Deck 3: Stoichiometry

Question 1

How many moles of P₄ molecules molecules are in 145.2 g of phosphorus?

A) 1.172 mol
B) 1.452 × 10¹ mol
C) 4.688 mol
D) 2.411 × 10¹ mol
E) 1.799 × 10⁴ mol

Answer 1

1.172 mol

Question 2

A sample of iron weighing 15.0 g contains how many moles of iron atoms?

A) 3.72 mol
B) 0.269 mol
C) 0.118 mol
D) 0.577 mol
E) 0.0780 mol

Answer 2

0.269 mol

Question 3

Bromine exists naturally as a mixture of bromine-79 and bromine-81 isotopes. An atom of bromine-79 contains

A) 79 protons, 79 electrons, and 35 neutrons.
B) 35 protons, 44 neutrons, and 35 electrons.
C) 44 protons, 44 electrons, and 35 neutrons.
D) 34 protons and 35 electrons only.
E) 35 protons, 79 neutrons, and 35 electrons.

Answer 3

35 protons, 44 neutrons, and 35 electrons.

Question 4

Boron naturally occurs in two isotopic forms. The more common isotope is ¹¹B (atomic mass 11.01 amu), which is 80.00% abundant. The average atomic mass of boron is 10.81. What is the mass of the other isotope?

A) 10.91 amu.
B) 10.01 amu.
C) 10.81 amu.
D) 11.00 amu.
E) 11.01 amu.

Question 5

Consider the new element moonium, atomic number 118, atomic mass 273.2 g. The nucleus of an atom of moonium-273 contains

A) 118 protons, 118 alpha particles.
B) 118 protons, 155 neutrons.
C) 118 protons, 273neutrons.
D) 118protons, 155 neutrons, 118 electrons.
E) 118protons, 118neutrons.

Question 6

What is the molar mass of ethanol (C₂H₅OH)?

A) 46.07
B) 62.07
C) 45.07
D) 38.90
E) 34.17

Question 7

Indium has atomic number 49 and atomic mass 114.8 g. Naturally occurring indium contains a mixture of indium-112 and indium-115 in an atomic ratio of approximately

A) 75/25.
B) 25/75.
C) 6/94.
D) 50/50.
E) 94/6.

Question 8

How many molecules of ammonia are present in 6.9 g of ammonia?

A) 6.7 × 10^-25
B) 4.1 × 10¹
C) 8.3 × 10²³
D) 4.2 × 10²⁴
E) 2.4 × 10²³

Question 9

How many atoms of hydrogen are present in 4.0 g of ammonia?

A) 7.8 × 10²⁴
B) 0.70
C) 4.2 × 10²³
D) 1.2 × 10^-24
E) 1.8 × 10²⁴

Question 10

What is the mass (in grams) of one molecule of phosphorus pentachloride?

A) 1.25 × 10²⁶ g
B) 3.46 × 10^-22 g
C) 1.10 × 10^-22 g
D) 208.22 g
E) 1.00 g

Question 11

For which of the following compounds does 1.0 g represent 2.27 × 10^-2 mol?

A) ​H₂O
B) ​C₂H₆
C) NH₃
D) ​CO₂
E) ​CO

Question 12

For which compound does 0.256 mole weigh 12.9 g?

A) C₂H₄O₂
B) C₂H₆
C) CH₃Cl
D) CO₂
E) C₂H₄O

Question 13

Calculate the molar mass of a sample if a single molecule weighs 5.34 × 10^-23g.

A) 12.0 g/mol
B) 5.34 × 10^-23 g/mol
C) 1.13 × 10⁴⁶ g/mol
D) 32.2 g/mol
E) none of these

Question 14

Iron is biologically important in the transport of oxygen by red blood cells from the lungs to the various organs of the body. In the blood of an adult human, there are approximately 2.60 × 10¹³ red blood cells with a total of 2.90 g of iron. On the average, how many iron atoms are present in each red blood cell? (molar mass for Fe = 55.85 g)

A) 8.33 × 10^-10
B) 1.20 × 10⁹
C) 5.19 × 10^-2
D) 3.12 × 10²²
E) 2.60 × 10¹³

Question 15

A single atom of an element weighs 5.81 × 10^-23 g. Identify the isotope.

