Solutions!

Classification of Matter Matter Pure Substances ElementsCompounds Mixtures HomogeneousMixturesHeterogeneousMixtures Also called solutions Also called suspensions

Heterogeneous Mixtures See visibly different regionsSee visibly different regions –Granite –Dirt –Cereals –Oil & Vinegar See a boundarySee a boundary –Ice cube in water

Homogeneous Mixtures Particles are very small – on the atomic scaleParticles are very small – on the atomic scale –Can’t see the particles –Can’t sort the particles –Can’t get trapped by filter –Can’t scatter light Particles are evenly distributedParticles are evenly distributed Particles do not separateParticles do not separate Liquid & gas phase solutions look translucentLiquid & gas phase solutions look translucent

source CuSO 4 (aq) Which is a solution & how do you know?

Solution A homogeneous mixture of 2 or more substances in a single physical state (phase).A homogeneous mixture of 2 or more substances in a single physical state (phase). Exist in all 3 phases.Exist in all 3 phases.

Parts of a Solution SoluteSolute = dissolved substance. SolventSolvent = dispersing medium.

Identify the solute and solvent in each picture.

Solute = ? Solvent = ?

Hints to identify solute & solvent SoluteSolute – changes phase, substance you have less of SolvenSolvent – substance you have the most of, maintains phase

Aqueous Solutions WaterWater is the solvent. Transition metalsTransition metals form brightly colored solutions.

Solutions occur in all 3 phases! SoluteSolventExample GasGasAir LiquidGas Water Vapor in Air SolidGasMothballs GasLiquid Seltzer Water LiquidLiquid Antifreeze in radiator SolidLiquid Salt water GasSolid H 2 in Pd metal LiquidSolid Fillings: Hg in Ag SolidSolid Alloys: Brass, etc.

Gas dissolved in a solid

CO 2 in and out of water When you see bubbles, it’s a mixture not a solution! Solution Mixture

Alloys

Sublimation

Soluble SolubleSoluble – capable of being dissolved. solubleA substance that dissolves in another substance is soluble in that substance.

Insoluble A substance that does not dissolve in another substance.

Amounts that can dissolve SolubilitySolubility = maximum amount of 1 substance that will dissolve in a given amount of another substance. LIMITSLIMITS to the amounts of most liquid or solid solutes that will dissolve in a given solvent. TemperaturepressureTemperature and pressure can affect solubility.

Factors that affect the rate of dissolving Rate of dissolving is different from the amount that will dissolve!Rate of dissolving is different from the amount that will dissolve! Rate is how fast. Several factors influence rate of dissolving.Rate is how fast. Several factors influence rate of dissolving. –Temperature –Stirring or Agitation –Surface Area of Solute –Amount of solute already dissolved.

Dissolving Dissolving is a physical change.Dissolving is a physical change. All physical & chemical changes are accompanied by changes in energy.All physical & chemical changes are accompanied by changes in energy.

Equations for Dissolving C 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq) NaCl(s)  Na + (aq) + Cl - (aq)

source Covalent substances dissolve to produce molecules in solution.

Ionic substances dissolve to produce ions in solution. Movie: Dissolution of NaCl Movie: Dissolution of NaCl

Solvation Interaction between the solvent molecules and the solute particles. Solute particles are surrounded by solvent particles in the dissolving process.Interaction between the solvent molecules and the solute particles. Solute particles are surrounded by solvent particles in the dissolving process. Solute particles may be ions, polar molecules, or nonpolar molecules.Solute particles may be ions, polar molecules, or nonpolar molecules. Solvent molecules may be polar or nonpolar.Solvent molecules may be polar or nonpolar.

Hydration Specific name for the solvent- solute interaction when the solvent is water.Specific name for the solvent- solute interaction when the solvent is water.

Hydration of chloride ion. Also called a molecule-ion interaction.

The solute- solvent interaction must be greater than the interaction between solute particles for dissolving to occur. Molecule-ion interaction

What about when covalent substances dissolve? Covalent substances can be polar or nonpolar. General rule: Like Dissolves Like. H 2 O is a very polar solvent, so it tends to dissolve polar solutes. Oil is nonpolar: oil does not dissolve well in water. Ionic substances will dissolve in polar solvents.

Vocabulary Interlude MiscibleMiscible: two liquids that will mix in any amounts. –Water and ethanol are miscible in all proportions. ImmiscibleImmiscible: Liquids that cannot mix –Oil and water are immiscible.

