-.Btoichlometry 67

Exercises

Section 3.2

L An element "E" is present as 10E with a mass value of 10,01 amu, and as 11E with a mass value of 11.01amu. The natural abundances of 10E and UE are 19.78% and 80.22% respectively. What is the averageatomic mass of the element? What is the element?

2. Naturally occurring sulfur consists of four isotopes, 32S (95.0%), 33S (0.76%), 34S (4.22%), and 36S(0.014%). Using these data, calculate the atomic weight of naturally occurring sulfur. The masses of theisotopes are given in the table below.

Atomic mass(amu)

31.9732.9733.9735.97

3. An unknown sample of mystery element "T" is injected into the mass spectrometer. According to the massspectrum, 7.42% of the element is present as 6T, and 92.58% is present as 7T. The mass values are 6.02amu for 6T and 7.02 amu for 7T, Calculate the average atomic mass, and identify the mystery element.

4. A noble gas consists of three isotopes of masses 19.99 amu, 20.99 amu, and 21.99 amu. The relativeabundance of these isotopes is 90.92%, 0,257%, and 8.82% respectively. What is the average atomic massof this noble gas? What noble gas is this?

5. Chlorine has two stable isotopes. The mass of one isotope is 34.97 amu. Its relative abundance is75,53%. What is the mass of the other stable isotope?

6. Complete the following table of isotopic information for the element neon (Ne).

Mass (amu) Abundance19.99 .20,99 0,257%21.99

7. Silicon has three stable isotopes in nature as shown in the table below. Fill in the missing information.

Mass (amu) Abundance27.98

4,70%29.97 3.09%

8, Gallium has two stable isotopes of masses 68.93 amu (69Ga) and 70,92 amu (71Ga), What are the relativeabundances of the two isotopes?

9. Magnesium exists as three isotopes in nature. One isotope (25Mg) has a mass of 24.99 amu and a relativeabundance of 10.13%. The other two isotopes have masses of 23.99 amu (24Mg) and 25.98 amu (26Mg),What are their relative abundances? (atomic mass Mg = 24.305 amu)

68 Chapter 3

10, An element "X" has 5 major isotopes, listed below along with their abundances. What is the element?Does the atomic mass that you calculate based on these data agree with that listed in your periodic table?

Isotope46'X7X8X

X

% "Natural Abundance8.0%7.3%73.8%5.5%5.4%

Atomic Mass45.95269

46.95176447,94794748.94784149.944792

Section 3.3

11. How many moles are in a sample of 300 atoms of nitrogen? How many grams?

12. How many atoms of gold does it take to make 1 gram of gold?

13. If you buy 38.9 moles of M&M's®, how many M&M's® do you have? (1 mole of M&M's* = 6.022 x 1023

M&M's®)

14. A sample of sulfur has a mass of 5.37 g. How many moles are in the sample? How many atoms?

15. Give the number of moles of each element present in 1.0 mole of each of the following substances:

a. Hg2I2

b. LiHc. PbC03

cL Ba3(As04)2

e. RbOH-2H20f. H2SiF6

16. How many grams of zinc are in 1.16 x 1022 atoms of zinc?

17. How many amu are in 3.68 moles of iron?

Section 3.4

18. Calculate the molar masses of each of the following:

c. Ci0H160d. Zr(Se03)2

e. Ca2Fe(CN)6-12H20f. Cr4(P207)3

a. Cu2S04

b. NH4OH

19. Calculate the molar mass of

a. Zn(CN)4

b. Cu(NH3)4-8H20

20. What is the mass of 4.28 x 1022 molecules of water?

21. What is the mass of 4.89 x 1023 atoms of the element "X" described in problem # 10?

22. How many milligrams of Br2 are in 4.8 x 1020 molecules of Br2?

23. How many sodium ions are present in each of the following:

a. 2 moles of sodium phosphateb. 5.8 grams of sodium chloridec. a mixture containing 14.2 grams of sodium sulfate and 2.9 grams of sodium chloride?

Stoichiometry 69

94, How many potassium ions are present in each of the following:

a, 3 moles of potassium chlorideb, 6.2 grams of potassium nitratec, a mixture containing 12.6 grams of potassium phosphate and 5.4 grams of potassium chloride?

25. What is the weight in grams of

a. 0.4 moles of CH4

b. 11 moles of S042~c. 5molesofMg(OH)2?

