Part A. Multiple Choice (21 points)
If printing out the exam: indicate your choice by circling the corresponding letter.
If answering questions on a separate sheet of paper: indicate your choice by writing down the corresponding letter.
1. Which of the following is NOT a chemical compound?
a) Water
c) Table salt (sodium chloride)
b) Carbon dioxide
d) Zinc
2. How many protons, neutrons, and electrons are in 114Cd2+?
a) 0 protons, 114 neutrons, 2 electrons
c) 48 protons, 66 neutrons, 48 electrons
b) 48 protons, 114 neutrons, 46 electrons
d) 48 protons, 66 neutrons, 46 electrons
3. Which element is most likely to form a cation with a +3 charge?
a) Aluminum
c) Nitrogen
b) Fluorine
d) Sulfur
4. What percentage of the mass of styrene (C8H8) is due to carbon?
a) 12%
c) 92%
b) 50%
d) 96%
5. How many gold atoms are in 10.0 grams of pure gold (Au)?
a) 3.06 × 1022
c) 6.02 × 1024
b) 1.19 × 1024
d) 8.43 × 1023
6. Which of the following is an empirical formula?
a) C2H8N2
c) N2O5
b) C5H10
d) P4O10
7. If 1.0 g of glucose (C6H12O6) is fully dissolved in water to create 35.0 mL of solution with a mass of
36.4 g, what is the molarity of glucose in this solution?
a) 1.6 × 10–4 M
c) 0.027 M
e) 6.3 M
b) 0.16 M
d) 0.029 M
f) 0.96 M
Part B (30 points)
8. What is the number of significant figures in each of the following measured quantities? (8 points)
(1) 0.0250 lb _3_ significant figure(s)
(3) 620 cm _2_ significant figure(s)
(2) 94.0 ounces _3_ significant figure(s)
(4) 61000000.0 m3 _9_ significant figure(s)
9. Give the name or chemical formula, as appropriate, for each of the following compounds: (8 points)
potassium acetate
(1) CH3COOK
(2) iron(II) phosphate
(3) strontium cyanide
(4) Hg2(NO3)2
Fe3(PO4)2
Sr(CN)2
mercury(I) nitrate
Answer the following questions, writing out the intermediate steps and showing your work in general.
10. The concentration of carbon monoxide in a home is 5.0 mg/m3. The home measures 10.93 yd ×
16.67 yd × 4.83 yd. Using the conversion factors available to you in Handout 1, calculate the total
mass (in grams) of carbon monoxide present in the house. (7 points)
Volume of home:
10.93 yd × 16.67 yd × 4.83 yd = 880.04 = 880 yd3
880.04
yd3
×
(1 m)3
(1.0936 yd)3
5.0 mg
×
1 m3
×
1 × 10-3 g
1 mg
= 3.364 = 3.4 g
11. A U.S. penny (one-cent coin) contains 2.95 grams of copper. The current price of copper is $8139
per US ton (1 US ton = 907.185 kg). Calculate how many cents the copper in each penny is worth.
(7 points)
Price of copper in $/gram:
$8139
1 US ton
$ 0.0089717
g
1 US ton
×
907.185 kg
×
100 ¢
1$
×
1 kg
1000 g
= 0.0089717 = 0.008972 = $8.972 × 10-3 per gram
× 2.95 g = 2.647 = 2.65 ¢
Part C (28 points)
Answer the following questions, writing out the intermediate steps and showing your work in general. You do not
need to show your work for 12(b).
