Quantities in Chemistry

Chapter 6 Quantities in Chemistry

Multiple Choice:

1. Given that the mass of one beryllium atom is 9.01 amu and that of one bromine atom is 79.90 amu, what is the mass ratio of beryllium to bromine? a. 9.01 : 79.90 b. 79.90 : 9.01 c. 9.01 x 79.90 d. 79.90 x 9.01

2. The mass ratio is applicable to a. units of grams. b. units of amu. c. any units of mass. d. any units of moles.

3. How many grams of oxygen are combined with 75.0 grams of iron to make the iron(II) oxide compound? a. 262 g b. 16.0 g c. 11.9 g d. 21.5 g

4. How many grams of iron are combined with 75.0 grams of oxygen to make the iron(II) oxide compound? a. 21.5 g b. 11.9 g c. 262 g d. 21.4 g

5. How many pounds of oxygen are combined with 221 lbs of iron to make the iron(III) oxide compound? a. 514 lbs b. 95.0 lbs c. 24.3 lbs d. 243 lbs

6. How many pounds of iron are combined with 221 lbs of oxygen to make the iron(III) oxide compound? a. 514 lbs. b. 95.0 lbs c. 243 lbs d. 24.3 lbs

73 7. What is the mass ratio for the elements in aluminum chloride (AlCl3)? [Al:Cl] a. 27:35.5 b. 27:106.5 c. 0.4:1.0 d. 3.9:1.0

8. What is the mass ratio for the elements in dinitrogen trioxide (N2O3)? [N:O] a. 14:16 b. 7:8 c. 48:28 d. 7:12

9. If 23.6 g of Na and 23.6 g of I combine to form NaI, how much of which element will be leftover after the reaction? a. I – 130. g b. Na – 4.28 g c. Na – 19.3 g d. I – 106 g

10. If 4.5 g of Zn and 45.0 g of O combine to form ZnO, how much of which element will be leftover after the reaction? a. Zn – 184 g b. Zn – 180 g c. O – 44 g d. O – 1.1 g

11. The value associated with a mole is based on which one of the following isotopes? a. 13C b. 16O c. 24Cr d. 12C

12. Having one mole of carbon dioxide means that you have 23 a. 6.022x10 moles of carbon 23 b. 6.022x10 atoms of oxygen 23 c. 6.022x10 molecules of CO2 d. 1 molecule of CO2

13. Having one mole of carbon dioxide means that you have 23 a. 6.022x10 moles of carbon 23 b. 6.022x10 atoms of oxygen c. 1 mole of carbon atoms d. 1 molecule of CO2

74 14. The concept of the mole is analogous to which one of the following common “concepts”? a. a gaggle of geese b. a buffalo herd c. a ream of paper d. a load of laundry

15. Which one of the following is not a good example to describe the concept of a mole? a. a herd of elephants b. a dozen eggs c. a 24-pack of soda d. a ream of paper

16. Determine the number of moles in a 15.4-g sample of zinc. a. 0.2355 moles b. 0.236 moles c. 1007 moles 3 d. 1.00x10 moles

-6 -4 17. You have already determined that there are 3.33x10 moles in 2.92x10 grams of strontium. How many atoms of strontium are in this sample? 18 a. 2.01x10 atoms 20 b. 1.76x10 atoms -21 c. 5.68x10 atoms -19 d. 4.98x10 atoms

18. How many moles are in 23.0 g of Na? a. 1.0 moles b. 23.0 moles c. 0.0435 moles 23 d. 6.022 x 10 moles

19. How many moles are in 183.85 g of W? a. 183.85 moles b. 0.00544 moles c. 1.00 moles 23 d. 6.022 x 10 moles

20. What is the mass of 0.50 moles of Li? a. 3.5g b. 14 g c. 0.072 g d. 7.0 g

21. What is the mass of 4.3 moles of Se?

75 a. 340 g b. 18 g 24 c. 2.6 x 10 g -24 d. 7.1 x 10 g

18 22. A sample of plutonium is known to contain 4.5x10 atoms. How many moles of plutonium are present? 21 a. 1.08x10 moles -22 b. 9.30x10 moles 5 c. 1.34x10 moles -6 d. 7.47x10 moles

23. If a sample of cobalt is composed of 3.231 moles, what is its mass? a. 190 g b. 0.0548 g c. 196 g 24 d. 1.95x10 g

24. What is the mass of one mole of chlorine? a. 35.45 g b. 70.90 g c. 17.72 g d. not enough information

25. How many moles are in 34.9 g of Ni? a. 1.00 mole 25 b. 2.10 x 10 moles c. 0.595 moles d. 2050 moles

26. How many moles are in 555 g of Sr? 4 a. 4.86 x 10 moles 26 b. 3.34 x 10 moles c. 6.33 moles -22 d. 9.22 x 10 moles

27. What is the formula weight for iron(III) oxide? a. 183.6 amu b. 199.6 amu c. 143.7 amu d. 159.7 amu

28. How many atoms are contained in a 13.3-g sample of titanium (Ti)? 24 a. 8.01x10 26 b. 3.83x10 23 c. 1.67x10

76 24 d. 2.17x10

29. What is the formula weight for barium phosphate, Ba3(PO4)2? a. 232.3 amu b. 507.0 amu c. 602.0 amu d. 559.6 amu

30. What is the atomic mass for capsaicin (C18H27NO3), which is responsible for the heat of a chili pepper? a. 291.4 amu b. 305.5 amu c. 49.0 amu d. 367.0 amu