26. Determine the molar mass of KA1(SO.4)2'12H20.

27. How many moles of cadmium bromide, CdBr2, are in a 39.25 g sample?

28. A sample of calcium chloride, CaCl2, has a mass of 23.8 g. How many moles of calcium chloride is this?

29. If 0.172 moles of baking soda, NaHCO3, were used to bake a chocolate cherry cake, how many grams ofbaking soda would the recipe call for?

30. How many moles are there in a sample of barium sulfate, BaS04, weighing 9,90 x 10"7 g?

31. How many grams are there in 0,36 moles of cobalt (III) acetate, Co(C2H302)3? How many grams of cobaltare in this sample? How many atoms of cobalt?

32. How many milligrams of chlorine are there in a sample of 3,9 x 1019 molecules of chlorine gas, C12? Howmany atoms of chlorine?

33. Bauxite, the principle ore used in the production of aluminum cans, has a molecular formula ofA1203-2H2O.

a. Determine the molar mass of bauxite.b. How many grams of Al are in 0.58 moles of bauxite?c. How many atoms of Al are in 0.58 moles of bauxite?d. What is the mass in grams of 2.1 x 1024 formula units of bauxite?

Section 3.6

34. Calculate the mass percent of Cl in each of the following compounds:

a. GIF c. CuCl2

b. HC1O2 d. PuOCl

35. Calculate the mass percent of each element in C5Hi00.

36. Calculate the mass percent of each element in potassium ferricyanide, K3Fe(CN)6.

37. Calculate the mass percent of each element in barium sulfite, BaSO3.

38. Calculate the mass percent of each element in natural lucite, KAlSi2O6.

39. Calculate the mass percent of silver in each of the following compounds:

a. AgCl b. AgCN c. AgNO3

Chapter 3

40 Chlorophyll a is essential for photosynthesis. It contains 2.72% magnesium by mass What is the molarmass of chlorophyll a assuming there is one atom of magnesium in every molecule of chlorophyll a?

41. Calculate the mass percent of each of the elements in Nicotine, C10H14N2.

Section 3.7

42. Which of the following formulas can be empirical?

a. CH4 d. N205 g. Sb2S3

b> CH2 e« B2H6 h. N204

c. KMn04 f. NH4C1 i. CH2O

43. Determine the empirical and molecular formulas of a compound that has a mass of 3 1.04 g/mole andcontains the following percentages of elements by mass:

C- 38.66%, H = 16.24%, N = 45.10%

44. The analysis of a rocket fuel showed that it contained 87.4% nitrogen and 12.6% hydrogen by weightMass spectral analysis showed the fuel to have a molar mass of 32.05 grams. What are the empirical andmolecular formulas of the fuel?

45. A compound is found, by mass spectral analysis, to contain the following percentages of elements by mass:

C = 49.67%, Cl = 48,92%, H=1.39%

The molar mass of the compound is 289.9 g/mole. Determine the empirical and molecular formula of thecompound.

46. Vanillin, the pleasant smelling ingredient used to bake chocolate chip cookies, is often used in theproduction of vanilla extract. Vanillin has a mass of 152.08 g/mole and contains the following percentagesof elements by mass:

C = 63.18%, H = 5,26%, 0 = 31.56%

Determine the empirical and molecular formula of vanillin.

47. Determine the empirical formula of a compound that contains the following percentages of elements bymass:

Mo = 43.95%, O = 7.33%, Cl = 48,72%

48. A molecule with a molecular weight of approximately 1 10 g/mole is analyzed. The results show that itcontains 10.05% of carbon, 0.84% of hydrogen, and 89.10% of chloride. Calculate the molecular formulaof this compound.

49. Using the data provided, calculate the empirical formulas for the compounds indicated:

a. an oxide of nitrogen, a sample of which contains 6.35 g of nitrogen and 3.65 g of oxygenb. an oxide of copper, one gram of which contains 0,7989 g of copperc. an oxide of carbon that contains 42.84% carbond. a compound of potassium, chloride, and oxygen containing K = 3 1 .97%, 0 = 39.34%e. a compound of hydrogen, carbon, and nitrogen containing H = 3.70%, C = 44.44%, and N = 5 1 .85%.

Stoichfometry 71

Section 3.8

50. How many grams of product are formed in each of the'following reactions?

a. Two moles of H2 react with one mole o£0^ .b. One mole of silver nitrate reacts with one mole of sodium chloride.c. Three moles of sodium hydroxide react with one mole of phosphoric acid.

