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ANSWERS TO SAMPLE QUESTIONS FOR THE
CHEMISTRY PLACEMENT EXAM
| 1. |
Aluminum reacts with element X
to form a compound with the formula Al2X3. Element X
exists as diatomic molecules, X2, in the gaseous state at normal
temperature and pressure. Element X must be |
| a) |
Nitrogen |
| X) |
Oxygen |
| c) |
Sulfur |
| d) |
Chlorine |
Aluminum forms a +3 ion. In order for the formula unit Al2X3
to be electrically neutral, the element X must form a -2 ion. Nonmetals in the
oxygen column do this. Of these elements, only oxygen is a diatomic gas.
| 2. |
What is the coefficient of O2
when the following equation is balanced? C2H4O + O2 ® CO2 + H2O |
| a) |
2 |
| b) |
3 |
| c) |
4 |
| X) |
5 |
The balanced equation is 2 C2H4O + 5 O2 ® 4 CO2 + 4 H2O
| 3. |
How many moles of GeH4
are needed to form 8.00 moles of GeF3H according to the following
reaction? GeH4 + 3 GeF4 ®
4 GeF3H |
| X) |
2.00 |
| b) |
4.00 |
| c) |
8.00 |
| d) |
16.00 |
8.00 mol GeF3H ( 1 mol GeH4/ 4 mol GeF3H) =
2.00 mol GeH4
| 4. |
According to its location in the
periodic table, the element bromine ( element # 35) is best described as
|
| a) |
A metal |
| X) |
A nonmetal |
| c) |
A transition metal |
| d) |
A metalloid |
Nonmetals are toward the upper right of the periodic table. All the elements
in the fluorine column are nonmetals
| 5. |
Which of the following ions will
have the smallest ionic radius? |
| a) |
S- |
| b) |
Cl
2-
|
| c) |
K+ |
| X) |
Ca2+ |
These ions all have 20 electrons. Since they all have the same number of
electrons, the size depends on the magnitude of the positive nuclear charge.
Calcium has the largest nuclear charge (+20) so its nucleus attracts the
electrons most strongly, and it is the smallest of these ions.
| 6. |
Which of the following molecules
has trigonal planar geometry? |
| X) |
BF3 |
| b) |
NH3 |
| c) |
PCl3 |
| d) |
IF3 |
In the Lewis dot structure of BF3, there are no lone pairs of
electrons around the boron atom. According to VSEPR theory, this results in
perfect triangular geometry, which is called trigonal planar. The other species
all have at least one lone pair on the central atom, which distorts the
geometry. NH3 and PCl3 have one lone pair, and are
trigonal pyramidal. IF3 has two lone pairs, and is T-shaped.
| 7. |
Which of the following species
is neither acidic nor basic when dissolved in water? |
| a) |
HCl |
| b) |
NH3 |
| X) |
NaCl |
| d) |
NaHCO3 |
HCl, hydrochloric acid, is a strong acid. NH3, ammonia, is a weak
base. In a solution of NaHCO3, sodium hydrogen carbonate (baking
soda), the hydrogen carbonate ion, HCO3-
,
acts as a base. Neither the sodium ion Na+, nor the chloride ion, Cl - , which form when NaCl is dissolved in water, has
significant acidic or basic properties.
| 8. |
What will be the effect on the
following equilibrium if the pressure is increased by decreasing the volume
of the reaction vessel? H2(g) + I2(g) = 2 HI (g)
|
| a) |
The equilibrium will shift to
the right. |
| b) |
The equilibrium will shift to
the left. |
| X) |
The equilibrium will not shift. |
| d) |
The effect cannot be predicted. |
According to LeChatelier's principle, an equilibrium will shift to offset the
results of an applied stress. If the pressure increases, an equilibrium will, if
possible, shift in such a way as to decrease the pressure. In this case,
however, there are equal numbers of gas molecules on both sides of the equation,
so the equilibrium cannot relieve the increased pressure, and will therefore not
shift.
| 9. |
To the correct number of
significant figures, the result of the following calculation
[(11.13 - 2.6) x 104]/[103.15 x 10-
6]
should be reported as |
| a) |
8.27 x 108 |
| b) |
8.3 x 10-4 |
| X) |
8.3 x 108 |
| d) |
8.27 x 10-8 |
The "calculator answer" is 8.2695…. x 108. When the numbers in the
numerator are subtracted the result, 8.53, must be rounded to one decimal place,
or 8.5. Since this number has two significant figures, the result when it is
divided by a number with 5 significant figures is limited to two significant
figures.
| 10. |
Jack three times as old as Jim.
In four years, Jack will be twice as old as Jim. How old is Jim? |
| X) |
4 years old |
| b) |
8 years old |
| c) |
12 years old |
| d) |
16 years old |
Let x = Jack's age and y = Jim's age. Then, x = 3y and x + 4 = 2(y + 4). The
solution is x = 12, y = 4.
RETURN TO
PLACEMENT EXAM POLICY
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