CHAPTER 15 and 16 SOLUTIONS

Properties of Solutions OBJECTIVES: Identify the factors that determine the rate at which a solute dissolves.

Properties of Solutions OBJECTIVES: Identify the units usually used to express the solubility of a solute.

Properties of Solutions OBJECTIVES: Identify the factors that determine the mass of solute that will dissolve in a given mass of solvent.

THE NATURE OF SOLUTIONS A solution is a homogeneous mixture of 2 or more substances in a single physical state. Solute: A substance that is dissolved Solvent: The substance that does the dissolving (usually a liquid)

How Much? Solubility- is the maximum amount of substance that will dissolve at a specific temperature Saturated solution- Contains the maximum amount of solute dissolved.

How Much? Unsaturated solution- Can still dissolve more solute Supersaturated- solution that is holding more than it theoretically can;

Saturation and Equilibrium Saturation equilibrium established Solute is dissolving More solute is dissolving, but some is crystallizing

Types of Solutions Gas-Gas Gas-Liquid Liquid-Liquid Solid-Liquid Gas-Solid Liquid-Solid Solid-Solid Air (O2 and N2) Seltzer (CO2 and H2O) Antifreeze Ocean Water Charcoal Filter Dental Fillings Sterling Silver

Types of Solutions

Properties of Solutions A substance that dissolves in another substance is said to be Soluble. Examples: Salt and Sugar A substance that DOES NOT dissolve in another is said to be Insoluble. Examples: Nail, rock, wood Typically the solute is smaller / less than the solvent.

Solid Solutions Typically Alloys…..such as: Babbit (ball bearings) Bell Metal (Bells) Bronze (Coins) 18K gold (Jewelry) Sterling Silver (Flatware) Steel (Construction)

Aqueous Solutions Solutions with water as the solvent Water can dissolve many things because of its polarity and neutrality. Water is known as the universal solvent.

Liquid Solutions Miscible: ability of a liquid to form a solution with another liquid in all proportions. (water and milk) Immiscible: Inability of a liquid to form a solution. (oil and water)

Section 15.2 Concentration of Solutions OBJECTIVES: Solve problems involving the Molarity of a solution.

Section 15.2 Concentration of Solutions OBJECTIVES: Describe the effect of dilution on the total moles of solute in solution.

Concentration is... a measure of the amount of solute dissolved in a given quantity of solvent A concentrated solution has a large amount of solute A dilute solution has a small amount of solute These are qualitative descriptions But, there are ways to express solution concentration quantitatively

Concentrated vs. Dilute

Molarity Molarity = moles of solute liters of solution Abbreviated with a capital M, such as 6.0 M This is the most widely used concentration unit used in chemistry.

molality molality: is a measure of the number of MOLES of solute in 1 KILOGRAM solvent. m = mol solute / Kg solvent

Saturation Saturated: A solution is saturated if it contains as much solute as can possibly be dissolved under the existing conditions of temperature and pressure. Unsaturated: A solution that has less than the maximum amount of solute that can be dissolved is unsaturated.

Supersaturated: A solution that contains a greater amount of solute than that needed to form a saturated solution.

Exothermic and Endothermic Reactions Exothermic Reactions : Gives off heat (heat pack) Endothermic Reactions : Absorbs heat (cold pack)

Factors that affect solubility 1. Nature of Solute and Solvent 2. Temperature : As temperature increases, the kinetic energy becomes greater, thus solubility increases. 3. Pressure (gases) : As pressure increases, the kinetic energy becomes greater, thus the solubility increases.

Polar vs. Nonpolar Substances Polar Molecules : Based on molecular geometry : If there are unshared pairs of electrons on the central atom, then POLAR (Water, CH3Cl) Nonpolar compounds : Symmetrical compound : Same element on all sides : (oil, grease, soap, Cl2, CH4)

Examples of polar and nonpolar substances Water Alcohols Acetone Acetic Acid Formic Acid NonPolar Hexane Octane Carbon Tetrachloride Greases, petroleum oils, vege. oils Waxes, tars, gasoline

Like Dissolves Like Rule Solute Polar Solvent Nonpolar Solvent Polar Soluble Insoluble Nonpolar Ionic

Factors Affecting the Rate of Dissolving Surface Area : The dissolving of a solid solute takes place on the surface of the solid. : Solvent particles pull particles from the surface of the solute into solution. : Because dissolving occurs at the surface of the solute, it can be speeded up by increasing the surface area. : Crushing and grinding : Sugar cubes vs. sugar granulars vs. powdered sugar

Stirring : Speeds up the dissolving process because it increases the contacts between the solute and the solvent. Temperature : Increasing temperature increases the speed of the molecules of the solvent. : Faster solvent molecules means more contacts with the solute particles and thus a faster dissolving rate.

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Solids tend to dissolve best when: Heated Stirred Ground into smaller particles Gases tend to dissolve best when: The solution is cold Pressure is high