51 * The following reaction was performed:

Fe203(s) X203(,s)

It was found that 79.847 g of Fe203 reacted with "X" to form 55.847 g of Fe and 50.982 g of X2O3.Identify element X.

52. Do these equations follow the conservation of matter?

IV ~Ka2SiO3.+ 6HF -> SiF4 + 2NaF + 3H202.. 3N2O4 + 2H20 -> 4HNO3 + 2N02

Section 3,9

'53. Fill in the blanks to balance the following chemical equations:

a. Agl + Na2S -* . Ag2S + Nal

b/ ,(NH4)2Cr2O7 -+ Cr2O3 + __N2 + H20

c. _Na3P04 + HC1 -> NaCl*, H3PO4

d. . TiCU + H2O -» Ti02 + HC1

e. __Ba3N2 + H2O -> Ba(OH)2 + NH3

f. __HNO2 -* HN03 + NO + H20

54. Balance the following equation:

_NH4OH(/) + _KA1(SO4)2-12H20 -^ _,

55. Balance the following equation:

56. Complete the following reactions (making sure they are balanced):

a. HN03 + ____ -» H20 + KNO3

b. + Na3P04 ~> Ca3(P04)2 + NaCl

c. Mg(OH)2 + HC1 -* MgCl2 +

d. + C12 -t NaCl 4 Br2

57, Balance the followrng equations:

a; _Ca + C

ti. FeS + C

c. HNO2 -*

H20(/)

. _ H2(g)

O

i2 -4

N02

;Fe203 +

. CaC03

__S02

NO

d. PCI, + H,0 HC1

72 Chapter 3

Section 3.10

58, How many grams of water vapor can be generated from the combustion of 1 8.74 g of ethanol?

C2H60(g) + 02(g) -* C02(g) + H20(g) (unbalanced)

59. How many grams of sodium hydroxide are required to form 5 1 .63 g of lead hydroxide?

Pb(NO3)2(ff<gO + NaOH(a^) -* Pb(OH)2(s) + NaN03(a<gO (unbalanced)

60. How many grams of potassium iodide are necessary to completely react with 20,61 g of mercury (II)chloride?

HgCl2(ff<20 + Kl(aq) -> HgI2 + KCl(aq) (unbalanced)

61. How many grams of oxygen are necessary to completely react with 22,8 grams of methane, CH4? (Pleasewrite the entire reaction,)

62. If, in the previous problem, only 25.9 grams of water vapor were formed, how much methane actuallyreacted with oxygen?

63. What mass of calcium carbonate (CaC03) would be formed if 248.6 g of carbon dioxide (C02) wereexhaled into limewater, Ca(OH)2? How many grams of calcium would be needed to form that amount ofcalcium carbonate? Assume 100% yield in each reaction.

64. The following reaction is used to form lead iodide crystals. What mass of crystal (PbI2) could be formedfrom 1 .0 x 1 03 g of lead (II) acetate [Pb(C2H302)2]?

Pb(C2H302)2(<7<7) + 2KI(a<?) -+ PbI2(s) + 2KC2H302(a<7)

65. How many grams of precipitate (Hg2Cl2) would be formed from a solution containing 102.9 g of mercuryions that are reacted with chloride ions as follows?

66. You were hired by a laboratory to recycle 6 moles of silver ions. You were given 150 g of copper. Howmany grams of silver can you recover? Is this enough copper to recycle 6 moles of silver ions?

2Ag+ + Cu -» 2Ag + Cu2+

67. Fermentation converts sugar into ethanol and carbon dioxide. If you were to ferment a bushel of applescontaining 235 g of sugar, what is the maximum amount of ethanol in grams that would be produced?

C6H1206 -> 2C2H60 + 2C02

68. The reaction between potassium chlorate and red phosphorus is highly exothermic and takes place whenyou strike a match on a matchbox. If you were to react 52.9 g of potassium chlorate (KC1O3) with redphosphorus, how many grams of tetraphosphorus decaoxide (P^io) would be produced?

KClO3(,s) + P4(<0 -* P4OioG?) + KCl(s) (unbalanced)

Section 3.11

69. A reaction combines 133.484 g of lead(II) nitrate with 45.010 g of sodium hydroxide (see problem 59).

a. How much lead(II) hydroxide is formed?b. Which reactant is limiting? Which is in excess?c. How much of the excess reactant is left over?d. If the actual yield of lead(II) hydroxide were 80.02 g, what was the percent yield?

