Medgar Evers College Preparatory School Science Department
Chemistry II Ms. Parker
Unit VI: Stoichiometry Problem Set
Part I: Multiple Choice. Write an answer and a one-sentence explanation
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1. Given the balanced equation with an unknown compound represented by X:
C6H12O6(aq) 2X + 2CO2(g)
Which compound is represented by X?
(1) CH3OH(aq)
(2) CH2(OH)4(aq)
(3) CH3CH2OH(aq)
(4) CH2OHCH2OH(aq)
2. Given the incomplete equation for the combustion of ethane:
2C2H6 + 7O2 → 4CO2 + 6 ____
What is the formula of the missing product?
(1) CH3OH (3) H2O
(2) HCOOH (4) H2O2
3. Given the incomplete equation:
4Fe + 3O2 → 2X
Which compound is represented by X?
(1) FeO (3) Fe3O2
(2) Fe2O3 (4) Fe3O4
4. Given the reaction:
PbCl2(aq) + Na2CrO4(aq) → PbCrO4(s) + 2NaCl(aq)
What is the total number of moles of NaCl formed when 2 moles of Na2CrO4 react completely?
(1) 1 mole (3) 3 moles
(2) 2 moles (4) 4 moles
5. Given the reaction:
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O
What is the ratio of moles of CO2 produced to moles of C2H6 consumed?
(1) 1 to 1 (3) 3 to 2
(2) 2 to 1 (4) 7 to 2
6. Given the reaction:
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O
What is the total number of moles of CO2 produced by the complete combustion of 5.0 moles of C2H6?
(1) 1.0 mole (3) 5.0 moles
(2) 2.0 moles (4) 10. moles
7. Given the balanced equation:
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(ℓ) + CO2(g)
What is the total number of moles of CO2 formed when 20. moles of HCl is completely consumed?
(1) 5.0 mol (3) 20. mol
(2) 10. mol (4) 40. mol
8. A sample of a compound contains 65.4 grams of zinc, 12.0 grams of carbon, and 48.0 grams of oxygen. What is the mole ratio of zinc to carbon to oxygen in this compound?
(1) 1:1:2 (3) 1:4:6
(2) 1:1:3 (4) 5:1:4
9. Given the reaction:
6 CO2 + 6 H2O → C6H12O6 + 6 O2
What is the total number of moles of water needed to make 2.5 moles of C6H12O6?
(1) 2.5 (3) 12
(2) 6.0 (4) 15
10. Given the equation:
2C2H2 (g) + 5O2 (g) → 4 CO2 (g) + 2H2O(g)
How many moles of oxygen are required to react completely with 1.0 mole of C2H2 ?
(1) 2.5 (3) 5.0
(2) 2.0 (4) 10
11. Given the balanced equation representing a reaction:
F2(g) + H2(g) → 2HF(g)
What is the mole ratio of H2(g) to HF(g) in this reaction?
(1) 1:1 (3) 2:1
(2) 1:2 (4) 2:3
12. Given the balanced equation:
2C + 3H2 → C2H6
What is the total number of moles of C that must completely react to produce 2.0 moles of C2H6?
(1) 1.0 mol (3) 3.0 mol
(2) 2.0 mol (4) 4.0 mol
13. Given the balanced equation:
2 C4H10(g) + 13 O2(g) → 8 CO2(g) + 10 H2O(g)
What is the total number of moles of O2(g) that must react completely with 5.00 moles of C4H10(g)?
(1) 10.0 (3) 26.5
(2) 20.0 (4) 32.5
14. Given the reaction:
N2(g) + 3 H2(g) 2 NH3(g)
What is the mole-to-mole ratio between nitrogen gas and hydrogen gas?
(1) 1:2 (3) 2:2
(2) 1:3 (4) 2:3
15. Which equation shows a conservation of mass?
(1) Na + Cl2 → NaCl
(2) Al + Br2 → AlBr3
(3) H2O → H2 + O2
(4) PCl5 → PCl3 + Cl2
16. Given the balanced equation:
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s)
This reaction is classified as
(1) synthesis
(2) decomposition
(3) single replacement
(4) double replacement
17. Given the balanced equation:
2KClO3 → 2KCl + 3O2
Which type of reaction is represented by this equation?
(1) synthesis
(2) decomposition
(3) single replacement
(4) double replacement
18. Which list includes three types of chemical reactions?
(1) condensation, double replacement, and sublimation
(2) condensation, solidification, and synthesis
(3) decomposition, double replacement, and synthesis
(4) decomposition, solidification, and sublimation
19. Which equation represents a double replacement reaction?
(1) 2 Na + 2 H2O → 2 NaOH + H2
(2) CaCO3 → CaO + CO2
(3) LiOH + HCl → LiCl + H2O
(4) CH4 + 2 O2 → CO2 + 2 H2O
20. Given the reaction:
Mg(s) + 2 AgNO3(aq) → Mg(NO3)2(aq) + 2 Ag(s)
Which type of reaction is represented?
