This page has all of the required homework for the material covered in the first exam of the first semester of General Chemistry. The textbook associated with this homework is CHEMISTRY The Central Science by Brown, LeMay, et.al. The last edition I required students to buy was the 12th edition (CHEMISTRY The Central Science, 12th ed. by Brown, LeMay, Bursten, Murphy and Woodward), but any edition of this text will do for this course.
Note: You are expected to go to the end of chapter problems in your textbook, find similar questions, and work out those problems as well. This is just the required list of problems for quiz purposes. You should also study the Exercises within the chapters. The exercises are worked out examples of the questions at the back of the chapter. The study guide also has worked out examples.
These are bare-bones questions. The textbook questions will have additional information that may be useful and that connects the problems to real life applications, many of them in biology.
What is the difference between an atom and an element? Answer An atom is the smallest piece of an element that retains the properties of that element.
Define a molecule two different ways. Answer A molecule is two or more atoms that are hooked together, are stuck together, and act as one unit. A molecule is the smallest piece of a substance that retains the properties of that substance.
Do ionic compounds have molecules? Explain. Answer Ionic compounds do not have molecules. There is no single unit that retains the properties of a compound.
Use the periodic table to predict the charge of an ion created from each of the following elements:
K
Answer K+1
Ca
Answer Ca+2
Br
Answer Br-1
Ba
Answer Ba+2
F
Answer F-1
Define the word isotope. Answer Two atoms are isotopes if they have the same number of protons, but a different number of neutrons. Two atoms of the same element that have a different number of neutrons.
Silver has two naturally occurring isotopes: 107Ag (mass = 106.905095 g/mole) has an abundance of 51.83% and 109Ag (mass = 108.904754 g/mole) has an abundance of 48.17. Calculate the molar mass that is reported on the periodic table. Answer 0.5183(106.905095) + 0.4817(108.904754) = 107.868 g/mole
Lithium has two naturally occurring isotopes: 6Li (mass = 6.015123 g/mole) has an abundance of 7.5% and 7Li has an abundance of 92.5%. Calculate the molar mass of 7Li. The periodic table reports 6.941 g/mole for the molar mass of lithium. Answer 0.075(6.015123) + 0.925(x) = 6.941
x = [6.941 - (0.075)(6.015123)]/0.925 = 7.016 g/mole
Boron has two naturally occurring isotopes: 10B (mass = 10.012938 g/mole) and 11B (mass = 11.009305 g/mole). The atomic weight on the periodic table for boron is 10.811 g/mole. Calculate the percent abundance for each isotope. Answer x(10.012938) + (1 - x)(11.009305) = 10.811
x = [10.811 - 11.009305]/[10.012938 - 11.009305] = 0.199
10B is 19.9% and 11B is 80.1%
Identify the following elements and the number of neutrons in the nucleus of the isotope:
3717X
Answer Cl, 20 neutrons
2512X
Answer Mg, 13 neutrons
7031X
Answer Ga, 39 neutrons
24395X
Answer Am, 148
How many protons, neutrons, and electrons are in the following isotopes:
35Cl
Answer 17 protons, 18 neutrons, and 17 electrons
85Sr2+
Answer 38 protons, 47 neutrons, and 36 electrons
131I-
Answer 53 protons, 78 neutrons, 54 electrons
129Cs
Answer 55 protons, 74 neutrons, 55 protons
Fill in the following table:
Symbol
56Fe3+
Protons
29
55
Neutrons
34
78
7
Electrons
28
10
Net Charge
0
2-
Answer
Symbol
56Fe3+
63Cu+
133Cs
15O2-
Protons
26
29
55
8
Neutrons
30
34
78
7
Electrons
23
28
55
10
Net Charge
3+
1+
0
2-
Predict the compounds formed by combining the cations across the top with the anions down the side.
Ion
Zn2+
Na+
Ba2+
Al3+
SO42-
NO3-
CO32-
OH-
Cl-
PO43-
Answer
Ion
Zn2+
Na+
Ba2+
Al3+
SO42-
ZnSO4
Na2SO4
BaSO4
Al2(SO4)3
NO3-
Zn(NO3)2
NaNO3
Ba(NO3)2
Al(NO3)3
CO32-
ZnCO3
Na2CO3
BaCO3
Al2(CO3)3
OH-
Zn(OH)2
NaOH
Ba(OH)2
Al(OH)3
Cl-
ZnCl2
NaCl
BaCl2
AlCl3
PO43-
Zn3(PO4)2
Na3PO4
Ba3(PO4)2
AlPO4
Give the name or formula for each of the following compounds.
CuCl
Answer Copper(I)chloride
HgCO3
Answer Mercury(II)carbonate
FeBr3
Answer Iron(III)bromide
Chromium(III)acetate
Answer Cr(C2H3O2)3
Lead(II)hydroxide
Answer Pb(OH)2
Manganese(II)nitrate
Answer Mn(NO3)2
Give the name or formula for each of the following molecules.
