Download Answers to End-of-Chapter Questions – Brooker et al ARIS site

Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 2
Test Yourself Questions
1. _____________________ make up the nucleus of an atom.
a. Protons and electrons
b. Protons and neutrons
c. DNA and RNA
d. Neutrons and electrons
e. DNA only
Answer: b. Protons and neutrons are found at the center of the atom, the atomic nucleus.
2. Living organisms are composed mainly of
a. calcium, hydrogen, nitrogen and oxygen.
b. carbon, hydrogen, nitrogen and oxygen.
c. hydrogen, nitrogen, oxygen, and helium.
d. carbon, helium, nitrogen, and oxygen.
e. carbon, calcium, hydrogen and oxygen.
Answer: b. About 95% of the atoms in most organisms are carbon, hydrogen, nitrogen and oxygen.
3. The ability of an atom to attract bonded electrons is
a. polarity.
b. electronegativity.
c. solubility.
d. valence.
e. both a and b.
Answer: b. Electronegativity is a measure of an atom’s ability to attract electrons.
4. Hydrogen bonds differ from covalent bonds in that
a. covalent bonds can form between any type of atom and hydrogen bonds only form between
H and O.
b. covalent bonds involve sharing of electrons and hydrogen bonds involve the complete
transfer of electrons.
c. covalent bonds result from equal sharing of electrons but hydrogen bonds involve unequal
sharing of electrons.
d. covalent bonds involve sharing of electrons between atoms but hydrogen bonds are the
result of weak attractions between a hydrogen atom of a polar molecule and an electronegative
atom of another polar molecule.
e. covalent bonds are weak bonds that break easily but hydrogen bonds are strong links
between atoms that are not easily broken.
Answer: d. Covalent bonds are formed when atoms share electrons. Hydrogen bonds, however, are
electrostatic attractions between hydrogen atoms of a polar molecule and an electronegative atom of
another polar molecule.
5. A free radical
a. is a positively charged ion.
b. is an atom with one unpaired electron in its outer shell.
c. is a stable atom that is not bonded to another atom.
d. can cause considerable cellular damage.
e. both b and d.
Answer: e. A free radical, a highly unstable atom with a single unpaired electron in its outer shell, can
cause extensive damage to cells.
6. Chemical reactions in living organisms
a. require energy to begin.
b. usually require a catalyst to initiate the process.
c. are usually reversible.
d. occur in liquid environments, such as water.
e. all of the above.
Answer: e. Chemical reactions require energy, are usually catalyzed by enzymes, are reversible, and
take place in aqueous solutions.
7. Solutes that easily dissolve in water are said to be
a. hydrophobic.
b. hydrophilic.
c. polar molecules.
d. all of the above.
e. b and c only.
Answer: e. Water-soluble substances are usually polar molecules and said to be hydrophilic.
8. The sum of the atomic masses of all the atoms of a molecule is its
a. atomic weight.
b. molarity.
c. molecular mass.
d. concentration.
e. polarity.
Answer: c. The molecular mass is the sum of the atomic masses of all the atoms of a particular
molecule.
9. Reactions that involve water in the breaking apart of other molecules are known as __________
reactions.
a. hydrophilic
b. hydrophobic
c. dehydration
d. anabolic
e. hydrolytic
Answer: e. Reactions that utilize water to break apart other molecules are called hydrolytic reactions.
10. A difference between a strong acid and a weak acid is
a. strong acids have a higher molecular mass than weak acids.
b. strong acids completely ionize in solution, but weak acids do not completely ionize in solution.
c. strong acids give off two hydrogen ions per molecule, but weak acids only give off one
hydrogen ion per molecule.
d. strong acids are water soluble, but weak acids are not.
e. strong acids give off hydrogen ions and weak acids give off hydroxyl groups.
Answer: b. The differences between strong acids and weak acids is the degree to which they ionize in
solution. Strong acids completely ionize in solution, but weak acids only partially ionize in solution.
Conceptual Questions
1. What are the three types of chemical bonds commonly found in biological molecules?
Answer: Covalent bonds are bonds in which atoms share electrons. A hydrogen bond is a weak polar
covalent bond that forms when a hydrogen atom from one polar molecule becomes electrically attracted
to an electronegative atom. The strong attraction between two oppositely charged forms an ionic bond.
2. Distinguish between hydrophobic and hydrophilic.
Hydrophobic: “Water-fearing”—molecules that are not attracted to water molecules. Hydrophilic:
“Water-loving”—generally, ions and molecules that contain polar covalent bonds will dissolve in water and are
said to be hydrophilic.
3. List the special properties of water that are ideally suited to life.
Answer: Examples include high heat of vaporization, high heat of fusion, colligative properties, versatility
as a solvent and surface tension. Also see Figure 2.20.
Experimental Questions
1. Before the experiment conducted by Ernest Rutherford, how did many scientists envision the
structure of an atom?
Answer: Scientists were aware that atoms contained charged particles. Many believed that the positive
charges and mass were evenly distributed throughout the atom.
2. What was the hypothesis tested by Rutherford?
Answer: Rutherford was testing the hypothesis that atoms are composed of positive charges evenly
distributed throughout the atom. Based on this model of the structure of the atom, alpha particles,
positively charged atoms, should pass through the foil, often times showing a small level of deflection
due to the presence of positive charges in the gold foil.
3. What were the results of the experiment? How did Rutherford interpret the results of his experiment?
Answer: Instead of detecting slight deflection of most alpha particles as they passed through the gold
foil, the majority, 98%, of the alpha particles passed directly through the gold foil. A much smaller
percentage either deflected or bounced back from the gold foil. Rutherford suggested that since most of
the alpha particles passed directly through the gold foil, most of the volume of atoms is empty space.
Rutherford also proposed that the bouncing back of some of the alpha particles indicated that most of
the positively charged particles were concentrated in a compact area. These results were counter to the
hypothesized model.
Collaborative Questions
1. Discuss the three basic subatomic particles.
Answer:
Protons - These are positively charged particles that are found in the center of the atom which is also
referred to as the nucleus. The number of protons an atom has is called the atomic number and this
defines each type of element. This particle also has mass and makes up approximately half of the mass
of an atom which is referred to as the atomic mass.
Neutrons - These are neutral particles that are found in the center of the atom. For most atoms, the
number of neutrons is equal to the number of protons in an atom but this is not always the case. Atoms
with the same number of protons but different numbers of neutrons are called isotopes of each other.
Electrons - These are negatively charged particles that are found in orbitals around the nucleus. For
atoms, the number of protons is equal to the number of electrons. Therefore the overall charge of the
atom is neutral. If electrons are added to an atom or taken away this will change the charge of the atom,
which is now called an ion, thereby changing its properties and reactivity.
2. Discuss several properties of water that make it possible for life to exist.
Answer:
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Water is a solvent for many kinds of polar and ionic substances.
Water can directly participate in types of chemical reactions called hydrolytic reactions.
Water has a high heat of vaporization and takes a great deal of heat to go from a liquid to a gas. As
a result of this most of the water in our planet is in liquid form which is needed to support life.
Water also has a high heat of fusion and requires a great deal of energy to be removed from it to
turn it from a liquid to a solid. As a result of this water is very stable and it is resistant to temperature
change which is good for living organisms.
Also see Figure 2.20.