12. Sodium tetraborate, also known as Borax, has many industrial and household uses.
(a) The chemical formula of sodium tetraborate is often written as Na2B4O7. Using this formula, calculate the
molar mass of sodium tetraborate to 2 decimal places. (5 points)
FW of Na2B4O7: 2 × 22.99 + 4 × 10.81 + 7 × 16.00 = 201.22 amu
Molar mass: 201.22 g/mol
(b) Sodium tetraborate reacts with sulfuric acid to produce boric acid (H3BO3):
Na2B4O7 (s) + H2SO4 (aq) + H2O
Na2SO4 (aq) + H3BO3 (aq)
Balance this chemical equation and write out the balanced equation below. (5 points)
Na2B4O7 (s) + H2SO4 (aq) + 5 H2O
Na2SO4 (aq) + 4 H3BO3 (aq)
(c) If 100.0 g of sodium tetraborate and 75 mL of 6.00 M H2SO4 are to react according to the equation above,
determine the limiting reactant and calculate the the mass of H3BO3 generated from this reaction in
grams, assuming 91% yield. (You can assume that H2O is not the limiting reactant.) (12 points)
1 mol Na2B4O7
100.0 g Na2B4O7 ×
75 mL H2SO4 ×
201.22 g Na2B4O7
1L
1000 mL
×
6.00 M
L
= 0.49697 = 0.4970 mol
= 0.45 mol
Because the molar ratio of Na2B4O7 to H2SO4 is 1:1 in the equation,
H2SO4 is the limiting reactant.
Formula Weights
Na2B4O7: ?? amu
H2SO4: 98.08 amu
H2O: 18.02 amu
Na2SO4: 142.04 amu
H3BO3: 61.83 amu
Theoretical yield of H3BO3:
4 mol H3BO3
0.45 mol H2SO4 ×
×
1 mol H2SO4
Actual yield of H3BO3:
111.294 g × 91%
61.83 g H3BO3
1 mol H3BO3
= 111.294 = 1.1 × 102 g
= 101.278 = 1.0 × 102 g
100%
(d) Calculate the amount of excess reactant that is leftover from the reaction in part (c). (If the excess
reactant is sodium tetraborate, express your result in grams; if the excess reactant is sulfuric acid,
express your result in mL.) (6 points)
Mass of Na2B4O7 consumed:
0.45 mol H2SO4 ×
1 mol Na2B4O7
1 mol H2SO4
×
201.22 g Na2B4O7
1 mol Na2B4O7
Mass of Na2B4O7 leftover: 100.0 g – 90.549 g = 9.451 = 9.5 g
= 90.549 = 91 g
Part D (21 points)
Answer the following question(s), writing out the intermediate steps and showing your work in general.
13. Heavy water is used in the nuclear reactors of many nuclear power plants around the world. In this type
of water, hydrogen-2 (mass: 2.014 amu, also called “deuterium”) has an abundance of 99.75%, while
hydrogen-1 (mass: 1.0078 amu, also called “protium”) has an abundance of 0.25%. Calculate the atomic
weight (average atomic mass) of hydrogen in this type of water. (6 points)
Atomic weight (average atomic mass) = Σ fractional abundance × mass of isotope
Atomic weight = 2.014 × 0.9975 + 1.0078 × 0.0025 = 2.01148 = 2.0 amu
14. A 8.086-gram sample of a compound that contains only C, H and O is analyzed by combustion analysis.
11.466 grams of CO2 and 7.042 grams of H2O are produced. Determine the empirical formula of the
compound. (15 points)
Formula Weights
Molar mass of CO2: 44.01 g/mol
Molar mass of H2O: 18.02 g/mol
11.466 g CO2 ×
7.042 g H2O ×
1 mol CO2
1 mol C
×
1 mol CO2
44.01 g CO2
1 mol H2O
×
18.02 g H2O
2 mol H
1 mol H2O
CO2: 44.01 amu
H2O: 18.02 amu
= 0.2605 mol C
= 0.7816 mol H
Mass of O in sample:
8.086 g – 0.2605 mol C ×
12.01 g C
1 mol C
– 0.7816 mol H ×
1.008 g H
= 4.1696 = 4.170 g O
1 mol H
# moles of O in sample:
4.1696 g O ×
1 mol O
= 0.2606 mol O
16.00 g O
0.2606 mol O
0.2605 mol C
0.7816 mol H
0.2605 mol C
= 1.0004 = 1
= 3.0004 = 3
The empirical formula is CH3O.
Honor Pledge
Write down the following sentence: I have adhered to the Honor Code in completing this exam.