Cl2O
Answer dichlorine monoxide
N2O4
Answer dinitrogen tetroxide
NF3
Answer nitrogen trifluoride
chlorine pentaflouride
Answer ClF5
Dinitrogen oxide
Answer N2O
Phosphorous trichloride
Answer PCl3
Balance the following chemical equations.
CH4 + O2 → H2O + CO2
Answer CH4 + 2O2 → 2H2O + CO2
HgCO3 + HCl → H2O + CO2 + HgCl2
Answer HgCO3 + 2HCl → H2O + CO2 + HgCl2
FeBr3 + AgNO3 → Fe(NO3)3 + AgBr
Answer FeBr3 + 3AgNO3 → Fe(NO3)3 + 3AgBr
H2 + O2 → H2O
Answer H2 + ½O2 → H2O or 2H2 + O2 → 2H2O
K + N2 → K3N
Answer 6K + N2 → 2K3N
Al(OH)3 + H2SO4 → Al2(SO4)3 + H2O
Answer 2Al(OH)3 + 3H2SO4 → Al2(SO4)3 + 6H2O
Calculate the formula weights (also called molecular weight or molar mass) of the following substances. See Chapter Three problems for interesting examples.
Ammonium hydroxide
Answer NH4OH ⇒35 g/mole
HgCO3
Answer 260.59 g/mole
H2SO4
Answer 98 g/mole
Copper(II)chloride
Answer CuCl2 ⇒ 134.452 g/mole
Calculate the percentage by mass of the indicated element in the following substances.
Oxygen in ammonium hydroxide
Answer NH4OH ⇒ 16/35 = 0.457 ⇒ 45.7%
Hg in HgCO3
Answer 200.59/260.59 = .767 ⇒ 76.7%
N in Fe(NO3)3
Answer (3*14)/241.845 = .174 ⇒ 17.4%
Chlorine in copper(II)chloride
Answer CuCl2 ⇒ (2*35.453)/134.452 = 0.527 52.7%
What is a mole? Where are the conversion factors between grams and moles found? Answer 1 mole = 6.02 x 1023 objects. The atomic mass on the periodic table is the number of grams associated with one mole of that element.
Calculate the following:
How many grams are in 1.5 moles of atomic nitrogen?
Answer
(
1.5 mole N
)
(
)
= 21 g N
How many grams of nitrogen are in 1.5 moles of gaseous nitrogen (N2)?
Answer
(
1.5 mole N2
)
(
)
(
)
= 42 g N
How many moles of Br are in 79.9 g of Br2?
Answer
(
79.9 g Br2
)
(
)
(
)
= 1.0 mole Br
How many moles of O2 are there in 32 g O2?
Answer
(
32 g O2
)
(
)
= 1 mole O2
Calculate the empirical formulas.
What is the empirical formula for acetone, a common solvent, if it is 62.07% carbon, 27.59% oxygen, and 10.34% hydrogen?
Answer
(
62.07 g C
)
(
)
= 5.17 mole C
(
27.59 g O
)
(
)
= 1.72 mole O
(
10.34 g H
)
(
)
= 10.34 mole H
(
)
= 3
(
)
= 1
(
)
= 6
⇒ C, 3; O, 1; H, 6 ⇒ C3H6O
What is the empirical formula for phenol if a sample analysis yielded 0.32 g hydrogen, 0.85 g oxygen, and 3.83 g carbon?
Answer
(
0.32 g H
)
(
)
= 0.32 mole H
(
0.85 g O
)
(
)
= 0.053 mole O
(
3.83 g C
)
(
)
= 0.319 mole C
(
0.320 mole H
0.053 mole O
)
= 6
(
0.053 mole O
0.053 mole O
)
= 1
(
0.319 mole C
0.053 mole O
)
= 6
⇒ C, 6; H, 6; O, 1 ⇒ C6H6O
What is the empirical formula of an aluminum oxide sample if it is 52.92% aluminum and 47.08% oxygen?
Answer
(
52.92 g Al
)
(
)
= 1.96 mole Al
(
47.08 g O
)
(
)
= 2.94 mole O
(
1.96 mole Al
1.96 mole Al
)
= 1
(
)
= 1.5
⇒ Al, 1; O, 1.5 ⇒ Al, 2; O, 3 ⇒ Al2O3
A common organic solvent only contains carbon, hydrogen, and oxygen. Combustion analysis of 1.000 g of this solvent gives 1.913 g CO2 and 1.174 g H2O. What is the empirical formula?
Answer
(
1.913 g CO2
)
(
)
(
)
= 0.0435 mole C
(
1.174 g H2O
)
(
)
(
)
= 0.130 mole H
(
0.0435 mole C
)
(
)
= 0.522 g C
(
0.130 mole H
)
(
)
= 0.13 g H
1.000 g sample - 0.522 g C - 0.130 g H = 0.348 g O
(
0.348 g O
)
(
)
= 0.0218 mole O
(
0.0435 mole C
0.0218 mole O
)
= 2
(
0.130 mole H
0.0218 mole O
)
= 6
(
0.218 mole O
0.0218 mole O
)
= 1
⇒ C, 2; H, 6; O, 1 ⇒ C2H6O (ethanol or ethyl alcohol)
In combustion reactions carbon-containing substances react with oxygen to form carbon dioxide and water. Burning ethanol is an example:
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g)
How many moles of O2 are needed to react with 1.5 moles of C2H5OH?