Solvation in different systems.

Solubility Amount of solute that will dissolve in a specific solvent at a given TEMPERATURE and PRESSURE.Amount of solute that will dissolve in a specific solvent at a given TEMPERATURE and PRESSURE. Determined experimentally.Determined experimentally. Units:Units: grams solute per 100 grams solvent grams solute per 100 grams solvent

Solubility Curves of Selected Solids Solubility traces for most but not all solids have +’ve slopes. The hotter the solvent, the more solute dissolves.

Solubility Curves Solubility Curves

Why do we heat the water up when making rock candy?

Solubility Curves of Selected Gases Solubility traces for all gases have –’ve slopes. Why do fish like cold water?

Why do you see bubbles form on the side of the beaker as the water warms up? (It’s not hot enough to boil.)

Oil & H 2 O are immiscible.

Types of Solutions Matter Pure Substances ElementsCompounds Mixtures Homogeneous Mixtures = Solutions Conduct current Nonconductor Heterogeneous Mixtures

Electricity What do you need to conduct electricity?What do you need to conduct electricity? Mobile charged particles!!!!

Vocabulary Interlude ElectrolyteElectrolyte: A substance that dissolves in water to form a solution that conducts electricity. (There are ions in the solution.) NonelectrolyteNonelectrolyte: A substance that dissolves in water to form a solution that does not conduct electricity. (There are neutral molecules in solution.)

Electrolyte vs. Nonelectrolyte Which solution conducts a current?

Dilute vs. Concentrated Tell you relative amount of solute in solvent. ConcentratedConcentrated – relatively large amounts of solute. DiluteDilute – relatively small amounts of solute.

Which solution is the most dilute? The most concentrated? How do you know? The stronger the color, the more concentrated the solution.

Which solution is more concentrated? More dilute? number of solute particles What can you say about the number of solute particles in pictures b and c? It’s the same!

Unsaturated Solution lessHas less solute than the maximum amount that will dissolve at that temperature and pressure.

Saturated Solution No more solute will dissolve in it at that temperature & pressure.No more solute will dissolve in it at that temperature & pressure. Solubility = amount of solute required to form a saturated solution.Solubility = amount of solute required to form a saturated solution.

The solution is saturated when the solute stops dissolving.

Dynamic Equilibrium = Saturated Solution Rate of dissolving = Rate of recrystallization. Microscopic level: Rate of dissolving = Rate of recrystallization. No apparent change. Macroscopic level: No apparent change.

Supersaturated Solution moreContains more solute than a saturated solution. VERY unstable. Have to be clever to make them up. Sodium Acetate Solution Sodium Acetate Solution Heat Pack Heat Pack Temperature

Testing for saturation: Throw a crystal of the solute into the solution and see what happens.

3 possible results: Crystal dissolvesCrystal dissolves No apparent change in crystalNo apparent change in crystal Bam! Suddenly have lots of solid solute in beaker.Bam! Suddenly have lots of solid solute in beaker. Unsaturated solution. Saturated solution. Supersaturated solution.

What kind of solution was this?

How do the terms saturated, unsaturated & supersaturated fit in with the solubility curves? Saturated solutions have maximum solute that will dissolve at that temperature. Points on traces represent saturated solutions. All points above a trace represent supersaturated solutions of that solute. All points below a trace represent unsaturated solutions of that solute.

AA BB CC DD Characterize points A, B, C, D with respect to KNO 3 trace using the terms dilute & concentrated, and saturated, unsaturated, or supersaturated. A = concentrated & supersaturated. D = dilute & unsaturated.

Summary of Dissolving Occurs at the surface of the solid.Occurs at the surface of the solid. Involves an interaction between the solute and the solvent.Involves an interaction between the solute and the solvent. Interaction is called “solvation.”Interaction is called “solvation.” If water is the solvent, the interaction is called “hydration.”If water is the solvent, the interaction is called “hydration.” Involves changes in energy.Involves changes in energy.

Solubility Information Often presented in graphs Show the number of grams of a substance that can be dissolved in water between 0 o C and 100 o C. Each trace represents a saturated solution. –The space above each trace represents supersaturated solutions. –The space below each trace represents unsaturated solutions.

Solubility Graphs Some traces have positive slopes; some are negative. Most solidsMost solids have a positive slope – the hotter the water, the more solute dissolves. All gasesAll gases have a negative slope – the hotter the water, the less gas dissolves. –The colder the water, the more gas dissolves.