Name: ________________________ Class: ___________________ Date: __________ ID: A
Study Guide For Chapter 7
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____ 1. The number of atoms in a mole of any pure substance is called a. its atomic number. c. its mass number.
b. Avogadro’s number. d. its gram-atomic number.
____ 2. What can be said about 1 mol Ag and 1 mol Au?
a. They are equal in mass.
b. They contain the same number of atoms.
c. Their molar masses are equal.
d. They have the same atomic mass.
____ 3. An Avogadro’s number of any element is equivalent to
a. the atomic number of that element. c. 6.022 × 1023 particles.
b. the mass number of that element. d. 12 g of that element.
____ 4. If 0.500 mol of Na+ combines with 0.500 mol of Cl– to form NaCl, how many formula units of NaCl are present?
a. 3.01 × 1023 c. 6.02 × 1024
b. 6.02 × 1023 d. 1.00
____ 5. Using a periodic table, what is the average atomic mass of zinc?
a. 69.723 amu c. 63.546 amu
b. 58.693 amu d. 65.39 amu
____ 6. The atomic mass of hydrogen is 1.008 amu. The reason that this value is not a whole number is that a. hydrogen only exists as a diatomic molecule.
b. the mass of hydrogen is the sum of the masses of the protons and electrons in the atom.
c. the mass of a proton is not exactly equal to 1 amu.
d. hydrogen has more than one isotope.
____ 7. A chemical formula includes the symbols of the elements in the compound and subscripts that indicate a. the number of formula units present.
b. the number of atoms or ions of each type.
c. the formula mass.
d. the charges on the elements or ions.
____ 8. How many atoms of fluorine are in a molecule of carbon tetrafluoride, CF4?
a. 1 c. 4
b. 2 d. 5
____ 9. Changing a subscript in a correctly written chemical formula a. changes the number of moles represented by the formula.
b. changes the charges on the other ions in the compound.
c. changes the formula so that it no longer represents that compound.
d. has no effect on the formula.
____ 10. A formula that shows the simplest whole-number ratio of the atoms in a compound is the a. molecular formula. c. structural formula.
b. ideal formula. d. empirical formula.
____ 11. The molar mass of an element is the mass of one
a. atom of the element. c. gram of the element.
b. liter of the element. d. mole of the element.
Name: ________________________ ID: A
____ 12. To determine the molar mass of an element, one must know the element’s a. Avogadro number. c. number of isotopes.
b. atomic number. d. average atomic mass.
____ 13. What is the molar mass of magnesium?
a. 12.00 g c. 24.305 g
b. 26.982 g d. 22.990 g
____ 14. What is the empirical formula for a compound that is 31.9% potassium, 28.9% chlorine, and 39.2% oxygen?
a. KClO2 c. K2Cl2O3
b. KClO3 d. K2Cl2O5
____ 15. What is the empirical formula for a compound that is 43.6% phosphorus and 56.4% oxygen?
a. P3O7 c. P2O3
b. PO3 d. P2O5
____ 16. What is the empirical formula for a compound that is 53.3% O and 46.7% Si?
a. SiO c. Si2O
b. SiO2 d. Si2O3
____ 17. A compound contains 259.2 g of F and 40.8 g of C. What is the empirical formula for this compound?
a. CF4 c. CF
b. C4F d. CF2
____ 18. A compound contains 64 g of O and 4 g of H. What is the empirical formula for this compound?
a. H2O c. H4O4
b. H2O2 d. HO
____ 19. What is the empirical formula for a compound that is 36.1% Ca and 63.9% Cl?
a. CaCl c. CaCl2
b. Ca2Cl d. Ca2Cl2
____ 20. A compound contains 27.3 g of C and 72.7 g of O. What is the empirical formula for this compound?
a. CO c. C2O
b. CO2 d. C2O4
____ 21. To find the molecular formula from the empirical formula, one must determine the compound’s
a. density. c. structural formula.
b. formula mass. d. crystal lattice.