Stoic^iometry

70. A reaction combines 64.81 grams of silver nitrate with 92.67 grams of potassium bromide.

73

a. How much silver bromide is formed?b. Which reactant is limiting? Which is in excess?c. How much of the excess reactant is left over?d. If the actual yield of silver bromide were 14.77 g, what was the percent yield?

71. A reaction proceeds between 94.6 g of KC103 and 65.3 g of P4 (see problem 68).

a. How much potassium chloride is formed?b. Which reactant is limiting? Which is in excess?c. How much of the excess reactant is left over?d. If the actual yield of potassium chloride were 21.0 g, what was the percent yield?

72. DDT, an insecticide harmful to fish, birds, and humans, is produced by the following reaction:

2C6H5C1 + C2HOC13

chlorobenzene chloralC14H9C15 + H2

DDT

In a government lab 1142 g of chlorobenzene were reacted with 485 g of chloral.

a. How much DDT is formed?b. Which reactant is limiting? Which is in excess?c. How much of the excess reactant is left over?d. If the actual yield of DDT were 200.0 g, what was the percent yield?

Multiple Choice Questions

73. Which one of the following elements has been selected as the current atomic weight standard?

A. 0 B, C C. H D. Na

74. Bromine is composed of two isotopes. One of the isotopes, Br-xx.x, makes up 49.7% of the total, whilethe other, Br-78.9, makes up 503% of the total. Calculate the atomic mass of Br-xx.x.

A, 80,0 B. 80.9 C. 89.7 D. 78.9

75. How many years would 1.0 mole of seconds make up? Do not consider leap years.

A. 1,9x10" B. 1.1x10" C. 3.0 x lO 4 D. 3.5x1017

76. How many neutrons are present in 50 atoms of chlorine that have a 50-50 mixture of Cl-35 and Cl-37?

A. 38 B. 1.7 x l O 3 C. 8x l0 2 D. 9.5 x lO 2

77. Four beakers containing potassium nitrate dissolved in water are allowed to evaporate to dryness. Beakers1 through 4 contain 2.3, 1.91, 5.985, and 0.52 g of dry potassium nitrate respectively. How many moles ofpotassium nitrate were recovered after the water evaporated?

A. 0.106 B, 0.212 C. 0.500 D. 2.35

78. How many atoms of uranium (U) are present in 1 nanogram of uranium?

A. 2.5 x l O 2 B. 5.0x1010 C. 2.5x10' D. 5.0x1030

74 Chapter 3

79. Water has a density of 1.00 g/cnr . How many moles of water are present in / 2 cup of water? 4 cups =I q t .

A. 2.0 B. 3.05 C. 0.65 D. 6.65

80. Calculate how many moles of electrons are found in 401.4 g of P .

A. 194 B. 402 C. 154 D. 233.2

81. 18.0 cm3 water (assume density 1.00 g/cnr') contains 1.0 moles of water molecules. If a beaker containing0.9 cm3 of water is allowed to evaporate over a period of 24 hours, how many molecules of waterevaporate per second? Assume a constant rate of evaporation.

A. 7 .0x10 ' B. 1 . 5 x l 0 2 3 C. 3.Ox 1023 D. 3 .5x10 '

82. Calculate the percent composition of Na2S2O3.

A. 29%Na,41%S,30%OB. 37% Na, 45% S, 23% O

C. 49% Na, 34% S, 17%OD. 17%Na, 47% S, 36% O

83. Calculate the percent composition of hydrogen in sucrose (C!2H22Oi ]).

A. 6% B. 10% C. 33% D. 20%

84. Two of the three forms of vitamin B6 are pyridoxine (C8Hi |NO2) and pyridoxamine (C8Hi2N2O).Calculate the respective percentage of nitrogen in each compound.

A. 8.8%, 17% B. 9.3%, 18% C. 9.2%, 17% D. 18%, 9.2%

85. Calculate the molecular formula of a compound that has 48.8% Cd, 20.8% C, 2.62 % H, 27.8 % O, and amolecular weight of 460.8 g/mol.

A. Cd.CgHpO. B. CdC4H604 C. CdCHO D. Cd2C6H6O6

86. Determine the molecular formula of a compound that contains 26.7% P, 12.1% N, 61.2% Cl, and amolecular weight of 580 g/mol.

