Answers to Questions & Problems in Textbook - Chapter 2

1. We can "see" atoms with a scanning tunneling microscope.
2. in your text
3. When we say that a compound always has the same composition, we mean that they molecules of that compound always contain the same type and same ratio of each type of atom.
4. in your text
5. The gaseous 10 g sample of water has a much larger volume than either the solid or liquid samples. While the 10-g sample of water vapor contains the same amount of water as the solid and liquid sample (the same mass and therefore the same number of water molecules), there is a great deal of empty space in between the molecules of the gaseous sample.
The solid state takes up a slightly larger volume than the liquid sample because when the liquid water molecules arrange into the solid ice crystal structure, there is some empty space in between the molecules. In Figure 2.7 on pg 31 in your text, compare picture (a) with picture (b)
6. in your text
7. physical
8. in your text
9. in your text
10. the substance reacts with iron(II) sulfate
11. Electrolysis is the passage of an electrical current through a substance of solution to force a chemical reaction to occur. Electrolysis causes chemical changes to take place that would ordinarily not take place on their own. When an electrical current is passed through water, the current causes the water molecules to break down into their constituent elements (hydrogen gas and oxygen gas).
12.
a. in your text The fiber of your shirt actually turn into new molecules when they scorch.
b. physical; the air in the tires decreases in volume with the temperature, but it is still air.
c. in your text
d. chemical; the oven cleaner contains sodium hydroxide which converts greases in the oven into soaps
e. Your text says this is chemical, which is true if by the term "leak" they mean, slowly discharge electricity. However, you are more likely think the term "leak" as refering to chemicals simply getting out of the package, then it is physical change.
f. chemical; the acids attack and react with the calcium phosphate matrix of the teeth
g. in your text
h. chemical; iron in the blood catalyzes the decomposition of the hydrogen peroxide into oxygen gas (and water)
i. in your text
j. chemical; chlorine is an oxidizing agent and can change the chemical nature of the dyes in the fabrics
13. heterogeneous mixtures: salad dressing, salad, m & m's, the change in your pocket
solutions (homogeneous mixtures): window cleaner, shampoo, rubbing alcohol, salt water, kool-aid, brass door knobs
14.
a. in your text
b. mixture
c. in your text
d. pure substance
15.
a. in your text
b. heterogeneous
c. in your text
d. homogeneous
e. the paper itself is basically homogeneous in appearacne
16. Consider a salt solution (sodium chloride in water). Since water boils at a much lower temperature than sodium chloride, the water can be boiled off from the solution, collected, and subsequently condensed back into the liquid state. This separates the two chemical substances.
A second example could be that a mixture of alcohol and water could be separated by distillation because they both will boil off, but at different temperatures. The alcohol would boil off first and then the water would boil off.
17. in your text
18. If water is added to the sample, and the sample is then heated to boiling, this should dissolve the benzoic acid but not the charcoal. The hot sample could then be filtered, which would remove the charcoal. The solution which passed through the filter could then be cooled, which should cause some of the benzoic acid to crystallize, or the solution could be heated carefully to boil off the water leaving benzoic acid behind.
19. in your text
20. in your text. Since two very different substances form at each electrode, there must be a chemical reaction occuring.
21. Chalk must be a compound, since it loses mass when heated, and appears to change into a substance with different physical properties (the hard chalk turns into a crumbly substance).
22. in your text
23. Liquids and gases are both fluid, that is to say they both flow freely and take on the shape of their container. At the nanoscopic level this is because the molecules in liquids are NOT stuck together. However, gases are compressible and liquids are incompressible. At this nanoscopic level this is because gas molecules are far apart from each other, yet liquid particles are relatively close together, "shoulder to shoulder" in fact.
24. in your text
25. physical
26. in your text