A) (³⁵Cl)
B) (¹⁰³Rh)
C) (⁸⁰Br)
D) (⁴⁵Sc)
E) none of these

Question 16

For a new element, 60.54% is an isotope with mass 282.1 amu, 3.28% is an isotope with mass 283.2 amu, and 36.18% is an isotope with mass 284.6 amu. Calculate the average atomic mass of this new element.

A) 283.3 amu
B) 849.9 amu
C) 282.1 amu
D) 283.0 amu
E) 314.5 amu

Question 17

The average mass of a boron atom is 10.81. If you were able to isolate a single boron atom, what is the chance that you would randomly get an atom with mass 10.81?

A) greater than 50%
B) 0%
C) 0.81%
D) 10.81%
E) about 11%

Question 18

The atomic mass of rhenium is 186.2. Given that 37.1% of natural rhenium is rhenium-185, what is the other stable isotope?

A)
B)
C)
D)
E)

Question 19

An alkali metal oxide contains 83.01% metal by mass. Determine the identity of the metal.

A) Cs
B) Li
C) K
D) Na
E) Rb

Question 20

Which compound has the smallest molar mass?

A) C₂H₆
B) CH₃Cl
C) CO₂
D) C₂H₄O
E) none of these

Question 21

You find a compound composed only of element X and hydrogen, and you know that it is 91.33% element X by mass. Each molecule has 2.67 times as many H atoms as X atoms. What is element X?

A) Cu
B) Si
C) Cl
D) C
E) Ne

Question 22

The molar mass of the insecticide dibromoethane is 187.9 g/mol. Its molecular formula is C₂H₄Br₂. How many atoms of carbon are in a sample of dibromoethane weighing 1.879 g?

A) none of these
B) 1.204 × 10²²
C) 6.022 × 10^0.21
D) 6.022 × 10²¹
E) 12.04 × 10⁴⁴

Question 23

What is the percent by mass of hydrogen in ammonium acetate?

A) 7.07%
B) 5.23%
C) 14.3%
D) 3.92%
E) 9.15%

Question 24

Phosphorus has the molecular formula P₄ and sulfur has the molecular formula S₈. How many grams of phosphorus contain the same number of molecules as 6.41 g of sulfur?

A) 6.19 g
B) 6.41 g
C) 3.21 g
D) 3.10 g
E) none of these

Question 25

The mass of 0.82 mol of a diatomic molecule is 131.3g. Identify the molecule.

A) Xe
B) Cl₂
C) I₂
D) F₂
E) Br₂

Question 26

The empirical formula of sugar is CH₂O and its molar mass is 180.2 g/mole. If one teaspoon of sugar weighs 3.50 g, how many moles of sugar and how many molecules of sugar are present?

A) 0.0194 mole, 3.24 × 10²⁶ molecules
B) 0.0295 mole, 1.78 × 10²² molecules
C) 0.0583 mole, 3.51 × 10²² molecules
D) 0.0194 mole, 1.17 × 10²² molecules
E) 0.117 mole, 7.03 × 10²² molecules

Question 27

A given sample of xenon fluoride contains molecules of a single type, XeF_n, where n is some whole number. Given that 9.03 × 10²⁰ molecules of XeF_n weigh 0.311 g, calculate n.

A) 2
B) 4
C) 1
D) none of these

Question 28

What mass of styrene (molar mass 104.1 g/mol) contains 4.50 × 10²⁰ molecules of styrene?

A) 7.78 × 10^-2 g
B) 7.48 × 10⁴ g
C) 0.00778 g
D) 7.48 × 10^-4 g
E) 7.48 × 10^-3 g

Question 29

Cortisone consists of molecules, each of which contains 21 atoms of carbon (plus other atoms). The mass percentage of carbon in cortisone is 69.98%. What is the molar mass of cortisone?