. 31. Determine the formula weight for cobalt(II) chloride hexahydrate (CoCl2 6H2O).

a. 112.4 amu b. 238.0 amu c. 147.8 amu d. 202.5 amu

24 32. A sample of N2O5 is known to contain 4.3x10 molecules. How many nitrogen atoms are in this sample? 24 a. 4.3x10 atoms 24 b. 8.6x10 atoms 48 c. 4.3x10 atoms 25 d. 2.2x10 atoms

24 33. A sample of N2O5 is known to contain 4.3x10 atoms of nitrogen. How many oxygen atoms are in this sample? 24 a. 4.3x10 atoms 25 b. 1.1x10 atoms 24 c. 1.7x10 atoms d. 7.1 atoms

24 34. A sample of N2O5 is known to contain 4.3x10 molecules. What is the mass of this sample? a. 770 g b. 0.066 g 50 c. 2.8x10 g d. 210 g

35. Monoclinic sulfur (S8) is used in the vulcanization of rubber and in the making of gunpowder. How many moles of sulfur are there in 17.62 g of S8? a. 244.3 mol b. 14.56 mol

77 c. 0.0687 mol d. 0.550

36. Used in the manufacture of rat poisons, white phosphorus exists as cubic crystals -3 containing P4 molecules. What is the mass of 6.431 x 10 mol of P4? a. 0.1992 g -4 b. 2.077 x 10 g c. 0.04979 g d. 0.7967 g

37. When converting from moles of nitrate ion to moles of aluminum in aluminum nitrate, which of the below mole ratios should be utilized? - a. 1 mole of Al/3 mole NO3 - b. 3 mole NO3 /1 mole of Al - c. 2 mole of Al /3 mole NO3 - d. 3 mole of Al /2 mole NO3

38. When converting from moles of carbon to moles of oxygen in C9H11FN2O5, which of the below ratios should be utilized? a. 9 mole C/5 mole O b. 5 mole O/28 mole compound c. 5 mole O/9 mole C d. 1 mole O/1 mole C

39. What is the mass of 0.00322 moles of Na2SO4? a. 0.229 g b. 0.457 g 4 c. 4.41x10 g d. 0.395 g

40. The following mole ratio is used to convert from moles of barium to moles of oxygen, (6 mole O/1 mole Ba). For which chemical compound is this ratio applicable? a. Ba(NO3)2 b. BaO c. BaSO3 d. Ba(ClO4)2

41. The following mole ratio is used to convert from moles of sodium to moles of oxygen, (1 mole O/1 mole Na). For which chemical compound is this ratio applicable? a. Na2O b. NaNO3 c. Na3PO3 d. none of the above

78 42. The following mole ratio is used to convert from moles of oxygen to moles of nitrogen, (1 mole N/3 mole O). This ratio applies to which compound? a. N2O5 b. Ba(NO3)2 c. KNO2 d. C12H12N2O2S

43. A sample of nitrogen gas has a mass of 23.3 g. How many moles of nitrogen are in this sample? a. 1.66 mol b. 326 mol c. 0.832 mol d. 653 mol

44. A sample of dinitrogen tetraoxide has a mass of 1.5 g. How many moles of oxygen are present in this sample? a. 0.016 mol b. 0.326 mol c. 0.023 mol d. 0.065 mol

45. A sample of dinitrogen trioxide contains 0.25 moles of oxygen. How many moles of compound are present? a. 0.25 mol b. 0.75 mol c. 0.083 mol d. 0.50 mol

46. A sample of dinitrogen trioxide contains 0.25 moles of oxygen. How many molecules of the compound are present? 23 a. 1.5x10 molecules 23 b. 4.5x10 molecules 22 c. 5.0x10 molecules 23 d. 3.0x10 molecules

21 47. A sample of Fe2O3 contains 5.4x10 atoms of oxygen. What is its mass? a. 1.4 g b. 0.48 g c. 2.2 g d. 0.96 g

48. A sample of Cr2O3 has a mass of 0.33 g. How many chromium atoms are in this sample? 21 a. 3.9x10 atoms 25 b. 9.1x10 atoms 21 c. 1.3x10 atoms

79 21 d. 2.6x10 atoms

49. What is the percent composition of chlorine in the compound Ba(ClO3)2? a. 23.3% b. 11.7% c. 18.8% d. 16.1%

50. What is the percent composition of barium in the compound Ba(ClO3)2? a. 62.2% b. 82.3% c. 45.1% d. 57.2%

51. What is the percent composition of oxygen in the compound Ba(ClO3)2? a. 31.6% b. 15.8% c. 5.26% d. 21.7%

52. A compound contains 0.35 moles of nitrogen and 0.52 moles of oxygen. What is the empirical formula? a. NO2 b. N2O3 c. N2O5 d. NO

53. The simplest whole-numbered ratio of atoms in a compound is known as the a. molecular formula. b. chemical formula. c. molecular equation. d. empirical formula.

