Department of Chemistry, Geosciences, and Environmental Science
Chemistry 1054-010 College Chemistry Fall 2005
Exam 1-A-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
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. What is the physical state in which matter has no specific shape but does have a specific volume?
(a) gas (c) liquid
(b) solid (d) salts
(e) ice
Answer: C
2. Which one of the following is not a chemical change?
(a) dissolving sugar in coffee.
(b) burning a candle.
(c) cooking an egg.
(d) forming rust on steel knives.
(e) all of the above are chemical changes.
Answer: A
3. The number 0.00430 has ___________significant figures.
(a) 2 (c) 5
(b) 3 (d) 6
(e) 4
Answer: B
4. Elements in group 2A are called the
(a) alkali metals (c) chalcogens
(b) halogens (d) noble gases
(e) alkaline earth metals
Answer: E
5. Fluorine forms a monatomic ion with a charge of:
(a) +3 (c) +2
(b) +1 (d) –1
(e) –3
Answer: D
6. The gold foil experiment performed in
(a) confirmed the plum-pudding model of the atom.
(b) led to the discovery of the atomic nucleus.
(c) studied the deflection of beta particles when passed through a gold foil.
(d) proved the law of multiple proportions.
Answer: B
7. There are ___________ atoms of oxygen in 300 molecules of CH3CO2H.
(a) 300 (c) 3.01 × 1024
(b) 600 (d) 3.61 × 1026
(e) 1.80 × 1026
Answer: D
8. The combustion of ammonia is represented by the following reaction:
4 NH3(g) + 7 O2(g) ¾¾® 4 NO2(g) + 6 H2O(g)
How many moles of NH3 are required to produce 0.500 mol of H2O?
(a) 0.0833 mol (c) 0.750 mol
(b) 0.333 mol (d) 0.500 mol
Answer: B
9. Suppose that when the above combustion reaction is performed with the same amounts of reactants as required in problem 8, only 7.21 g of H2O was collected in the lab. What is the %yield for this reaction?
(a) 100% (c) 80.0%
(b) 120% (d) 72.1%
(e) 90.1%
Answer: C
10. What is the formula of the salt consisting of the monatomic ions of lithium and oxygen?
(a) LiO2 (c) Li2O
(b) Li2O3 (d) Li3O2
(e) LiO
Answer: C
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) Fill in the blanks in the following table:
The answers are placed in italics in the boxes:
Symbol |
Number of protons |
Number of Neutrons |
Number of electrons |
Net charge |
|
44 |
57=(101–44) |
44 |
0 |
|
51 |
71=(122–51) |
54=(51–(–3) |
-3 |
|
33 |
42 |
33 |
0 |
|
38 |
50 |
36 |
+2=(38–36) |
|
52 |
76 |
54=(52–(-2) |
2– |
12. (15 points) Perform the following unit conversions:
(a) 284.3 ms to s
1000 ms = 1 s
(b) 1255 g to lb (453.59 g = 1 lb)
(c) 35 mi/h (miles per hour) to m/s (1 mi = 1.6093 km)
1000 m = 1 km and 3600 s = 1 h
(d) 2.19 × 10-5 m3 to cm3
102 cm = 1 m First you must cube this conversion: (102 cm)3 = (1 m)3¾® 106 cm3 = 1 m3
(e) –35°F to °C 
13. (10 points) A natural sample of gallium (Ga) consists of two isotopes: 69Ga with an atomic mass of 68.925581 amu and a 60.108% abundance; and 71Ga with an atomic mass of 70.924707 amu and a 39.892% abundance. Calculate the atomic weight of gallium from this information.
The atomic weight is the weighted average of the atomic masses. Taking the weighted average:
The atomic weight is equal to 69.723 amu.
14. (10 points) How many grams are there in 0.210 mol of Ca3(PO4)2?
Calculate the molar mass of Ca3(PO4)2:
The molar mass of Ca3(PO4)2 is 310.1 g/mol. Converting from moles to grams:
15. (15 points) The elemental composition of a particular molecule is 43.62%C, 5.49%H, and 50.89%N by mass. The molar mass of the compound is equal to 220.2 g/mol. What is the molecular formula of the compound?
Assume 100 grams of the compound:
The empirical formula is C2H3N2. Calculating the empirical formula weight:
Divide this formula weight into the molar mass:
The molecular formula is 4 times the empirical formula or C8H12N8.