solid than a saturated solution created at the same temperature.created at the same temperature.

These can begin crystallization of the solute These can begin crystallization of the solute at the slightest changeat the slightest change

Energy changes and SolvationEnergy changes and Solvation

Any chemical change (including solvation) Any chemical change (including solvation) requires a change in energyrequires a change in energy Energy removed from or added to the Energy removed from or added to the

reactants from the surroundingsreactants from the surroundings NaOHNaOH(s)(s) Na Na++ (aq)(aq)+ OH+ OH-- (aq) (aq) ΔΔH= -44.5 H= -44.5 kJ/molkJ/mol

(that(that’’s 44.5kJ released, so exothermic, per mole of NaOH)s 44.5kJ released, so exothermic, per mole of NaOH)• Because you are breaking the ionic bond, energy must be Because you are breaking the ionic bond, energy must be

either released when breaking the bond, or consumed when either released when breaking the bond, or consumed when making the new ionsmaking the new ions

ALL changes in formula indicate a change in energy.ALL changes in formula indicate a change in energy. However, sometimes the energy change is so small, you canHowever, sometimes the energy change is so small, you can’’t t

tell that a change has occurredtell that a change has occurred

Why some coffees Why some coffees ““Put hair on Put hair on your chest.your chest.””

““StrongStrong”” coffee has more coffee has more coffee dissolved in a given coffee dissolved in a given amount (say 1 pot) than amount (say 1 pot) than ““weakweak”” coffee. coffee.

Strong coffee = concentratedStrong coffee = concentrated Weak coffee = diluteWeak coffee = dilute

Concentration: the amount of Concentration: the amount of solute in a given amount of solute in a given amount of solvent (or solution).solvent (or solution).

Molarity (Molarity (MM)) Most common way to express concentration Most common way to express concentration Molarity is the number of Molarity is the number of molesmoles of solute of solute

dissolved in each dissolved in each literliter of solution of solution FormulaFormula

MM = = moles of solutemoles of solute

liters of solutionliters of solution

Dependent on temperatureDependent on temperature The higher the molarity the stronger the The higher the molarity the stronger the

concentrationconcentration

Molality (Molality (MM ))

Another way to calculate concentrationAnother way to calculate concentration Formula Formula

MM = = moles solute . moles solute .

kilograms of solventkilograms of solvent Not dependent on temperatureNot dependent on temperature The higher the molality the stronger the The higher the molality the stronger the

concentrationconcentration

Colligative propertiesColligative properties

In the winter, why do we throw salt when it In the winter, why do we throw salt when it snows?snows?

Why does Emeril add salt to boiling water Why does Emeril add salt to boiling water when cooking pasta? when cooking pasta?

Freezing point depressionFreezing point depression

By adding salt (or other solutes) to water, the By adding salt (or other solutes) to water, the temperature of freezing dropstemperature of freezing drops it freezes at a it freezes at a lower temperature lower temperature • Because H bonding is disturbedBecause H bonding is disturbed• Dependent on how much solute is addedDependent on how much solute is added

Freezing Point Depression CalcsFreezing Point Depression Calcs

Antifreeze protects cars from freezing and Antifreeze protects cars from freezing and overheating. Calculate the freezing point overheating. Calculate the freezing point depression of a solution of 100. g of ethylene depression of a solution of 100. g of ethylene glycol (Cglycol (C22HH66OO22) antifreeze in 0.500 kg of water. ) antifreeze in 0.500 kg of water. KKff

waterwater = = 1.86 1.86 ooC/C/mm

Formula: Formula:

TTff = K = Kffmm ii KKff : : Molal Freezing Point depression constant (Molal Freezing Point depression constant (ooC/C/mm)) i= Pieces that the material dissociates into (for ionic compounds only)i= Pieces that the material dissociates into (for ionic compounds only) (Keep I at 1 (one) for covalent compounds)(Keep I at 1 (one) for covalent compounds)

Freezing Point Depression and Boiling Point Elevation

Solvent Formula Melting

Point (°C)

Boiling Point (°C)

Kf

(°C/m)

Kb

(°C/m)

Water H2O 0.000 100.000 1.858 0.521

Acetic acid HC2H3O2 16.60 118.5 3.59 3.08

Benzene C6H6 5.455 80.2 5.065 2.61

Camphor C10H16O 179.5 ... 40 ...

Carbon disulfide

CS2 ... 46.3 ... 2.40

Cyclohexane C6H12 6.55 80.74 20.0 2.79

Ethanol C2H5OH ... 78.3 ... 1.07

Boiling point elevationBoiling point elevation

By adding salt (or other compounds) to water, By adding salt (or other compounds) to water, the temperature of boiling goes upthe temperature of boiling goes up it boils at it boils at a higher temperaturea higher temperature• Interrupts H bondingInterrupts H bonding• Need more vapor molecules and greater pressure Need more vapor molecules and greater pressure

to get bubbles to formto get bubbles to form• Takes more time to get vapors to add to bubbles Takes more time to get vapors to add to bubbles • The molecules that do get into the bubbles need The molecules that do get into the bubbles need

more energy more energy Dependent on how much solute is addedDependent on how much solute is added

Boiling Point Elevation CalculationsBoiling Point Elevation Calculations

Water with salt added boils at a higher Water with salt added boils at a higher temperature than pure water. By how much will temperature than pure water. By how much will the boiling point change if 100.g of salt is added the boiling point change if 100.g of salt is added to 500. g of water? to 500. g of water? KKbbwaterwater = = 0.52 0.52 ooC/C/mm

Formula: Formula:

TTbb = K = Kbbmm ii

KKbb : : Molal Boiling Point elevation constant (Molal Boiling Point elevation constant (ooC/C/mm))

i= = Pieces that the material dissociates into (for ionic compounds only)i= = Pieces that the material dissociates into (for ionic compounds only) (Keep I at 1 (one) for covalent compounds)(Keep I at 1 (one) for covalent compounds)

Freezing Point Depression and Boiling Point Elevation

Solvent Formula Melting

Point (°C)

Boiling Point (°C)

Kf(°C/

m) (

Kb(°C/

m)

Water H2O 0.000 100.000 1.858 0.521

Acetic acid HC2H3O2 16.60 118.5 3.59 3.08

Benzene C6H6 5.455 80.2 5.065 2.61

Camphor C10H16O 179.5 ... 40 ...

Carbon disulfide

CS2 ... 46.3 ... 2.40

Cyclohexane C6H12 6.55 80.74 20.0 2.79

Ethanol C2H5OH ... 78.3 ... 1.07

Figure 15.10: Pure water.Figure 15.10: Pure water.

Figure 15.9: A bubble in the interior of liquid water surrounded by Figure 15.9: A bubble in the interior of liquid water surrounded by solute particles and water molecules.solute particles and water molecules.

Figure 15.10: Solution (contains solute).Figure 15.10: Solution (contains solute).

Vapor Pressure ReductionVapor Pressure Reduction

Vapor pressure changes as IMFs changeVapor pressure changes as IMFs change For the same reasons boiling point is For the same reasons boiling point is

disturbeddisturbed What would evaporate faster:What would evaporate faster:

Salt waterSalt water Distilled waterDistilled water

WHY?WHY?

Colligative properties interactiveColligative properties interactive