A. (PNC1)3 B. (PNC12)5 C. (P2NC12)5 D. PNC1-,

87. Calculate the empirical formula for a compound that contains 32.2% Ca and 67.8% N by mass.

A. Ca(N3)2 B. CaN2 C. CaN D. CaN4

88. A 20 mg sample of CxHy is burned in oxygen to produce 60 mg of carbon dioxide and 32 mg of water.Calculate x and y by using these data.

A. 2,4 B. 3,6 C. 1,4 D. 3,8

89. Find the empirical formula of the compound that contains 15.8% Al, 28.1 % S, and 56.1% O.

A. A12(SO4)3 B. A1SO2 C. A1SO D. A12SO3

90. Find the identity of the element X in the following equation

C3H6X3 + 3X2 -» 3CX2 4- 3H2O

A. O B. H C. Cl D. Br

91. 505 grams of KOH are required to completely react with 4.50 moles of sulfuric acid. How many moles ofproducts are produced8?

A. 9 moles B. 4.50 moles C. 13.5 moles D. 5.50 moles

Stoichiometry 75

92, The proper set of coefficients for the following equation are

_C3H60 3 + __02 -> _C02 + _H20

A. 1,3,3,3 B. 2,4,3,3 C. 1,2,3,3 D. 1,6,6,6

93, The proper set of coefficients for the following equation are

_AgCl + _HN03 -> _AgN03 + _HCl

A, 1,1,1,1 B. 1,2,2,1 C, 2,3,1,1 D. 2,2,2,2

94, The proper set of coefficients for the following equation are

_C3H8 + _F2 -» _C3F8 + _HF

A. 1,1,1,1 B. 1,3,1,3 C. 2,16,2,16 D. 1,8,1,8

95, For every liter of sea water that evaporates, 3,7 g of magnesium hydroxide are produced. How many litersof sea water must evaporate to produce 5,00 moles of magnesium hydroxide?

A, 78.4 B, 50 C. 143 D, 18,5

96, A solution of copper sulfate is treated with zinc metal. How many grams of copper are produced if 2.9 gof zinc are consumed? .

A. 2.9 g

CuS04

B. 2.8 g

ZnSO4+Cu

C. 5,7 g D. 3,7 g

97. How many grams of carbon dioxide are produced from the burning of 1368 g of sucrose according to thefollowing equation?

Ci2H22On + 1202 -* 12C02 + 11H20

A, 342 g B. 176 g C. 1056 g D. 211 I g

98. How many grams of sulfur dioxide are produced when 90.0 g of thionyl chloride reacts with excess wateraccording to the following equation?

SOC12 + H2O -+2HC1 + S02

A, 96.8 B. 90.0 C. 24,2 D. 48,5

99. Calcium oxide is a basic oxide that is not very soluble in water solutions, Calcium oxide can react withcarbon dioxide to form calcium carbonate (according to the equation below). Calcium carbonate is aninsoluble salt that forms stalactites and stalagmites, How many moles of carbon dioxide are removed fromwater if a 400.0 Ib stalagmite is formed?

CaO + CO2 -» CaCO3

A. 1813 B. 908 C. 4000 D. 2258

100. Calculate the number of grains of TIOC12 required to react with 134 g of carbon.

2TiOGl2> 2C -> 2Ti + C02 + CCU

A, 134 B. 1.51 x lO 3 C. 536 D, 67

101. Calculate the number of grams, of methane (CH4) required to react with 25.0 g of chlorine according to thefollowing equation: '

3 CH4 + 4C12 -* 2CH3C1 + CH2C12 + 4HC1

A. 33.3 B. 18,8 ' C. 2.11 D. 4.23

Chapter 3

IQ2. Identify the limiting reagent and calculate the number, of grams left over in excess for the;i)Howingequation:

Cr203 + 3CCl4 -H-2CrCI3 + 3GOCK

The reaction began with 5.00 g of Cr203 and 12.0 g of CC14. '

A. Limiting:. CC14, 1.05 g Cr203 left overB. Limiting: Cr2O3, 10.0 g CC14 left over

C. Limiting: CCU, 3.70 gCr203 leftoverD. Limiting: Cr2O3, 6.75 g CC14 left over

103, Identify the limiting reagent and the number of grams left over in excess if L9 grams each of phosgene andsodium hydroxide are combined in the following reaction:

COCU + 2NaOH -* 2NaCl + H->O + CO-)

A. Limiting: COC12, 0.588 g NaOH left overB. Limiting: COC12, 0,4 g NaOH left over

C. Limiting: NaOH, 0.520 g COC12 left overD. Limiting: NaOH, 0.355 g COC12 left over