(1) single replacement (3) synthesis
(2) double replacement (4) decomposition
21. What is the total number of oxygen atoms in the formula MgSO4●7H2O? [The ● represents seven units of H2O attached to one unit of MgSO4]
(1) 11 (3) 5
(2) 7 (4) 4
22. The gram formula mass of NH4Cl is
(1) 22.4 g/mole (3) 53.5 g/mole
(2) 28.0 g/mole (4) 95.5 g/mole
23. A compound has a gram formula mass of 56 grams per mole. What is the molecular formula for this compound?
(1) CH2 (3) C3H6
(2) C2H4 (4) C4H8
24. A substance has an empirical formula of CH2 and a molar mass of 56 grams per mole. The molecular formula for this compound is
(1) CH2 (3) C4H8
(2) C4H6 (4) C8H4
25. What is the empirical formula for the compound C6H12O6?
(1) CH2O (3) C3H6O3
(2) C2H4O2 (4) C6H12O6
26. What is the empirical formula of a compound with the molecula formula N2O4?
(1) NO (3) N2O
(2) NO2 (4) N2O3
27. Which pair of compounds has the same empirical formula?
(1) C2H2 and C6H6
(2) C2H6 and C3H8
(3) CH3OH and C2H5OH
(4) CH3CHO and CH3COOH
28. What is the molecular formula of a compound that has a molecular mass of 54 and the empirical formula C2H3?
(1) C2H3 (3) C6H9
(2) C4H6 (4) C8H12
29. Which is an empirical formula?
(1) P2O5 (3) C2H4
(2) P4O6 (4) C3H6
30. Given the structural formula:
What is the empirical formula of this compound?
(1) CH3O (3) C4H10O2
(2) C2H5O (4) C8H20O4
31. Which pair of formulas correctly represents a molecular formula and its corresponding empirical formula?
(1) C2H2 and CH (3) C4H6 and CH
(2) C3H4 and CH2 (4) C5H8 and C2H2
32. The molecular formula of glucose is C6H12O6. What is the empirical formula of glucose?
(1) CHO (3) C6H12O6
(2) CH2O (4) C12H24O12
33. A sample of a substance containing only magnesium and chlorine was tested in the
laboratory and was found to be composed of 74.5% chlorine by mass. If the total mass of the sample was 190.2 grams, what was the mass of the magnesium?
(1) 24.3 g (3) 70.9 g
(2) 48.5 g (4) 142 g
34. The percent composition by mass of magnesium in MgBr2 (gram-formula mass = 184 grams/mole) is equal to
(1) 24 x 100 (3) 184 x 100
184 24
(2) 160. 100 (4) 184 100
184 160.
35. What is the percent by mass of oxygen in H2SO4 ? [formula mass = 98]
(1) 16% (3) 65%
(2) 33% (4) 98%
36. What is the percent composition by mass of aluminum in Al2(SO4)3 (gram-formula mass = 342 grams/mole)?
(1) 7.89% (3) 20.8%
(2) 15.8% (4) 36.0%
37. The percentage by mass of Br in the compound AlBr3 is closest to
(1) 10.% (3) 75%
(2) 25% (4) 90.%
38. In which compound is the percent by mass of oxygen greatest?
(1) BeO (3) CaO
(2) MgO (4) SrO
39. What is the percent composition by mass of nitrogen in NH4NO3 (gram-formula mass = 80.0 grams/mole)?
(1) 17.5% (3) 52.5%
(2) 35.0% (4) 60.0%
40. A hydrated salt is a solid that includes water molecules within its crystal structure. A student heated a 9.10-gram sample of a hydrated salt to a constant mass of 5.41 grams. What percent by mass of water did the salt contain?
(1) 3.69% (3) 40.5%
(2) 16.8% (4) 59.5%
41. A hydrate is a compound with water molecules incorporated into its crystal structure. In an experiment to find the percent by mass of water in a hydrated compound, the following data were recorded:
Mass of crucible + hydrated crystals before heating / 7.50 gramsMass of crucible / 6.90 grams
Mass of crucible + anhydrous crystals after heating / 7.20 grams
What is the percent by mass of water in the hydrate?
(1) 8.0 % (3) 72. %
(2) 50. % (4) 96. %
42. What is the percent by mass of oxygen in propanal, CH3CH2CHO?
(1) 10.0% (3) 38.1%
(2) 27.6% (4) 62.1%
43. In which compound is the percent composition by mass of chlorine equal to 42%?
(1) HClO (gram-formula mass = 52 g/mol)
(2) HClO2 (gram-formula mass = 68 g/mol)
(3) HClO3 (gram-formula mass = 84 g/mol)
(4) HClO4 (gram-formula mass = 100. g/mol)
44. The percent by mass of hydrogen in NH3 is equal to
(1) 17 x 100 (3) 1 x 100
1 17
(2) 17 x 100 (4) 3 x 100
3 17
45. A hydrate is a compound that includes water molecules within its crystal structure. During an experiment to determine the percent by mass of water in a hydrated crystal, a student found the mass of the hydrated crystal to be 4.10 grams. After heating to constant mass, the mass was 3.70 grams. What is the percent by mass of water in this crystal?
