Solutions Classification of Matter Pure Substances Elements Compounds

Solutions!

Classification of Matter Pure Substances Elements Compounds Mixtures Homogeneous Mixtures Heterogeneous Mixtures Also called solutions suspensions

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

Parts of a Solution • Solute = dissolved substance. • Solvent = dispersing medium.

Identify the solute and solvent in each picture.

Solute = ? Solvent = ?

Hints to identify solute & solvent • Solute – changes phase, substance you have less of • Solvent Solven – substance you have the most of, maintains phase

Aqueous Solutions • Water is the solvent. • Transition metals form brightly colored solutions.

Soluble • Soluble – capable of being dissolved. • A 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 • Solubility = maximum amount of 1 substance that will dissolve in a given amount of another substance. • LIMITS to the amounts of most liquid or solid solutes that will dissolve in a given solvent. • Temperature and pressure can affect solubility.

Factors that affect the rate of dissolving • Rate of dissolving is different from the amount that will dissolve! • 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. • 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) Na. Cl(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 Na. Cl

Solvation • 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. • Solvent molecules may be polar or nonpolar.

Hydration • Specific name for the solventsolute interaction when the solvent is water.

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

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

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

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. )

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

Oil & H 2 O are immiscible.

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

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

Vocabulary Interlude • Electrolyte: Electrolyte A substance that dissolves in water to form a solution that conducts electricity. (There are ions in the solution. ) • Nonelectrolyte: Nonelectrolyte 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. • Concentrated – relatively large amounts of solute. • Dilute – 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? What can you say about the number of solute particles in pictures b and c? It’s the same!

Unsaturated Solution • Has 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. • Solubility = amount of solute required to form a saturated solution.

The solution is saturated when the solute stops dissolving.

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

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

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

3 possible results: Unsaturated solution. • No apparent change in crystal Saturated solution. • Crystal dissolves • Bam! Suddenly have lots of solid solute in beaker. 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 B C D D = dilute & unsaturated. 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.

Summary of Dissolving • Occurs at the surface of the solid. • Involves an interaction between the solute and the solvent. • Interaction is called “solvation. ” • If water is the solvent, the interaction is called “hydration. ” • 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 solids have a positive slope – the hotter the water, the more solute dissolves. • All gases have a negative slope – the hotter the water, the less gas dissolves. – The colder the water, the more gas dissolves.