Page 19 - Theory and Problems of BEGINNING CHEMISTRY

8 BASIC CONCEPTS [CHAP. 1

1.6. TNT is a compound of carbon, nitrogen, hydrogen, and oxygen. Carbon occurs is two common forms—
graphite (the material in “lead pencils”) and diamond. Oxygen and nitrogen comprise over 98% of the
atmosphere. Hydrogen is an element that reacts explosively with oxygen. Which of the properties of the
elements determines the properties of TNT?
Ans. The properties of the elements do not matter. The properties of the compound are quite independent of those
of the elements. A compound has its own distinctive set of properties. TNT is most noted for its explosiveness.

1.7. What properties of stainless steel make it more desirable for many purposes than ordinary steel?
Ans. Its resistance to rusting and corrosion.

1.8. What properties of DDT make it useful? What properties make it undesirable?

Ans. DDT’s toxicity to insects is its useful property; its toxicity to humans, birds, and other animals makes it
undesirable. It is stable, that is, nonbiodegradable (does not decompose spontaneously to simpler substances
in the environment). This property makes its use as an insecticide more difficult.

1.9. Name an object or an instrument that changes:

(a) chemical energy to heat (d ) electrical energy to light
(b) chemical energy to electrical energy (e) motion to electrical energy
(c) electrical energy to chemical energy (f ) electrical energy to motion

Ans. (a) gas stove (d ) lightbulb
(b) battery (e) generator or alternator
(c) rechargeable battery (f ) electric motor

1.10. A sample contains 88.8% oxygen and 11.2% hydrogen by mass, and is gaseous and explosive at room
temperature. (a) Is the sample a compound or a mixture? (b) After the sample explodes and cools, it is a
liquid. Is the sample now a compound or a mixture? (c) Would it be easier to change the percentage of
oxygen before or after the explosion?
Ans. (a) The sample is a mixture. (The compound of hydrogen and oxygen with this composition—water—is
a liquid under these conditions.)
(b) It is a compound.
(c) Before the explosion. It is easy to add hydrogen or oxygen to the gaseous mixture, but you cannot
change the composition of water.

1.11. Name one exception to the statement that nonmetals lie to the right of the stepped line in the periodic
table (page 350).
Ans. Hydrogen

1.12. Calculate the ratio of the number of metals to the number of nonmetals in the periodic table (page 350).
Ans. There are 109 elements whose symbols are presented, of which 22 are nonmetals and 87 are metals, so the
ratio is 3.95 metals per nonmetal.

1.13. Give the symbol for each of the following elements: (a) iron, (b) copper, (c) carbon, (d ) sodium, (e)
silver, (f ) aluminum.
Ans. (a)Fe (b)Cu (c)C (d)Na (e)Ag (f)Al

1.14. Name each of the following elements: (a)K,(b)P,(c) Cl, (d)H,(e)O.
Ans. (a) Potassium (b) Phosphorus (c) Chlorine (d ) Hydrogen (e) Oxygen