____ 22. A molecular compound has the empirical formula XY3. Which of the following is a possible molecular formula?
a. X2Y3 c. X2Y5
b. XY4 d. X2Y6
____ 23. The molecular formula for vitamin C is C6H8O6. What is the empirical formula?
a. CHO c. C3H4O3
b. CH2O d. C2H4O2
____ 24. A compound’s empirical formula is NO2. If the formula mass is 92 amu, what is the molecular formula?
a. NO c. NO2
b. N2O2 d. N2O4
____ 25. What is the percentage composition of CF4?
a. 20% C, 80% F c. 16.8% C, 83.2% F
b. 13.6% C, 86.4% F d. 81% C, 19% F
____ 26. What is the percentage composition of CuCl2?
a. 33% Cu, 66% Cl c. 65.50% Cu, 34.50% Cl b. 50% Cu, 50% Cl d. 47.267% Cu, 52.733% Cl
Name: ________________________ ID: A
____ 27. The percentage of sulfur in SO2 is about 50%. What is the percentage of oxygen in this compound?
a. 25% c. 75%
b. 50% d. 90%
____ 28. What is the percentage of OH– in Ca(OH)2?
a. 45.9% c. 75%
b. 66.6% d. 90.1%
Completion
Complete each statement.
29. As the atomic masses of the elements in the periodic table decreases, the number of atoms in one mole of the element ____________________.
30. The unit used for counting numbers of atoms, ions, or molecules is the ____________________.
31. If you have 1.204 × 1024 atoms of nickel, you have ____________________ as the amount of nickel.
32. The number of eggs is to the number of dozens as the number of particles is to the number of ____________________.
33. In one mole of carbon dioxide, CO2, there are ____________________ oxygen atoms.
34. For sodium, the conversion factor that is used to change mass to moles is ____________________.
35. For potassium, the conversion factor that is used to change moles to mass is ____________________.
36. The conversion factor used to change moles to number of particles is ____________________.
37. The element that has an atomic mass of 40.078 amu is ____________________.
38. The average atomic mass of cobalt is ____________________.
39. Comparing the average atomic masses of copper and zinc, the average atomic mass of ____________________ is larger.
40. The empirical formula is always the accepted formula for a(n) ____________________.
41. The empirical formula for a compound shows the symbols of the elements with subscripts indicating the ____________________.
42. In one mole of acetic acid, CH3COOH, there are ____________________ moles of hydrogen atoms.
43. Two moles of carbon atoms are present in ____________________ of C6H6. 44. The unit used for molar mass is ____________________.
45. The molar mass of gallium is ____________________.
46. The molar mass of magnesium oxide, MgO, is ____________________.
47. The molar mass of barium nitrate, Ba(NO3)2, is ____________________.
48. The first step in finding an empirical formula from percentage composition is to assume that you have ____________________ grams of sample.
49. To find an empirical formula from percentage composition, you must divide the number of grams of each element by that element’s ____________________.
Name: ________________________ ID: A
50. If, in determining the empirical formula from percentage composition, your first subscripts show the formula to be Fe1O1.3, you must ______________________________ to obtain the final subscripts.
51. The empirical formula and the formula mass of a compound are needed to determine the compound’s ____________________.
52. A compound’s empirical formula is N2O5. If the formula mass is 108 amu, its molecular formula is ____________________.
53. A compound’s empirical formula is CH3. If the formula mass is 30 amu, its molecular formula is ____________________.
54. To calculate the percentage composition of NiCl2, you need to know ____________________.
55. The percentage of oxygen in NaOH is ____________________.
56. The percentage of sulfur in ammonium sulfate, (NH4)2SO4, is ____________________.
Short Answer
57. Explain the relationship among 6.022 × 1023, one mole, and 12.01 g of carbon.
58. Why will one mole of copper(II) chloride give you more chloride ions than one mole of copper(I) chloride?
59. Explain how you would determine the number of moles of aluminum in 96.7 g of aluminum.
60. Explain how you would calculate the mass in grams of one sodium atom.
61. Describe atomic mass.
62. Describe the atomic mass unit.
63. How are the atomic mass unit and the atomic mass related?
64. Why is the formula for ammonium sulfate written as (NH4)2SO4 and not as N2H8SO4?
65. A student was supposed to find the molar mass of calcium nitrate, Ca(NO3)2. She added the molar masses of calcium, nitrogen, and oxygen. Explain why she did not get the correct value for the molar mass of the compound.
66. Explain the term empirical formula. What is the empirical formula of strontium bromide, SrBr2?
67. You have samples of two compounds. Both contain only iron and chlorine. Explain what you would need to know to determine whether the two samples are the same compound or not.
