Properties of Solutions Prentice-Hall Chapter 16.1 Dr. Yager

Objectives  Identify the factors that determine the rate at which a solute dissolves.  Identify the units usually used to express the solubility of a solute.  Identify the factors that determine the mass of solute that will dissolve in a given mass of solvent.

Solutions Solutions are homogeneous mixtures that may be solid, liquid, or gas. Solvent - the dissolving medium Solute - the dissolved particles Solute - the dissolved particles A solvent dissolves the solute and the solute is dissolved in a solvent.

Key Ideas The chemical compositions of the solvent and the solute determine whether a substance will dissolve. Stirring (agitation), temperature, and the surface area of the dissolving particles (solute) determine how fast the substance will dissolve.

Factors Affecting How Fast a Solution Will Form  Stirring (agitation) – fresh solvent in contact with surface of solute  Temperature – increased kinetic energy of the liquid means increased frequency and force of collisions  Particle size – smaller particles have more surface area per unit mass

A cube of sugar in cold tea dissolves slowly.

Granulated sugar dissolves in cold water more quickly than a sugar cube, especially with stirring.

Granulated sugar dissolves very quickly in hot tea.

Solubility: the amount of solute that dissolves in a given quantity of solvent at a specified temperature and pressure to produce a saturated solution. Saturated solution: a solution with the maximum amount of solute that can dissolve in a given quantity of solvent at a constant temperature and pressure. Solubility Means Saturated Solution!

Solvation of an Ionic Solid

What happens when a solution becomes saturated? Particles come off, or are solvated or dissolved, from the solid. Particles reattach, or crystallize, to the solid. Dissolving equals crystallizing, the amount of solute is constant. dynamic equilibrium!

Solubility is often expressed in grams of solute per 100 g of solvent. Example: 71 g/100 ml * of water for MgSO 4 71 g/100 ml * of water for MgSO 4 (Epsom Salt) (Epsom Salt) * density of water is 1 g/ml

 Some liquids combine in all proportions, while others don’t mix at all.  Two liquids are miscible if they dissolve in each other in all proportions (i.e. water and alcohol).  Two liquids are immiscible if they are insoluble in each other (i.e. water and oil).

Factors Affecting Solubility  Solubility is the amount of solute which will dissolve in a given amount of solvent.  Temperature affects the solubility of solid, liquid, and gaseous solutes in a solvent; both temperature and pressure affect the solubility of gaseous solutes.

Temperature  The solubility of most solid substances increases as the temperature of the solvent increases.  The solubility of most gases is greater in cold water than in hot water.

The mineral deposits around hot springs result from the cooling of the hot, saturated solution of minerals emerging from the spring.

 A supersaturated solution contains more solute than it can theoretically hold at a given temperature.  The crystallization of a supersaturated solution can be initiated if a very small crystal, called a seed crystal, of the solute is added.

A supersaturated solution is clear before a seed crystal is added.

Crystals begin to form in the solution immediately after the addition of a seed crystal.

Excess solute crystallizes rapidly.

Pressure  Changes in pressure have little effect on the solubility of solids and liquids, but pressure strongly influences the solubility of gases.  Gas solubility increases as the partial pressure of the gas above the solution increases.

Henry’s Law Henry’s law states that at a given temperature, the solubility (S) of a gas in a liquid is directly proportional to the pressure (P) of the gas above the liquid.

1. For a given substance, which of the following will NOT influence how fast it dissolves? a.temperature b.amount of agitation c.molar mass d.size of the crystals

1. For a given substance, which of the following will NOT influence how fast it dissolves? a.temperature b.amount of agitation c.molar mass d.size of the crystals

2. The solubility of a substance is often expressed as the number of grams of solute per a.100 liters of solvent. b.1 cm 3 of solvent. c.100 grams of solution. d.100 grams of solvent.

2. The solubility of a substance is often expressed as the number of grams of solute per a.100 liters of solvent. b.1 cm 3 of solvent. c.100 grams of solution. d.100 grams of solvent.

3. The solubility of a gas in a solvent is affected by a.both temperature and pressure. b.only pressure. c.only temperature. d.both pressure and agitation.

3. The solubility of a gas in a solvent is affected by a.both temperature and pressure. b.only pressure. c.only temperature. d.both pressure and agitation.