Unit 11 - Solutions and Colligative Properties

Introduction:

Unit 11 (Chapters 12-13) gets away from gases and moves towards the study of mixtures and solutions. We briefly touched upon these much earlier in the year, but now we will take a look at them much more in-depth. Topics covered in this chapter will include the various types of mixtures, colloids, Brownian motion, concentration, solvation and colligative properties.

Student Objectives - Unit 11:

11.1

a. Solutions are homogeneous mixtures.

b. Mixtures are classified as solutions, suspensions or colloids, depending on the size of the solute particles in the mixture.

c. The dissolved substance is the solute. Solutions that have water as a solvent are aqueous solutions.

d. Solutions can consist of solutes and solvents that are solids, liquids or gases.

e. Suspensions settle out upon standing. Colloids do not settle out, and they scatter light that is shined through them.

f. Most ionic solutes and some molecular solutes form aqueous solutions that conduct an electric current. These solutes are called electrolytes.

g. Nonelectrolytes are solutes that dissolve in water to form solutions that do not conduct.

11.2

a. A solute dissolves at a rate that depends on the surface area of the solute, how vigorously the solution is mixed, and the temperature of the solvent.

b. The solubility of a substance indicates how much of that substance will dissolve in a specific amount of solvent under certain conditions.

c. The solubility of a substance depends on the temperature.

d. The solubility of gases in liquids increases with increases in pressure.

e. The overall energy absorbed as heat by the system when a specific amount of solute dissolved during solution formation is called the enthalpy of solution.

11.3

a. Two useful expressions of concentration are molarity and molality.

b. The molar concentration of a solution represents the ratio of moles of solute to liters of solution.

c. The molal concentration of a solution represents the ratio of moles of solute to kilograms of solvent.

12.1

a. The separation of ions that occurs when an ionic solid dissolves is called dissociation.

b. When two different ionic solutions are mixed, a precipitate may form if ions from the two solutions react to form an insoluble compound.

c. A net ionic equation for a reaction in aqueous solution includes only compounds and ions that change chemically in the reaction. Spectator ions are ions that do not take part in such a reaction.

d. Formation of ions from molecular compounds is called ionization. A molecular compound may ionize in an aqueous solution if the attraction of the polar water molecules is strong enough to break the polar-covalent bonds of the solute molecules.

e. An H₃O⁺ ion is called a hydronium ion.

f. All, or almost all, of a dissolved strong electrolyte exists as ions in an aqueous solution, whereas a relatively small amount of a dissolved weak electrolyte exists as ions in an aqueous solution.

12.2

a. Colligative properties of solutions depend only on the total number of solute particles present. Boiling point elevation, freezing point depression, vapor pressure lowering and osmotic pressure are colligative properties.

b. The molal boiling point and freezing point constants are used to calculate boiling point elevations and freezing point depressions of solvents containing nonvolatile solutes.

c. Electrolytes have a greater effect on the freezing and boiling points of solvents than nonelectrolytes do.

d. Except in very dilute solutions, the values of colligative properties of electrolyte solutions are less than expected because of the attraction between ions in solution.

Ohio Department of Education - Chemistry Standards:

There are no standards directly related to this chapter. However, this chapter will provide framework for learning acid-base chemistry and for anyone who will be taking college chemistry in the future.

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