68. Describe the steps used when determining a molecular formula, given an empirical formula and the molecular mass.
69. Explain how to calculate the percentage of aluminum in AlF3. What is the percentage of Al in AlF3?
Problem
70. The mass of 1 mol of gold atoms is 196.97 g. Find the mass of 1 atom of gold.
71. You have 1.6 × 1021 molecules of oxygen gas, O2. What is the mass of that number of molecules?
Name: ________________________ ID: A
72. What is the mass of 2.5 moles of carbon?
73. How many moles of copper are present in 180.0 g Cu?
74. How many moles of oxygen atoms are present in 2.0 grams of oxygen gas, O2?
75. Argentite is a silver ore that contains 87% silver and 13% sulfur. What is the empirical formula for argentite?
76. Calculate the percentage of sulfur in CuSO4. 77. Calculate the percentage of oxygen in Fe2SiO4. 78. Calculate the percentage of aluminum in Al2O3.
Essay
79. How can you count the number of atoms in a sample of a compound by using a balance?
80. Explain how a chemical formula is related to the mole.
81. Explain how a molecular formula is related to an empirical formula.
ID: A
Study Guide For Chapter 7 Answer Section
MULTIPLE CHOICE
1. ANS: B PTS: 1
2. ANS: B PTS: 1
3. ANS: C PTS: 1
4. ANS: A PTS: 1
5. ANS: D PTS: 1
6. ANS: D PTS: 1
7. ANS: B PTS: 1
8. ANS: C PTS: 1
9. ANS: C PTS: 1
10. ANS: D PTS: 1
11. ANS: D PTS: 1
12. ANS: D PTS: 1
13. ANS: C PTS: 1
14. ANS: B PTS: 1
15. ANS: D PTS: 1
16. ANS: B PTS: 1
17. ANS: A PTS: 1
18. ANS: D PTS: 1
19. ANS: C PTS: 1
20. ANS: B PTS: 1
21. ANS: B PTS: 1
22. ANS: D PTS: 1
23. ANS: C PTS: 1
24. ANS: D PTS: 1
25. ANS: B PTS: 1
26. ANS: D PTS: 1
27. ANS: B PTS: 1
28. ANS: A PTS: 1
COMPLETION
29. ANS: stays the same PTS: 1
30. ANS: mole PTS: 1
31. ANS: two moles PTS: 1
ID: A
32. ANS: moles PTS: 1
33. ANS: 1.204 × 1024 PTS: 1
34. ANS: 1 mol/22.99 g PTS: 1
35. ANS: 39.10 g/1 mol PTS: 1
36. ANS: 6.022 × 1023 particles/1 mol PTS: 1
37. ANS: Ca PTS: 1
38. ANS: 58.93 amu PTS: 1
39. ANS: copper PTS: 1
40. ANS: ionic compound PTS: 1
41. ANS: smallest whole-number ratio of the atoms PTS: 1
42. ANS: four PTS: 1
43. ANS:
0.33 mol one-third mole PTS: 1 44. ANS: g/mol
PTS: 1
45. ANS: 79.72 g/mol PTS: 1
46. ANS: 40.30 g/mol PTS: 1
ID: A
47. ANS: 261.35 g/mol PTS: 1
48. ANS: 100.00 PTS: 1
49. ANS: molar mass PTS: 1
50. ANS: multiply the subscripts by 3 PTS: 1
51. ANS: molecular formula PTS: 1
52. ANS: N2O5
PTS: 1 53. ANS: C2H6
PTS: 1
54. ANS: the molar masses of Ni, Cl, and NiCl2
PTS: 1 55. ANS: 40.00%
PTS: 1 56. ANS: 24.26%
PTS: 1
SHORT ANSWER
57. ANS:
One mole of something equal 6.022 × 1023 units of it. The number 6.022 × 1023 was defined as the number of carbon atoms in exactly 12.01 g of carbon.
PTS: 1
58. ANS:
One mole of copper(II) chloride, CuCl2, provides two moles of Cl– ion per mole of compound. Because copper(I) chloride, CuCl, contains only one mole of Cl– ion per mole of compound, it produces fewer chloride ions.
PTS: 1
ID: A
59. ANS:
You would multiply 96.7 g Al by the mol by the conversion factor 1 mol Al/26.98 g Al. (You would divide 96.7 g Al by the molar mass of Al.)
PTS: 1
60. ANS:
You would multiply the molar mass of sodium, 22.99 g/mol, by the conversion factor 1 mol/6.022 × 1023 atoms.
