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Online
Introductory Chemistry
Answers to Self Test on Balancing Equations and Mass
Calculations
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Short
essay questions
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1.
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What are the
sources of repulsions and attractions in the hydrogen
molecule. Give answer in
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terms of nuclei and
valence electrons.
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The
illustration shows a "freeze frame" picture of the electrons
and protons in a
H2
molecule
at
a random instant. The positions are changing.
The
red lines indicate repulsions. The blue lines indicate
attractions
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Repulsions
result from interaction of one electron with the other
electron and the interaction
of one nucleus with
the other nucleus.
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Attractions
result from the interaction of the electrons with their own
nucleus and with the
nucleus in the other
atom.
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2.
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What is the origin
of the octet rule? Is it universally followed?
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If any exceptions
exist, what causes them?
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The
octet rule arises from the fact that the ns and np subshells
can hold only a maximum of
eight
electrons.
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The
row 2 elements cannot have more than 8 electrons in the
"2s2p" subshells. The octet
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rule
is usually followed by C, N, O , and F in row 2. They can
form a maximum of 4 bonds.
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The
elements in the other rows do not always follow the octet
rule.
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The
exceptions to the octet rule result when atoms can use "d"
subshells to form bonds.
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This
means an atom can form 5, 6 or 7 bonds using (n-1)d ns np
subshells.
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3.
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Give the names for
the following compounds.
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HCl,
PCl5,
NO2,
Cl2O5,
CO, CO2,
N2O4,
SO3
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HCl,
hydrogen chloride. This is the pure
compound and should not be confused with
theaqueous
solution that is HCl(aq) hydrochloric acid.
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PCl5,
phosphorus pentachloride
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NO2,
nitrogen dioxide
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Cl2O5,
dichlorine pentoxide
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CO,
carbon monoxide
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CO2,
carbon dioxide
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N2O4
, dinitrogen
tetroxide
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SO3,
sulfur trioxide
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What does the term
binary compound mean?
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A
binary compound is any compound made up of two elements like
HBr,
Cl2O5,
N2O4
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4.
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Draw the Lewis dot
formula for HNO3. Identify
the central atom and any multiple bonds.
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What is the shape
around the central atom in
HNO3? give bond angles
The
shape around the nitrogen central atom is planar triangular
or trigonal planar. These are
the same. The bond
angles are close to 120o.
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Indicate the
polarity of bonds using +---> arrows .
The electrons shift toward the oxygen
end of the N-O and H-O
bonds. This is true in all bonds involving oxygen.
(Exception O-F )
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1.
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Which of the
following pairs of atoms will form a single covalent
bond.
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a. Na and Cl This
pair forms an ionic bond
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b. He and He These
two rare gas forms no bond
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c. Ne and He This
pair of rare gases forms no bondsforms no bond
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d.
H and O hydrogen can
only form a single bond
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2.
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Which of the
following molecules contains exactly 24 valence
electrons?
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a. NO
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b.
NO2
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c.
CO2
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d.
SO3
Sulfur
has 6 valence, each oxygen has
6 valence electrons. 1 x 6 + 3 x 6 = 24
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3.
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Which of the
following pairs of atoms can form a double bond?
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a. He and He
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b. H and H
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c. N and H
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d.
N and O
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4.
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Which of the
following atoms can form a double bond?
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a. C
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b. O
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c. N
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d.
all of
these
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5.
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Which of the
following pairs of names and symbols is incorrect?
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a.
silicon tetrafluoride,
SiF
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b. nitrogen
dioxide, NO2
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c. phosphorus
trichloride, PCl3
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d. phosphorus
pentachloride, PCl5
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6.
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Which of the
following sets of elements normally exists as diatomic
molecules?
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a. nitrogen, neon,
helium, oxygen
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b.
nitrogen, oxygen,
chlorine, fluorine
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c. helium, neon,
argon
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d. sodium, calcium,
zinc
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7.
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Which of the
following molecules is the most polar?
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a.
hydrogen chloride,
HCl
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b. hydrogen iodide,
HI
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c. hydrogen,
H2
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d. chlorine,
Cl2
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8.
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Which of the
following molecules contains a multiple bond?
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a. methane,
CH4
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b.
nitrogen,
N2
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c. hydrogen,
H2
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d. chlorine,
Cl2
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9.
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The smallest
possible unit of a covalent compound is usually considered
to be a(an)
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a. atom
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b. cation
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c.
molecule
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d. polyatomic
ion
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10.
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The systematic name
for ICl3
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a.
iodine
trichloride
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b. iodine
trichlorine
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c. iridium
trichloride
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d.
triiodinechloride
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11.
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A double bond
exists when two atoms share ______ electrons.
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a. two
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b. three
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c.
four
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d. six
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12.
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Carbon dioxide is a
linear molecule. The electronegativity of carbon is 2.5. The
electronegativity
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of oxygen is 3.5.
The bond between C and O is considered to be
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a. nonpolar
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b.
polar
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c. ionic
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d. weak
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13.
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Water molecules are
polar. This is only possible if the molecule
is_________________
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a. linear
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b. tetrahedral
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c.
bent
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d. pyramidal
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14.
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What is the
predicted shape the carbon tetrachloride molecule
CCl4
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a. linear
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b. trigonal
planar
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c. pyramidal
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d.
tetrahedral
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15.
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Which of the
following does not obey the octet rule?
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a. phosphorus
pentachloride
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b. nitrogen
monoxide
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c. sulfur
hexafluoride
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d.
all of
these
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16.
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Carbon in the Lewis
dot formula for carbonate ion has _____ single bond(s)
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and _____multiple
bond(s).
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a.
two ......
one
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b. two ......
two
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c. one ......
none
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d. four ......
two
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