A) 287.6 g/mol
B) 360.4 g/mol
C) 176.5 g/mol
D) 252.2 g/mol
E) 312.8 g/mol

Question 30

Roundup, an herbicide manufactured by Monsanto, has the formula C₃H₈NO₅P. How many moles of molecules are there in a 500.-g sample of Roundup?

A) 84.5
B) 2.96
C) 0.338
D) 1.75
E) none of these

Question 31

Compound X₂Y is 60% X by mass. Calculate the percent Y by mass of the compound X₂Y₂.

A) 30%
B) 80%
C) 40%
D) 20%
E) 60%

Question 32

The molar mass of the insecticide dibromoethane is 187.9. Its molecular formula is C₂H₄Br₂. What percent by mass of bromine does dibromoethane contain?

A) 50.0%
B) 37.8%
C) 42.5%
D) 89.3%
E) 85.0%

Question 33

Which of the following contains the greatest percentage of nitrogen by mass?

A) NH₃
B) HCN
C) C₆H₄N₃O₆
D) N₂O
E) NO₂

Question 34

A substance contains 3.024 g hydrogen, 30.97 g phosphorus, and 64.00 g oxygen. How many grams of oxygen are in an 85.00-g sample of the substance?

A) 64.00 g
B) 130.1 g
C) 16.00 g
D) 55.51 g
E) none of these

Question 35

NaHCO₃ is the active ingredient in baking soda. How many grams of oxygen are in 0.36 g of NaHCO₃?

A) 0.0043 g
B) 0.21 g
C) 0.013g
D) 0.069 g
E) 1.1 g

Question 36

An oxybromate compound, NaBrO_x, where x is a whole number, is analyzed and found to contain 52.95% Br by mass. What is x?

A) 0
B) 1
C) 2
D) 3
E) 4

Question 37

A hydrate of copper(II) sulfate is 25.5% copper by mass. How many water molecules are there for each unit of copper(II) sulfate?

A) 1
B) 2
C) 3
D) 4
E) 5

Question 38

Find the percent sulfur (atoms) by mass in sodium sulfide.

A) 52.1%
B) 58.2%
C) 41.1%
D) 74.4%
E) 73.6%

Question 39

Which of the following compounds has the same percent composition by mass as styrene, C₈H₈?

A) cyclobutadiene, C₄H₄
B) α-ethyl naphthalene, C₁₂H₁₂
C) acetylene, C₂H₂
D) benzene, C₆H₆
E) all of these

Question 40

A mixture of NaCl and NaNO₃ is 31.7% sodium by mass. What is the approximate percent of NaCl in this mixture?

A) 32%
B) 30%
C) 38%
D) 36%
E) 34%

Question 41

When the following equation is balanced, what is the sum of the coefficients?
Al₂(SO₄)₃ + Ca(OH)₂ → Al(OH)₃ + CaSO₄

A) 10
B) 8
C) 4
D) 9
E) 3

Question 42

Caffeine consists of carbon, hydrogen, oxygen, and nitrogen. When 0.1920 g of caffeine is burned in an excess of oxygen, 0.3482 g of carbon dioxide and 0.0891 g water are formed. Caffeine is 28.84% nitrogen by mass. Its molar mass is between 190 and 200 g/mol. What is the formula for caffeine?

A) C₆H₄N₄O₄
B) C₈H₁₀N₄O₂
C) C₄H₅N₂O
D) C₃H₂N₂O₂
E) none of these

Question 43

What is the subscript of aluminum in the formula of aluminum phosphate?

A) 3
B) 1
C) 2
D) 0
E) 4

Question 44

wPCl₅ + xH₂O → yPOCl₃ + zHCl
When the equation is properly balanced, what are the coefficients?

A) w = 1, x = 1, y = 1, z = 2
B) w = 2, x = 2, y = 2, z = 2
C) w = 1, x = 2, y = 2, z = 4
D) w = 2, x = 2, y = 2, z = 4
E) none of these

Question 45

Adipic acid contains 49.32% C, 43.84% O, and 6.85% H by mass. What is the empirical formula?