54. The molar mass of one empirical unit of the antidepressant rolicyprine (C7H8NO) is 122.1 g/empirical unit. If the molar mass for rolicyprine is approximately 250 g/mol, how many empirical units are present in each molecular unit? a. 1 b. 2 c. 3 d. 0.5

55. The empirical formula for -cyclodextrin, which is used in the study of the

activities of enzymes, is C6H10O5. If the molar mass for -cyclodextrin is approximately 1300 g/mol, how many empirical units are present in each molecular unit? a. 4

80 b. 6 c. 8 d. 10

Short Answer:

56. (T/F) One mole of silver atoms has a mass of 107.87 g.

23 57. (T/F) Analogous to there being 24 cans of soda in a case, there is 6.022x10 of anything in a mole.

58. (T/F) For every mole of lithium carbonate, there is one mole of lithium atoms.

59. (T/F) The molecular formula for a compound is always presented in the smallest whole-numbered ratio.

60. (T/F) The mass ratio between elements in a compound is the same regardless of the units.

61. (T/F) The mass ratio between C and Cl (C:Cl) in the molecule CH2Cl2 is 5.9:1.

62. (T/F) In order to make BF3, you need to combine 19.00 lbs of F with 10.81 lbs of B.

63. (T/F) The mole is defined as the number of atoms in exactly 12 grams of matter.

12 64. (T/F) 12 g of C contains 6.022x1023 atoms of carbon.

65. (T/F) Hydrated ionic compounds are compounds that have all of the water molecules vaporized out of the sample.

66. (T/F) The percent composition of Cu in a sample of copper(II) bromide (CuBr2) is 28.5%.

67. A bored chemistry professor counts the blades of grass in a 1.0 sq. ft. section of his yard. In this section of the yard, the professor counts 2400 blades of grass. Assuming that there is a uniform distribution of grass throughout the yard, how many blades of grass are in the yard if it occupies an area of 7500 square feet?

Answer:

68. Using your answer to the above problem, how many moles of blades of grass are in the yard?

Answer:

81 69. If 45.0 g of Al and 45.0 g of O combine to form Al2O3, would you use all of the reactants? If not, how much of the excess element would be leftover?

Answer:

70. If 32.4 g of Cu and 18.1 g of Cl combine to form CuCl, would you use all of the reactants? If not, how much of the excess element will be leftover?

Answer:

71. Does the chemical composition of a compound tell us anything about the compound’s chemical behavior?

Answer:

72. Discuss the relationship between an empirical formula and a molecular formula.

Answer:

73. Lindane is the trade name for an insecticide that has been used successfully against certain DDT-resistant insects. It is composed of 24.78% carbon, 1.05% hydrogen, and 74.17% chlorine. Determine the molecular formula for Lindane if its molar mass is 291 g/mol. Arrange the chemical formula for Lindane as CHCl.

Answer:

74. Determine the empirical formula for a compound composed of 68.4% Cr and 32.6% O.

Answer:

75. Determine the empirical formula for a compound composed of 20.7% O and 79.3% W.

Answer:

76. Agroclavine is composed of 80.6% C, 7.6% H, and 11.8% N. Determine the empirical formula for this compound. If the molar mass for the compound is 238.3 g/mol, determine its molecular formula.

Answer:

82 77. A sample of streptidine contains 36.64% C, 6.92% H, 32.04% N, and 24.40% O. Determine the empirical formula for this compound. If the molar mass of the compound is 262.27 g/mol, determine its molecular formula.

Answer:

78. Given the following empirical formula for streptidine (C4H9N3O2), address the following questions: a. If the molar mass of streptidine is 262.27 g/mol, what is its molecular formula? b. How many molecules of streptidine are present in a 0.235-g sample of the compound? c. How many atoms of N are in this same sample? d. How many grams of C are in this same sample?

Answer:

79. Phenolphthalein, an organic dye used to indicate the endpoint in acid-base titrations, has a molar mass of 320.34 g/mol. It is composed of 74.99% C, 5.03% H, and 19.98% O. What is the molecular formula for phenolphthalein?

Answer:

80. The empirical formula for sodium dithionate is NaO3S. Based on the empirical formula, address the following questions. a. If the molar mass of the compound is 206.11 g/mol, what is the molecular formula of sodium dithionate? b. What is the percent composition of Na in the compound? c. What is the mass ratio between O and S (O:S) in the compound? 22 d. What is the mass, in grams, of 2.3x10 formula units of this compound? e. How many atoms of S are in a 2.35-g sample of the compound?

Answer: