Study Guide For Chapter 7

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 10 23 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 10 23 c. 6.02 10 24 b. 6.02 10 23 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, CF 4? 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 c. changes the formula so that it no longer represents that compound.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. 1

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. KClO 2 c. K 2 Cl 2 O 3 b. KClO 3 d. K 2 Cl 2 O 5 15. What is the empirical formula for a compound that is 43.6% phosphorus and 56.4% oxygen? a. P 3 O 7 c. P 2 O 3 b. PO 3 d. P 2 O 5 16. What is the empirical formula for a compound that is 53.3% O and 46.7% Si? a. SiO c. Si 2 O b. SiO 2 d. Si 2 O 3 17. A compound contains 259.2 g of F and 40.8 g of C. What is the empirical formula for this compound? a. CF 4 c. CF b. C 4 F d. CF 2 18. A compound contains 64 g of O and 4 g of H. What is the empirical formula for this compound? a. H 2 O c. H 4 O 4 b. H 2 O 2 d. HO 19. What is the empirical formula for a compound that is 36.1% Ca and 63.9% Cl? a. CaCl c. CaCl 2 b. Ca 2 Cl d. Ca 2 Cl 2 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. C 2 O b. CO 2 d. C 2 O 4 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 XY 3. Which of the following is a possible molecular formula? a. X 2 Y 3 c. X 2 Y 5 b. XY 4 d. X 2 Y 6 23. The molecular formula for vitamin C is C 6 H 8 O 6. What is the empirical formula? a. CHO c. C 3 H 4 O 3 b. CH 2 O d. C 2 H 4 O 2 24. A compound s empirical formula is NO 2. If the formula mass is 92 amu, what is the molecular formula? a. NO c. NO 2 b. N 2 O 2 d. N 2 O 4 25. What is the percentage composition of CF 4? 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 CuCl 2? a. 33% Cu, 66% Cl c. 65.50% Cu, 34.50% Cl b. 50% Cu, 50% Cl d. 47.267% Cu, 52.733% Cl 2

Name: ID: A 27. The percentage of sulfur in SO 2 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 10 24 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, CO 2, 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, CH 3 COOH, there are moles of hydrogen atoms. 43. Two moles of carbon atoms are present in of C 6 H 6. 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(NO 3 ) 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. 3

Name: ID: A 50. If, in determining the empirical formula from percentage composition, your first subscripts show the formula to be Fe 1 O 1.3, 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 N 2 O 5. If the formula mass is 108 amu, its molecular formula is. 53. A compound s empirical formula is CH 3. If the formula mass is 30 amu, its molecular formula is. 54. To calculate the percentage composition of NiCl 2, you need to know. 55. The percentage of oxygen in NaOH is. 56. The percentage of sulfur in ammonium sulfate, (NH 4 ) 2 SO 4, is. Short Answer 57. Explain the relationship among 6.022 10 23, 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 (NH 4 ) 2 SO 4 and not as N 2 H 8 SO 4? 65. A student was supposed to find the molar mass of calcium nitrate, Ca(NO 3 ) 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, SrBr 2? 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 AlF 3. What is the percentage of Al in AlF 3? 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 10 21 molecules of oxygen gas, O 2. What is the mass of that number of molecules? 4

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, O 2? 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 CuSO 4. 77. Calculate the percentage of oxygen in Fe 2 SiO 4. 78. Calculate the percentage of aluminum in Al 2 O 3. 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. 5

ID: A Study Guide For Chapter 7 Answer Section MULTIPLE CHOICE 1. ANS: B 2. ANS: B 3. ANS: C 4. ANS: A 5. ANS: D 6. ANS: D 7. ANS: B 8. ANS: C 9. ANS: C 10. ANS: D 11. ANS: D 12. ANS: D 13. ANS: C 14. ANS: B 15. ANS: D 16. ANS: B 17. ANS: A 18. ANS: D 19. ANS: C 20. ANS: B 21. ANS: B 22. ANS: D 23. ANS: C 24. ANS: D 25. ANS: B 26. ANS: D 27. ANS: B 28. ANS: A COMPLETION 29. ANS: stays the same 30. ANS: mole 31. ANS: two moles 1

ID: A 32. ANS: moles 33. ANS: 1.204 10 24 34. ANS: 1 mol/22.99 g 35. ANS: 39.10 g/1 mol 36. ANS: 6.022 10 23 particles/1 mol 37. ANS: Ca 38. ANS: 58.93 amu 39. ANS: copper 40. ANS: ionic compound 41. ANS: smallest whole-number ratio of the atoms 42. ANS: four 43. ANS: 0.33 mol one-third mole 44. ANS: g/mol 45. ANS: 79.72 g/mol 46. ANS: 40.30 g/mol 2

ID: A 47. ANS: 261.35 g/mol 48. ANS: 100.00 49. ANS: molar mass 50. ANS: multiply the subscripts by 3 51. ANS: molecular formula 52. ANS: N 2 O 5 53. ANS: C 2 H 6 54. ANS: the molar masses of Ni, Cl, and NiCl 2 55. ANS: 40.00% 56. ANS: 24.26% SHORT ANSWER 57. ANS: One mole of something equal 6.022 10 23 units of it. The number 6.022 10 23 was defined as the number of carbon atoms in exactly 12.01 g of carbon. 58. ANS: One mole of copper(ii) chloride, CuCl 2, 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. 3

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.) 60. ANS: You would multiply the molar mass of sodium, 22.99 g/mol, by the conversion factor 1 mol/6.022 10 23 atoms. 61. ANS: Atomic mass is the sum of the masses of the total number of protons and neutrons in the atom. 62. ANS: The atomic mass unit is the average of the mass of the protons and neutrons in the carbon-12 isotope. 63. ANS: The atomic mass is the atomic mass unit multiplied by the number of protons and neutrons in the atom. 64. ANS: NH 4 + is a polyatomic ion that remains a unit and must be treated as a unit in the formula. 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. 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 SrBr 2. 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. 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. 4

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. PROBLEM 70. ANS: 196.97gAu 1molAu 1molAu 6.022 10 23 atomsau = 3.271 10 22 g/atomau 71. ANS: 1molO2 1.6 10 21 molecules 6.022 10 23 molecules O2 32.00gO 2 1molO2 = 0.085gO2 72. ANS: 2.5moles C 12.01gC 1molC =3.0 101 gc 73. ANS: 180.0gCu 1molCu = 63.55gCu 2.832molCu 74. ANS: 2.0gO 2 1molO 2 32.00gO 2 2molOatoms 1molO 2 =0.12mol O atoms 75. ANS: 87gAg 1molAg 107.87gAg =0.81molAg 13gS 1mol S 32.07gS =0.41mol S 2 mol Ag: 1 mol S; Ag 2 S 5

ID: A 76. ANS: 32.07g/mol 100=20.09% S 159.62g/mol 77. ANS: 64.00g/mol 100=31.40% O 203.79g/mol 78. ANS: %Al= 53.96g/mol 100=52.92% Al 101.96g/mol 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 10 23 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 10 23 to determine the number of formula units present. Multiply this result by the number of atoms present in one formula unit of the compound. 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. 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. 6

Study Guide For Chapter 7 [Answer Strip] ID: A D 12. B 27. C 13. A 28. B 1. B 14. B 2. D 15. C 3. A 4. B 16. A 17. D 18. D 5. D 6. C 19. B 20. B 7. B 21. D 22. C 8. C 9. C 23. D 24. D 10. B 25. D 11. D 26.