Chapter 9

Relate the terms solute, solvent, and solution in a sentence.

Solutes are dissolved in a solvent to make a solution. (p. 204)

Classify the following as heterogeneous or homogeneous:

salt water

homogeneous

Classify the following as heterogeneous or homogeneous:

smog

heterogeneous

Classify the following as heterogeneous or homogeneous:

chalk in water

heterogeneous

Classify the following as heterogeneous or homogeneous:

brass alloy

homogeneous

During the dissolving process, the solute becomes solvated. Explain.

The solute particles are surrounded by solvent particles.

Would a mixture of a liquid with a solid with particle size 2 μm be considered a suspension, colloid, or solution? Explain.

The cutoff between a colloid and a suspension is 1 µm; therefore, this would be considered a suspension.

Dissolving sodium hydroxide (NaOH) is a highly exothermic process. Where does this energy come from?

As solute is dissolved, the solute particles have to be separated from each other and the solvent particles have to be separated from each other. Both processes are endothermic. The process of the solute and solvent particles attracting each other is exothermic. When dissolving NaOH, the energy released in the third process must be significantly higher than the energy needed for the first two.

Why does the definition of solubility include the temperature?

Solubility changes with temperature; therefore, a solubility value is valid only at a particular temperature.

Why does a warm soda fizz more than a cold soda?

The solubility of a gas dissolved in a liquid decreases as temperature increases. At high temperatures, less of the gas can stay in solution.

What does “like dissolves like” mean?

For solutions generally, polar solvents will dissolve polar solutes and nonpolar solvents will dissolve nonpolar solutes. So if the polar nature of the solute and solvent are alike, the solute will typically be soluble.

Why do people add sugar to the tea while it is hot when making sweetened ice tea?

The dissolving process will occur faster and more sugar can be dissolved.

Which method would work to separate

a. iron filings from sand?

magnetism

Which method would separate:

pollen from the air?

filtration

Which method would separate:

table salt from water?

distillation or evaporation

According to the graph, what is the solubility of NaNO3 in 100 g of water at 50°C?

approximately 115 g (p. 208) SEE BOOK TO SEE WHY

According to the graph, what happens to the solubility of NH3 as the temperature increases?

The solubility of NH3 decreases with increased temperature.

What is a dilute solution?

is one that has a relatively small amount of solute particles dissolved in it.

Explain how to calculate percent by mass.

divide the mass of the solute by the total mass of the solution (solute plus solvent) and then multiply by 100%

Define molarity.

a measure of concentration that indicates the moles of solute in 1 L of solution.

Why does the boiling point of a solution rise as solute is added?

As solute is added, the vapor pressure is lowered. Therefore, the temperature to raise the liquid’s vapor pressure to its boiling point must be increased.