Answer
(
1.5 mole C2H5OH
)
(
)
= 4.5 mole O2
How many moles of CO2 are produced when when 1.5 moles of C2H5OH are burned?
Answer
(
1.5 mole C2H5OH
)
(
)
= 3 mole CO2
How many moles of oxygen are needed to produce 3.3 moles of carbon dioxide?
Answer
(
3.3 mole CO2
)
(
)
= 2.2 mole O2
How many grams of C2H5OH are needed to produce 36 g H2O?
Answer
(
36 g H2O
)
(
)
= 2 mole H2O
(
2 mole H2O
)
(
)
(
46 g C2H5OH
1 mole C2H5OH
)
= 30.67 g C2H5OH
How many grams of CO2 are produced when 15 g O2 are reacted?
Answer
(
15 g O2
)
(
)
(
)
(
)
= 13.75 g CO2
How many mole of CO2 are produced when 4 moles of O2 are reacted with 1.5 moles of C2H5OH?
Answer Determine limitiing reactant by choosing one reactant and determining the amount of the other one that is needed to completely react. I have chosen O2 below.
(
4 mole O2
)
(
)
= 1.33 mole C2H5OH needed
We need 1.33 moles, but we have 1.5 moles according to the problem statement. We have extra C2H5OH which means that O2 is the limiting reactant. Use the amount of limiting reactant that we have to determine the amount of product produced.
(
4 mole O2
)
(
)
= 2.67 mole CO2
How many grams of H2O are produced when 256 g of O2 are reacted with 138 g of C2H5OH?
Answer
Determine the moles of each reactant that we are given:
(
256 g O2
)
(
)
= 8 mole O2
(
138 g C2H5OH
)
(
1 mole C2H5OH
46 g C2H5OH
)
= 3 mole C2H5OH
Determine limitiing reactant by choosing one reactant and determining the amount of the other one that is needed to completely react. I have chosen C2H5OH below. Get the mole ratios from the balanced equation.
(
3 mole C2H5OH
)
(
)
= 9 mole O2 needed
We need 9 mole O2, but have 8 moles. We don't have enough O2 which means that O2 is the limiting reactant. Use the amount of limiting reactant that we have to determine the amount of product produced.
(
8 mole O2
)
(
)
(
)
= 144 g H2O
How many grams of Fe2O3 are produced when 56 g of Fe are reacted with 32 g of O2? How many grams of the excess reactant will remain after the reaction is complete?
4Fe(s) + 3O2(g) → 2Fe2O3(s)
Answer
Determine the moles of each of the reactants that we are given.
(
32 g O2
)
(
)
= 1 mole O2
(
56 g Fe
)
(
)
= 1 mole Fe
Determine limitiing reactant by choosing one reactant and determining the amount of the other one that is needed to completely react. I have chosen Fe below. Get the mole ratios from the balanced chemical equation.
(
1 mole Fe
)
(
)
= 0.752 mole O2 needed
We need 0.752 mole O2, but have 1 mole. We have extra O2 which means that Fe is the limiting reactant. Use the amount of limiting reactant that we have to determine the amount of product produced.
(
56 g Fe
)
(
)
(
)
(
159.69 g Fe2O3
1 mole Fe2O3
)
= 80.07 g Fe2O3
We have 1 mole - 0.752 mole = 0.248 moles of extra O2
(
0.248 mole O2
)
(
)
= 7.94 g O2 left over
How many grams of Fe2O3 are produced when 56 g of Fe are reacted with 32 g of O2? How many grams of the excess reactant will remain after the reaction is complete?
4Fe(s) + 3O2(g) → 2Fe2O3(s)
Answer
Determine the moles of each of the reactants that we are given.
(
32 g O2
)
(
)
= 1 mole O2
(
56 g Fe
)
(
)
= 1 mole Fe
Determine limitiing reactant by choosing one reactant and determining the amount of the other one that is needed to completely react. I have chosen Fe below. Get the mole ratios from the balanced chemical equation.
(
1 mole Fe
)
(
)
= 0.752 mole O2 needed
We need 0.752 mole O2, but have 1 mole. We have extra O2 which means that Fe is the limiting reactant. Use the amount of limiting reactant that we have to determine the amount of product produced.
(
56 g Fe
)
(
)
(
)
(
159.69 g Fe2O3
1 mole Fe2O3
)
= 80.07 g Fe2O3
We have 1 mole - 0.752 mole = 0.248 moles of extra O2
(
0.248 mole O2
)
(
)
= 7.94 g O2 left over
Problem for limiting reactant lab: Aluminum hydroxide reacts with sulfuric acid as follows:
Determine the limiting reactant when 0.600 mole Al(OH)3 and 0.600 mole H2SO4 are allowed to react? How many moles of Al2(SO4)3 can form under these conditions? How many moles of the excess reactant remain after the completion of the reaction? Show all work!
