Department of Chemistry, Geosciences, and Environmental Science
Chemistry 1054-010 College Chemistry Summer I 2005
Exam 1-Key
Name:_______________________________________________________
(Please write your name legibly)
Read all directions and questions carefully!! This exam consists of two parts. The first part consists of 10 multiple choice questions worth four points each for a total of 40 points. The second part consists of five numerical problems worth either 10 or 15 points per question for a total of 60 points. Show all your work necessary for the numerical problems as partial credit will be given for those problems.
Possibly Useful Constants
Avogadro’s Number: NA = 6.022 × 1023 particles/mol
Polyatomic ions
Ammonium ion: NH4+ Hydroxide ion: OH¯
Sulfate ion: SO42- Nitrate ion: NO3¯
Carbonate ion: CO32- Phosphate ion: PO43-
Cyanide ion: CN¯ Acetate ion: C2H3O2¯
Score
Part 1 (40 points):_____________________
Part 2 (60 points):_____________________
Total (100 points):_____________________
Don’t forget to put your name on this test!
Good Luck!!
Part 1
Multiple Choice
Please indicate the answer to each question by putting your choice in the space provided. There is only one correct answer for each question. There will be 10 multiple choice questions worth 4 points each.
1. If the components of a form of matter are uniform throughout, cannot be separated by physical processes but can be decomposed into simpler substances by chemical processes, it is called a (an) ___________.
(a) heterogeneous mixture (c) homogeneous mixture
(b) element (d) compound
(e) solution
Answer: D
2. The S. I. unit for mass is the _______________.
(a) kilogram (c) pound
(b) gram (d) ounce
(e) ton
Answer: A
3. The metric prefix meaning 10-6 (or one-millionth) of the base unit is:
(a) Mega- (c) centi-
(b) kilo- (d) milli-
(e) micro-
Answer: E
4. There are _________ significant figures in the answer to the following computation:
(a) 1 (c) 3
(b) 2 (d) 4
(e) 5
Answer: B (The result of 29.2 – 20.0 = 9.2 which has two sig figs)
5. Which experiment determined the charge on the electron?
(a) Thomson’s cathode ray tube experiment (c) Rutherford’s gold foil experiment
(b) the
Answer: D
6. The formula for the salt formed when lithium ion combines with phosphate ion is:
(a) LiPO4 (c) Li3PO4
(b) Li(PO4)2 (d) Li2PO4
(e) Li3(PO4)2
Answer: C (The group charge on lithium is Li+, the charge for the phosphate ion is PO43-)
7. Ammonia reacts with oxygen to produce nitrogen monoxide and water according to the reaction:
4 NH3(g) + 5 O2(g) ¾¾® 4 NO(g) + 6 H2O(g)
How many moles of oxygen are needed to reaction with 2.5 mol of NH3?
(a) 2.5 mol (c) 4.0 mol
(b) 5.0 mol (d) 2.0 mol
(e) 3.1 mol
Answer: E 
8. What is the coefficient in front of sulfuric acid in the following equation after it is balanced?
Mg3N2(s) + H2SO4(aq) ¾¾® MgSO4(aq) + (NH4)2SO4(aq)
(a) 1 (c) 3
(b) 2 (d) 4
(e) 5
Answer: D (The balanced reaction is: Mg3N2(s) + 4 H2SO4(aq) ¾® 3 MgSO4(aq) + (NH4)2SO4(aq))
9. The formula of nitrobenzene is C6H5NO2. The formula weight of this compound is:
(a) 107.1 amu (c) 109.1 amu
(b) 43.03 amu (d) 123.1 amu
(e) 3.06 amu
Answer: D
10. Both the definition of the mole and of the atomic mass unit are based on which isotope?
(a) hydrogen-1 (c) oxygen-16
(b) carbon-12 (d) iron-56
(e) helium-4
Answer: B
Part 2
Numerical Problems
Solve the following problems, keeping track of significant figures where applicable. Please show all the work necessary to obtain your answer in order to receive partial credit for possibly wrong answers. Generally, full credit will not be given for the correct answer without any of the work performed to obtain the answer being shown on the paper. Each question is worth either 10 or 15 points.
11. (10 points) Perform the following unit conversions:
(a) 41.36 mL to L
Conversion: 1000 mL = 1 L
(b) 75 g to oz. (1 lb = 453.59 g, 16 oz = 1 lb)
(c) –5°F to °C 
(d) 3.78 × 108 cm3 to m3
Conversion: 102 cm = 1 m
First, cube the conversion factor:
Now, perform the conversion from cm3 to m3:
12. (15 points) A natural sample of thallium (Tl) contains two isotopes: 203Tl with an atomic mass of 202.972329 amu and an abundance of 29.524%; and 205Tl with an atomic mass of 204.974412 amu and an abundance of 70.476%. Calculate the atomic weight of thallium from this information.
Take the weighted average of the atomic masses:
13. (10 points) Calculate the number of moles in 3.25 g of Mg(NO3)2.
Calculate the molar mass of Mg(NO3)2:
Converting from grams to moles:
14. (10 points) Give the number of protons, neutrons, and electrons in each of the species shown in the table below:
Symbol |
Number of protons |
Number of neutrons |
Number of electrons |
|
62 |
88(=150–62) |
62 |
|
82 |
125(=207–82) |
80(=82–2) |
|
35 |
46(=81–35) |
36(=35–(-1)) |
|
40 |
51(=91–40) |
40 |
|
7 |
8(=15–7) |
10(=7–(-3)) |
15. (15 points) The smell of bananas is due to the compound called isopentyl acetate. Its composition is 64.58% C, 10.84% H, and 24.58% O by mass. It has a molar mass of 130.2 g/mol. What is the molecular formula of isopentyl acetate?
Assuming exactly 100 grams of compound, calculate the empirical formula for isopentyl acetate:
The empirical formula is C7H14O2. The empirical formula weight is 130.2 g/mol. Since this is equal to the molar mass, the empirical formula is the empirical formula, C7H14O2.
10 points extra credit Please give the complete definition for 2 out of following three terms. You will be given 5 points for each definition. Only answer 2 out of the three, if you answer all 3 only the first two will be graded.
Atomic mass unit: exactly 1/12 the mass of a carbon-12 atom.
Law of constant composition: a particular compound always has the same composition.
Precision: how close a collection of repeated measurements are to each other.