Chemistry 161, North Seattle Community College
Abdi M.
Sample Practice Exam
For the multiple-choice questions, I would recommend you work on scratch paper and
circle the correct answer. There is only one correct choice. Make sure to balances all
chemical equations before you work on them.
1. Potassium dichromate, K2Cr2O7, is used in tanning leather, decorating porcelain and
water proofing fabrics. Calculate the number of chromium atoms in 78.82 g of
K2Cr2O7.
a. 9.490  1025 Cr atoms
b. 2.248  1024 Cr atoms
c. 1.124  1024 Cr atoms
d. 3.227  1023 Cr atoms
e. 1.613  1023 Cr atoms
2. Alkanes are compounds of carbon and hydrogen with the general formula CnH2n+2.
An alkane component of gasoline has a molar mass of between 125 and 130 g/mol.
What is the value of n for this alkane?
a. 4
b. 9
c. 10
d. 13
e. 14
3. Terephthalic acid, used in the production of polyester fibers and films, is composed of
carbon, hydrogen, and oxygen. When 0.6943 g of terephthalic acid was subjected to
combustion analysis it produced 1.471 g CO2 and 0.226 g H2O. If its molar mass is
between 158 and 167 g/mol, what is its molecular formula?
a. C4H6O7
b. C6H8O5
c. C7H12O4
d. C4H3O2
e. C8H6O4
4. Ammonia, an important source of fixed nitrogen that can be metabolized by plants, is
produced using the Haber process in which nitrogen and hydrogen combine.
N2(g) + H2(g)  NH3(g)
How many grams of nitrogen are needed to produce 325 grams of ammonia?
a. 1070 g
b. 535 g
c. 267 g
d. 178 g
e. 108 g
Chemistry 161, North Seattle Community College
Abdi M.
5. Aluminum metal reacts with chlorine gas to form solid aluminum trichloride, AlCl3.
What mass of chlorine gas is needed to react completely with 163 g of aluminum?
a. 214 g
b. 245 g
c. 321 g
d. 489 g
e. 643 g
Problem-Solving and Conceptual Section
6. As I have said in class, when sensors in car detect collision they cause the reaction of
sodium azide (NaN3) and generate nitrogen gas to fill the air bags within 0.03
seconds. The other product of the decomposition reaction of the sodium azide is solid
sodium. How many moles of nitrogen gas are produced if the airbag contains 132g
NaN3?
7. Magnesium (used in the manufacture of light alloys) reacts with iron (III) chloride to
form magnesium chloride and iron. A mixture of 41.0 g of magnesium (м = 24.31
g/mol) and 175 g of iron (III) chloride (м = 162.2 g/mol) is allowed to react. Identify
the limiting reactant and determine the mass of the excess reactant present in the
vessel when the reaction is complete.
Chemistry 161, North Seattle Community College
Abdi M.
8. Methanol (CH4O) is converted to bromomethane (CH3Br) by reacting it with
hydrogen bromide. The other product formed in this reaction in addition to
bromomethane is water. If 12.23 g of bromomethane are produced when 5.00 g of
methanol is reacted with excess HBr, what is the percentage yield?
9. Nitric acid is produced commercially by the Ostwald process. The three steps of the
Ostwald process are shown in the following equations.
4 NH3(g) + 5 O2(g)  4 NO(g) + 6 H2O(g)
2 NO(g) + O2(g)  2 NO2(g)
3 NO2(g) + H2O(l)  2 HNO3(aq) + NO(g)
What mass of NH3 must be used to produce 2.70 x106 kg HNO3 by the Ostwald
process, assuming 100% yield in each reaction?
Chemistry 161, North Seattle Community College
Conceptual Problems.
10. Fill in the empty boxes.
11. Follow the directions for each part in this question.
Abdi M.
Chemistry 161, North Seattle Community College
Abdi M.
Answer Key
1. D
2. B
3. E
4. C
5. E
6. 3.05 moles of N2 gas
7. Limiting reactant is FeCl3; 2.1 g of MgCl2 remain
8. 82.6 %
9. 1.09 x 106 kg
10.
1.26g/cm3
11.9 g
3.12 g/dm3
11. D. The diagram shows one element of X reacting with 2 elements of Y to form a 3
molecules of XY2. However, X is the limiting reactant and leaves 2 moles of Y
unreacted. [This is what I came up with, what do you guys think?}.