Unit 6- Unit 6- SolutionSolution

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Unit 6- Unit 6- SolutionSolution

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Classification of MatterClassification of Matter

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Focus on MixturesFocus on Mixtures

• Mixtures- Can be separated by physical means

into pure compounds or elements– Homogeneous Mixture-

– Heterogeneous Mixture-

• Classify: salt water, cinnamon and sugar, black coffee, Pepsi.

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Homogeneous Vs Heterogeneous

Mixtures

Homogeneous Vs Heterogeneous

Mixtures

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Which is more likely to form homogeneous

mixtures?

Which is more likely to form homogeneous

mixtures?• Mixtures composed of small particles?• Mixtures made up of large particles?

When particles of the substances making up a mixture are small, they can be more uniformly mixed, or intermingled. Thus, there is a relationship between particle size and the uniformity of the mixture.

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Solutions, Suspensions, Solutions, Suspensions, and Colloidal Dispersionsand Colloidal Dispersions

• Solution- homogeneous mixture whose particles are extremely small in size- individual molecules, atoms, or ions.

• Suspension- heterogeneous mixture in which one or more of the substances is relatively large. Unless a suspension is stirred or shaken, the large particles sooner or later settle out.

• Colloidal Dispersion- heterogeneous mixture in which the particles of one or more of the substances are smaller than those in suspensions, but larger than those in solutions. The particles are large enough to scatter light- Tyndall effect, but too small to filter out.

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Classification of MatterClassification of Matter

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Focus on SolutionsFocus on Solutions

• Solutions are often homogeneous mixtures of two substances. Usually, one of the substances is considered to be dissolved in the other.

SoluteSolute =

SolventSolvent =

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Consider GatoradeConsider Gatorade1. The solution is a homogenous mixture.2. The dissolved particles (sugar, electrolytes) will

not come out of solution no matter how long the solution is allowed to stand.

3. The solution is transparent- the dissolved particles are too small to be seen.

4. Because of the small size of the dissolved particles, the solution will pass through the finest of filters.

5. A solution is a homogeneous mixture that is considered to be a single phase even though the compounds may have been in different phases before the solution was formed.

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Aqueous solutions = water is considered to be the

solvent.

Aqueous solutions = water is considered to be the

solvent.

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Types of SolutionsTypes of Solutions1. Gas- gas or vapors dissolved in one

another- • Air- comprised primarily of O2 and N2

2. Liquid solutions- solvent and solution are liquids; solute can be solid, liquid, or gas

– vinegar- acetic acid and water, – soft drinks – CO2 and sugar with H2O– Miscible- two liquids that dissolve in each other

in all proportions- alcohol and water– Immiscible- liquids that do not dissolve in each

other to any degree- water and oil

3. Solid- two solids uniformly mixed- alloys- Brass- Cu and Zn.

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Solubility of a SoluteSolubility of a Solute•

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Ionic Compounds Dissociate into IonsCovalent (Molecular) Compounds

Dissolve

Ionic Compounds Dissociate into IonsCovalent (Molecular) Compounds

Dissolve

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Degree of Solubility= How Much Dissolves

Degree of Solubility= How Much Dissolves

1. • “Likes dissolve likes”

2.

3.

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The effect of pressure on the solubility of a gas

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Factors Affecting the Rate of Solubility

= How Quickly it Dissolves

Factors Affecting the Rate of Solubility

= How Quickly it Dissolves

• Rate of solution- a measure of how fast a substance dissolves

1. 2. 3. 4.

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Solubility and the Nature of a Solvent and a SoluteSolubility and the Nature of a Solvent and a Solute

• What holds liquids and solids and to some extent gases together?

• What happens when a solid dissolves in a solvent to form a solution?

– In order for a solvent to dissolve a solute, the particles of the solvent must be able to separate the particles of the solute and occupy the intervening spaces.

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Polar Vs Nonpolar Solvents and Solutes

Polar Vs Nonpolar Solvents and Solutes

• Polar solvents can effectively separate the molecules of other polar substances.– EtOH and Water– NaCl and Water

• Positive ions are attracted to negative end of solvent molecules. Negative ions are attracted to the positive ends of solvent molecules.

• Dissociation-

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• Nonpolar substances do not dissolve in polar solvents.– Oil and water don’t mix– Butter doesn’t dissolve well in water– Oil/fat have no attraction for polar molecules–

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Soap and DetergentsSoap and Detergents

• Surfactants- salts of organic acids having large hydrocarbon like groups.

• Soil and dirt are usually held in place by a thin layer of greasy material. Since this layer is nonpolar, the hydrocarbon tails of the detergent ions dissolve in it. The ionic heads of the detergent are hydrated by the water.

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Energy Changes During Solution Formation

Energy Changes During Solution Formation

• Solid dissolves in a liquid- energy from the heat in the liquid is often required to break the forces of attraction in the solid.– Endothermic =

– NH4NO3 dissolving in water.• Most cases in which a solid dissolves in a liquid are

endothermicendothermic.

– Exothermic-

• KOH, NaOH, CaCl2 dissolving in water.

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Solubility Curves and Solubility Tables

Solubility Curves and Solubility Tables

• What is a major variable we can easily control that affects the solubility of a solid?

• • Solubility Curve- shows how much solute

will dissolve in a given amount of solvent over a range of temperatures. (Table G)

• Describe generally what you notice about the solids and their solubilities relative to the temperature of water in the solubility curve.

