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3. Analyze the basic reason that water is a universal solvent, INVITATION TO INQUIRY
becomes less dense when it freezes, has a high heat of fusion, has
a high specific heat, and has a high heat of vaporization.
Water Temperature and Dissolving Gas
4. What is the same and what is different between a salt that will
What relationship exists, if any, between the temperature of water and
dissolve in water and one that is insoluble?
how much gas will dissolve in the water? You can find out by experi-
5. There are at least three ways to change the boiling point of water.
menting with water temperature and Alka-Seltzer tablets. Set up a flask
So describe how you know for sure that 100°C (212°F) is the
boiling point? on a sensitive balance, with two tablets wrapped in a tissue and lodged
in the neck of the flask. Record the weight, and then gently push the
6. What are the significant similarities and differences between an
acid, a base, and a salt? tissue so it falls into the water. The difference in mass will be a result of
carbon dioxide leaving the flask. Compare how much carbon dioxide
7. Describe how you would teach someone why the pH of an acid is
a low number (less than 7), while the pH of a base is a larger is dissolved in water of different temperatures. Should you expect the
number (greater than 7). same dissolving rate for oxygen?
8. Describe at least four different examples of how you could make
hard water soft.

PARALLEL EXERCISES

The exercises in groups A and B cover the same concepts. Solutions to group A exercises are located in appendix E.

Group A Group B
1. A 50.0 g sample of a saline solution contains 1.75 g NaCl. What 1. What is the percent by weight of a solution containing 2.19 g
is the percentage by weight concentration? NaCl in 75 g of the solution?
2. A student attempts to prepare a 3.50 percent by weight saline 2. What is the percent by weight of a solution prepared by
solution by dissolving 3.50 g NaCl in 100 g of water. Since dissolving 10 g of NaCl in 100 g of H 2 O?
equation 11.2 calls for 100 g of solution, the correct amount of
solvent should have been 96.5 g water (100 − 3.5 = 96.5). What
percent by weight solution did the student actually prepare?
3. Seawater contains 30,113 ppm by weight dissolved sodium and 3. A concentration of 0.5 ppm by volume SO 2 in air is harmful to
chlorine ions. What is the percent by weight concentration of plant life. What is the percent by volume of this concentration?
sodium chloride in seawater?
4. What is the mass of hydrogen peroxide, H 2 O 2 , in 250 grams of a 4. What is the volume of water in a 500 mL bottle of rubbing
3.0 percent by weight solution? alcohol that has a concentration of 70 percent by volume?
5. How many mL of pure alcohol are in a 200 mL glass of wine that 5. If a definition of intoxication is an alcohol concentration of
is 12 percent alcohol by volume? 0.05 percent by volume in blood, how much alcohol would be
present in the average (155 lb) person’s 6,300 mL of blood if that
person were intoxicated?
6. How many mL of pure alcohol are in a single cocktail made with 6. How much pure alcohol is in a 355 mL bottle of a “wine cooler”
50 mL of 40 percent vodka? (Note: “Proof” is twice the percent, that is 5.0 percent alcohol by volume?
so 80 proof is 40 percent.)
7. Fish in a certain lake are reported to contain 5 ppm by 7. In the 1970s, when lead was widely used in “ethyl” gasoline, the
weight DDT. (a) What percentage of the fish meat is DDT? blood level of the average American contained 0.25 ppm lead.
(b) How much of this fish would have to be consumed to reach The danger level of lead poisoning is 0.80 ppm. (a) What percent
a poisoning accumulation of 17.0 g of DDT? of the average person was lead? (b) How much lead would be in
an average 80 kg person? (c) How much more lead would the
average person need to accumulate to reach the danger level?
8. For each of the following reactants, draw a circle around the 8. Draw a circle around the proton donor and a box around the
proton donor and a box around the proton acceptor. Label which proton acceptor for each of the reactants, and label which acts as
acts as an acid and which acts as a base. an acid and which acts as a base.
+ – + –
(a) HC 2 H 3 O 2 (aq) + H 2 O(l) → H 3 O (aq) + C 2 H 3 O 2 (aq) (a) H 3 PO 4 (aq) + H 2 O(l) → H 3 O (aq) + H 2 PO 4 (aq)
+ – + –
(b) C 6 H 6 NH 2 (l) + H 2 O(l) → C 6 H 6 NH 3 (aq) + OH (aq) (b) N 2 H 4 (l) + H 2 O(l) → N 2 H 5 (aq) + OH (aq)
+ – + –
(c) HClO 4 (aq) + HC 2 H 3 O 2 (aq) → H 2 C 2 H 3 O 2 (aq) + ClO 4 (aq) (c) HNO 3 (aq) + HC 2 H 3 O 2 (aq) → H 2 C 2 H 3 O 2 (aq) + NO 3 (aq)
+ – + 2+ +
(d) H 2 O(l) + H 2 O(l) → H 3 O (aq) + OH (aq) (d) 2 NH 4 (aq) + Mg(s) → Mg (aq) + 2 NH 3 (aq) + H 2 ( g)

11-23 CHAPTER 11 Water and Solutions 297