GROUP AND
    DISCUSSION
    ACTIVITIES    Key Questions
                                        1. Distinguish between the solute and the solvent in each solution in the laboratory
                                        and demonstration activities of this unit. [NOTE: The selection is arbitrary in some
                                        cases.]
                                        2. Why do colloidal particles remain dispersed throughout the solvent instead of falling
                                        to the bottom of the container? [See Content in a Nutshell.]
                                        3. Why is molarity (M) a convenient unit for solution reactions? [Solutions used in
                                        reactions are usually measured by volume. The stoichiometry of reactions is based on
                                        moles. Thus, moles of solute per liter of solution is the most convenient unit.]
                                        4. Why are so many different concentration units used? Consider the types of
                                        situations when each might be preferred. [Molarity is discussed in the answer to
                                        Question 3. Molality is useful for colligative property studies to keep the amount of
                                        liquid solvent constant; mole fraction is useful for colligative properties of gases; % by
                                        mass for components that are easily weighed; % mass to volume for solids in liquids;
                                        % by volume and volume:volume for liquids in liquids; and ppm for trace amounts of
                                        solids in liquid solvents.]
                                        5. Differentiate the properties that would allow the use of distillation for the separation
                                        of solution components from those that would allow the use of crystallization.
                                        [Distillation would be necessary if both components were liquids, whereas
                                        crystallization is satisfactory for solid components.]
                                        6. Why are the colligative properties of aqueous solutions affected more by a given
                                        number of moles of an electrolyte than by the same number of moles of a
                                        nonelectrolyte? [Colligative properties depend on the number of particles and
                                        electrolytes have more particles per mole as a result of ionization or dissociation.]
Counterintuitive Examples and Discrepant Events

1. When a dog urinates on grass, urea (a fertilizer) is added to the soil in high concentration. Why does the grass die? [The osmotic imbalance dehydrates the cells in the grass, and it dies.]
2. Deep-sea divers use helium/oxygen gas solutions rather than air for breathing because of the problem (the bends) that occurs when nitrogen is used. Why? [Because of the high solubility of nitrogen in water at higher pressures. Helium is much less soluble.]

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