(1) 90.% (3) 9.8%
(2) 11% (4) 0.40%
46. The percent by mass of calcium in the compound calcium sulfate (CaSO4) is approximately
(1) 15% (3) 34%
(2) 29% (4) 47%
47. The data table below gives the temperature and pressure of four different gas samples, each in a 2-liter container.
Temperature and Pressure of Gas Samples
Gas Sample / Temperature (K) / Pressure (atm)He / 300. / 1.20
Ne / 300. / 1.00
CO2 / 200. / 1.20
CH4 / 300. / 1.00
Which two gas samples contain the same total number of particles?
(1) CH4 and CO2 (3) He and CO2
(2) CH4 and Ne (4) He and Ne
48. At 1 atmosphere and 298 K, 1 mole of H2O(ℓ) molecules and 1 mole of C2H5OH(ℓ) molecules both have the same
(1) vapor pressure
(2) average kinetic energy
(3) mass
(4) density
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Part II: Constructed Response
Base your answers to questions 49 and 50 on the information below.
Air bags are an important safety feature in modern automobiles. An air bag is inflated in milliseconds by the explosive decomposition of NaN3(s). The decomposition reaction produces N2(g), as well as Na(s), according to the unbalanced equation below.
NaN3(s) → Na(s) + N2(g)
49. Balance the equation in your answer booklet for the decomposition of NaN3, using the smallest whole-number coefficients. [1]
50. When the air bag inflates, the nitrogen gas is at a pressure of 1.30 atmospheres, a temperature of 301 K, and has a volume of 40.0 liters. In the space in your answer booklet, calculate the volume of the nitrogen gas at STP. Your response must include both a correct numerical setup and the calculated volume. [2]
51. What is the total number of moles in 80.0 grams of C2H5Cl (gram-formula mass = 64.5 grams/mole)? [1]
52. In the space in your answer booklet, show a correct numerical setup for calculating the
formula mass of glucose, C6H12O6. [1]
53. Write the empirical formula for the compound C6H12O6. [1]
Base your answers to questions 54 through 56 on the information below.
Naphthalene, a nonpolar substance that sublimes at room temperature, can be used to protect wool clothing from being eaten by moths.
54. Explain, in terms of intermolecular forces, why naphthalene sublimes. [1]
55. Explain why naphthalene is not expected to dissolve in water. [1]
56. The empirical formula for naphthalene is C5H4 and the molecular mass of naphthalene is 128 grams/mole. What is the molecular formula for naphthalene? [1]
Base your answers to questions 57 through 59 on the information below.
The decomposition of sodium azide, NaN3(s), is used to inflate airbags. On impact, the
NaN3(s) is ignited by an electrical spark, producing N2(g) and Na(s). The N2(g) inflates the airbag.
57. Balance the equation in your answer booklet, using the smallest whole-number coefficients. [1]
58. What is the total number of moles present in a 52.0-gram sample of NaN3(s) (gram-formula mass = 65.0 gram/mole)? [1]
59. An inflated airbag has a volume of 5.00 . 104 cm3 at STP. The density of N2(g) at STP is 0.00125 g/cm3. What is the total number of grams of N2(g) in the airbag? [1]
60. Given the balanced equation:
4Al(s) + 3O2(g) → 2Al2O3(s)
What is the total number of moles of O2(g) that must react completely with 8.0 moles of Al(s) in order to form Al2O3(s)? [1]
61. Given the equation: 2 H2(g) + O2(g) → 2 H2O(g)
If 8.0 moles of O2 are completely consumed, what is the total number of moles of H2O produced? [1]
62. What is the gram-formula mass of (NH4)2CO3? Use atomic masses rounded to the nearest whole number. [1]
63. In the space provided in your answer booklet, show a correct numerical setup for calculating the number of moles of CO2 (gram-formula mass = 44 g/mol) present in 11 grams of CO2. [1]
64. Balance the equation in your answer booklet, using the smallest whole-number coefficients. [1]
______C5H12(g) + ______O2(g) → ______CO2(g) + ______H2O(g)
65. a Using your balanced equation, show a correct numerical setup for calculating the total number of moles of H2O(g) produced when 5.0 moles of O2(g) are completely consumed. Use the space provided in your answer booklet. [1]
b Record your answer. [1]
66. In a laboratory experiment, a student determined the mass of the product, NaCl(s), to be 1.84 grams.
a Calculate the gram formula mass of NaCl(s). Round atomic masses from the Periodic Table to the nearest tenth. Show all work. [1]
Indicate the correct answer, including an appropriate unit. [1]
b Calculate the number of moles of NaCl(s) produced. Show all work. [1]
Indicate the correct answer. [1]
67. What is the mass of 4.76 moles of Na3PO4 (gram-formula mass = 164 grams/mole)? [1]