A) C₂H₅O₄
B) C₃H₅O₂
C) C₂HO₃
D) C₃H₃O₄
E) C₃HO₃

Question 46

The mass percent of iron in an iron oxide is 77.7%. Find the empirical formula.

A) Fe₃O₂
B) Fe₃O₄
C) Fe₂O₃
D) FeO
E) none of these

Question 47

TNT consists of carbon, nitrogen, oxygen, and hydrogen. It is 37.02% carbon by mass, 18.49% nitrogen by mass, and 42.27% oxygen by mass. The molar mass of TNT is between 210 g/mol and 245 g/mol. What is the molecular formula for TNT?

A) C₄H₇N₆O₆
B) C₆H₄N₃O₆
C) C₇H₅N₃O₆
D) C₈H₁₂N₃O₄
E) none of these

Question 48

Which of the following equations correctly describes the combustion of CH₄ and O₂ to produce water (H₂O) and carbon dioxide (CO₂)?

A) CH₄ + (1/2)O₂ → CO₂ + H₂O
B) CH₄ + 2O₂ → CO₂ + 2H₂O
C) CH₄ + 3O₂ → 2CO₂ + H₂O
D) CH₄ + O₂ → CO₂ + 2H₂O

Question 49

Vitamin C contains the elements C, H, and O. It is known to contain 40.9% C and 4.58% H by mass. The molar mass of vitamin C has been found to be about 180. The molecular formula for vitamin C is

A) C₆H₈O₆
B) C₄H₆O₄
C) C₃H₄O₃
D) C₂H₃O₂
E) none of these

Question 50

When the equation FeCr₂O₄ + K₂CO₃ + O₂ → K₂CrO₄ + Fe₂O₃ + CO₂ is balanced with the smallest set of integers, the sum of the coefficients is

A) 9
B) 15
C) 6
D) 37
E) 24

Question 51

When the equation C₆H₁₄ + O₂ → CO₂ + H₂O is balanced with the smallest set of integers, the sum of the coefficients is

A) 28
B) 33
C) 47
D) 4
E) 40

Question 52

What is the empirical formula of a hydrocarbon (a compound that consists of only carbon and hydrogen) that contains 81.7% carbon by mass?

A) C₅H₁₂
B) C₃H₈
C) C₄H₁₀
D) C₂H₆
E) none of these

Question 53

A 0.4647-g sample of a compound known to contain only carbon, hydrogen, and oxygen was burned in oxygen to yield 0.8635 g of CO₂ and 0.1767 g of H₂O. What is the empirical formula of the compound?

A) C₃H₃O₂
B) C₂H₂O
C) C₆H₃O₂
D) C₃H₆O₂
E) CHO

Question 54

Consider the following unbalanced equation:
C₄H₁₀ + O₂ → CO₂ + H₂O
For every 1.0 mol of C₄H₁₀, ___ mol of O₂ is required.

A) 1.0
B) 8.0
C) 13.0
D) 6.5
E) none of these

Question 55

The empirical formula of a group of compounds is CHCl. Lindane, a powerful insecticide, is a member of this group. The molar mass of lindane is 290.8. How many atoms of carbon does a molecule of lindane contain?

A) 6
B) 4
C) 3
D) 8
E) 2

Question 56

The empirical formula of styrene is CH; its molar mass is 104.1. What is the molecular formula of styrene?

A) C₂H₄
B) C₈H₈
C) C₆H₆
D) C₁₀H₁₂
E) none of these

Question 57

In the balanced equation for the reaction
[A]P₄O₆(s) + [B]H₂O(l) → [C]H₃PO₃(aq)
If [A] equals 2, the coefficient [C] equals

A) 6
B) 4
C) 2
D) 10
E) none of these

Question 58

Give (in order) the correct coefficients to balance the following reaction:
H₂SnCl₆ + H₂S → SnS₂ + HCl

A) 1, 2, 2, 2
B) 1, 2, 1, 6
C) 1, 1, 1, 6
D) 6, 2, 1, 1
E) 2, 4, 2, 6

Question 59

Potassium forms an oxide containing 1 oxygen atom for every 2 atoms of potassium. What is the coefficient of oxygen in the balanced equation for the reaction of potassium with oxygen to form this oxide?