PTS: 1
61. ANS:
Atomic mass is the sum of the masses of the total number of protons and neutrons in the atom.
PTS: 1
62. ANS:
The atomic mass unit is the average of the mass of the protons and neutrons in the carbon-12 isotope.
PTS: 1
63. ANS:
The atomic mass is the atomic mass unit multiplied by the number of protons and neutrons in the atom.
PTS: 1
64. ANS:
NH4+ is a polyatomic ion that remains a unit and must be treated as a unit in the formula.
PTS: 1
65. ANS:
One mole of the compound contains one mole of Ca, but it contains two moles of N and six moles of O. By adding the mass of one mole of each, the value did not include the mass of the other N and the other five O atoms.
PTS: 1
66. ANS:
The empirical formula shows the simplest whole-number ratio of the atoms that form a compound. The simplest ratio in which strontium and bromine combine is 1:2, so the empirical formula is SrBr2. PTS: 1
67. ANS:
You would need to know the percentage of iron and chlorine in both samples. If the percentage of iron and the percentage of chlorine are the same for both samples, the compounds are the same.
PTS: 1
68. ANS:
Find the mass of the empirical formula. Divide the molecular mass by the mass of the empirical formula.
Multiply the subscripts in the empirical formula by this quotient.
PTS: 1
ID: A
69. ANS:
Divide the molar mass of Al, 26.98 g/mol, by the molar mass of the compound, 83.98 g/mol, then multiply the quotient by 100. The compound is 32.13 % Al.
PTS: 1
PROBLEM
70. ANS:
196.97 g Au
1 mol Au × 1 molAu
6.022×1023atoms Au = 3.271× 10−22g / atom Au PTS: 1
71. ANS:
1.6×1021molecules× 1 molO2
6.022×1023molecules O2
×32.00 g O2
1 molO2
=0.085 g O2
PTS: 1
72. ANS:
2.5 moles C×12.01 g C
1 molC =3.0×101g C PTS: 1
73. ANS:
180.0 g Cu× 1 molCu
63.55 g Cu =2.832 molCu
PTS: 1
74. ANS:
2.0 g O2× 1molO2 32.00 g O2
× 2molO atoms
1 molO2 =0.12mol O atoms
PTS: 1
75. ANS:
87 g Ag × 1 molAg
107.87 g Ag =0.81molAg 13 g S× 1mol S
32.07 g S =0.41mol S 2 mol Ag: 1 mol S; Ag2S PTS: 1
ID: A
76. ANS:
32.07 g/mol 159.62 g/mol
× 100=20.09% S
PTS: 1
77. ANS:
64.00 g/mol 203.79 g/mol
× 100=31.40% O
PTS: 1
78. ANS:
% Al= 53.96 g/mol
101.96 g/mol× 100=52.92% Al PTS: 1
ESSAY
79. ANS:
First, determine the molar mass of the compound. This mass is the amount of compound present in one mole and the amount of compound that contains 6.022 × 1023 formula units of the compound. Then, find the mass of the sample. Divide the sample mass by the molar mass to find out what fraction of a mole is present. Then multiply this number by 6.022 × 1023 to determine the number of formula units present. Multiply this result by the number of atoms present in one formula unit of the compound.
PTS: 1
80. ANS:
The chemical formula identifies the number of each type of element present in a compound. This number is identified as a subscript for values greater than 1, and represents the number of moles of that element present in one mole of the compound.
PTS: 1
81. ANS:
The empirical formula is the simplest ratio of the elements in a compound. The empirical formula is the one used for an ionic compound. The molecular compound shows the actual composition of a molecule and is a multiple of the empirical formula. The empirical and molecular formulas can be the same if the atoms in the molecule exist in the simplest ratio.
PTS: 1
ID: A Study Guide For Chapter 7 [Answer Strip]
_____ 1.B
_____ 2.B
_____ 3.C
_____ 4.A
_____ 5.D
_____ 6.D
_____ 7.B
_____ 8.C
_____ 9.C
_____ 10.D
_____ 11.D
_____ 12.D
_____ 13.C
_____ 14.B
_____ 15.D
_____ 16.B
_____ 17.A
_____ 18.D
_____ 19.C
_____ 20.B
_____ 21.B
_____ 22.D
_____ 23.C
_____ 24.D
_____ 25.B
_____ 26.D
_____ 27.B
_____ 28.A