• NaCl, SO2, HCl, NH3

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Table G: Solubility Curves

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Concentration of a Solution

Concentration of a Solution

• Concentration =

• Is there a limit to how much Gatorade can be put into water?– Dilute solution- one in which the amount of

solute dissolved is small in relation to the amount of solvent.

– Concentrated solution- one in which a relatively large amount of solute is dissolved.

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• Saturated – • (REFER TO TABLE G)

– Solution equilibrium = the rate at which the undissolved solute goes into solution equals the rate at which the dissolved solute drops out of solution.

• Therefore, NO NET CHANGE in amount dissolved.

• Unsaturated-

• Supersaturated-

• UNSTABLE – easily changed to a saturated solution by causing excess solute to precipitate out of solution.

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Saturated and Saturated and Unsaturated Vs Dilute and Unsaturated Vs Dilute and

ConcentratedConcentrated

KClO3 10oC 5g in 100g of water =

NaNO3 10oC 5g in 100g of water =

NaNO3 10oC 80g in 100 g of water =?KI 10oC 80 g in 100g water =?

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MolarityMolarity

• A method of expressing concentration of a solute in a solvent.

Molarity =

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MolarityMolarity

1 M glucose solution = 1 mole of glucose

Liter of Solution1M NaCl = 1 mole Na+ and 1 mole Cl-

liter of solution liter of solution

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Molarity- Example Molarity- Example ProblemsProblems

• A chemistry teacher needs to make 500. mL of dilute hydrochloric acid. He puts 0.050 moles of HCl in 500. mL of solution. What is the concentration of the solution?

• A household cleaner contains 10.0 g NaOH in a 0.100L solution. What is the molarity of the cleaning solution?

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Making a SolutionMaking a Solution1. Determine the mass of the solute needed

and measure on a balance.2. Pour the solute into the proper size

volumetric flask.3. Add enough distilled water to make the

necessary amount of solution.4. Cover the volumetric flask and mix

completely by inverting.

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Molarity Example ProblemMolarity Example Problem

• A student needs to use 0.50 M copper (II) sulfate for a lab. How many grams of copper (II) sulfate pentahydrate must be used to make 250. mL of solution? Briefly describe how the solution would be made.

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Molarity by DilutionMolarity by Dilution

• Less concentrated solutions may be prepared from concentrated solutions using a dilution formula.

WhereM1 describes the molarity of the stock

solutionV1 is the volume of the stock solution

M2 and V2 describe the molarity and volume of the more dilute solution you’re making

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Making a DilutionMaking a Dilution

• 1. Determine the volume of concentrated solution needed and measure in a graduated cylinder or volumetric pipet.

• 2. Pour the more concentrated solution into the proper size volumetric flask.

• 3. Add enough distilled water to make the necessary amount of solution.

• 4. Cover the volumetric flask and mix completely by inverting.

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Dilution Problem ExampleDilution Problem Example

• 0.10M HCl is needed for a lab. How would 250. mL of 0.10 M HCl be prepared from 6.0 M HCl stock solution?

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MolalityMolality

• Molality (m) = the number of moles of solute dissolved in each kilogram of solvent.

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Example Molality ProblemExample Molality Problem

• Calculate the molality of a solution prepared by dissolving 58.44 g of NaCl in 500. g of water.

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Quick Review of Quick Review of Electrolytes Vs Non Electrolytes Vs Non

ElectrolytesElectrolytes

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Colligative PropertiesColligative Properties

• A property that depends on the amount of solute particles but is independent of their identity. In other words, how much, not what it is.

1. Vapor Pressure- solute molecules take up space, preventing some molecules from leaving the liquid.

2. Osmotic Pressure- pressure required to prevent osmosis. Adding a solute to a solvent increases the osmotic pressure of a solution.

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Vapor PressureVapor Pressure Osmotic PressureOsmotic Pressure

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Why it’s a bad idea to drink seawater!

Why it’s a bad idea to drink seawater!

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3. Boiling Point Elevation- related to vapor pressure reduction. Higher temperatures are necessary to get solvent molecules up into the gas phase. When vapor pressure equals atmospheric pressure, the substance boils. If vapor pressure is reduced by the addition of a solute, more energy is required to get the substance to boil.

4. Freezing point depression- similar to boiling point elevation. Solute molecules prevent the formation of intermolecular forces between solvent molecules forming the solid phase.

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The Effect of a Solute on The Effect of a Solute on Vapor PressureVapor Pressure

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Boiling Point ElevationBoiling Point Elevation• The amount by which the temperature of a

solution increases as a result of addition of a solute is called “boiling point elevation” or Tb

Tb is directly proportional to molality

Where Kb = molal boiling point constant

m = molality of the solution d.f. = dissociation factor (electrolytes

only)

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Example Boiling Point Example Boiling Point ElevationElevation

• How many grams of benzoic acid (C7H6O2) must be dissolved in 79.1 g of ethanol to raise the boiling point by 4.00oC? Kb for ethanol is 1.20oC/m.

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Freezing Point DepressionFreezing Point Depression

Where Kf = molal freezing point

depression constant (dependent on solvent)m = molality of the solution

d.f. = dissociation factor (electrolytes only)

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Example Freezing Point Example Freezing Point DepressionDepression

• What is the freezing point of a 5.0 m solution of sucrose? Would it be different for a 5.0 m solution of sodium chloride? Why?

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Example Freezing Point Example Freezing Point DepressionDepression

• A solution of a molecular, nonvolatile solute is prepared as follows: 90 g of solute is dissolved in 250 g of water. The freezing point of the solution is –3.72oC.

Based on the freezing point lowering, what is the molarity of the solution?