A) 0
B) 1
C) 2
D) 3
E) 4

Question 60

A 2.00-g sample of an oxide of bromine is converted to 2.936 g of AgBr. Calculate the empirical formula of the oxide. (molar mass for AgBr = 187.78)

A) BrO₃
B) BrO
C) BrO₂
D) Br₂O
E) none of these

Question 61

A reaction occurs between sodium carbonate and hydrochloric acid producing sodium chloride, carbon dioxide, and water. The correct set of coefficients, respectively, for the balanced reaction is

A) 5, 10, 10, 5, 5.
B) 1, 2, 2, 1, 1.
C) 8, 6, 5, 10, 5.
D) 3, 6, 6, 3, 4.
E) none of these

Question 62

Indium reacts with chlorine to form InCl₃. In the balanced equation for this reaction, the coefficient of the indium trichloride is

A) 6
B) 4
C) 2
D) 3
E) 1

Question 63

When rubidium metal is exposed to air, one atom of rubidium, Rb, combines with two atoms of oxygen. If 1.75 g of rubidium is exposed to air, what will be the mass of the product in grams?

A) 0.655 g
B) 1.37 g
C) 0.328 g
D) 2.41 g
E) 2.08 g

Question 64

29.4 g of Al and 25.0g of Br₂ react according to the following equation:
2Al + 3Br₂ → 2AlBr₃
What mass of AlBr₃ is formed, assuming 100% yield?

A) 62.6 g
B) 291 g
C) 27.8 g
D) 54.4 g
E) 41.7 g

Question 65

Baking powder, a mixture of cream of tartar (KHC₄H₄O₆, molar mass 188 g/mol) and baking soda (NaHCO₃, molar mass 84.0 g/mol), undergoes the following reaction at baking temperatures:
KHC₄H₄O₆ + NaHCO₃ → KNaC₄H₄O₆ + H₂O + CO₂
(The CO₂ makes the cake rise.) A recipe calls for two level teaspoons (a total of 8.0 g) of cream of tartar. How much baking soda must be added for both materials to react completely?

A) 8.0 g
B) 0.45 g
C) 3.6 g
D) 18 g
E) none of these

Question 66

How many grams of Ca(NO₃)₂ can be produced by reacting excess HNO₃ with 7.40 g of Ca(OH)₂?

A) 10.2 g
B) 16.4 g
C) 7.40 g
D) 8.22 g
E) 32.8 g

Question 67

The limiting reactant in a reaction

A) is the reactant for which you have the least number of moles.
B) has the lowest coefficient in a balanced equation.
C) has the lowest ratio of coefficient in the balanced equation to moles available.
D) has the lowest ratio of moles available to coefficient in the balanced equation.
E) none of these

Question 68

Iron is produced from its ore by the following reactions:
2C(s) + O₂(g) → 2CO(g)
Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)
How many moles of C_(s) are needed to produce 2.4 mol Fe(s)?

A) 3.6 mol C
B) 2.4 mol C
C) 5.0 mol ​C
D) 1.6 mol C

Question 69

One commercial system removes SO₂ emissions from smoke at 95.0°C by the following set of balanced reactions:
SO₂(g) + Cl₂ → SO₂Cl₂(g)
SO₂Cl₂ + 2H₂O → H₂SO₄ + 2HCl
H₂SO₄ + Ca(OH)₂ → CaSO₄(s) + 2H₂O
Assuming the process is 95.0% efficient, how many grams of CaSO₄ may be produced from 1.00 × 10² g of SO₂ (molar masses: SO₂, 64.1 g/mol; CaSO₄, 136 g/mol)?

A) 47.1 g
B) 212 g
C) 202 g
D) 87.2 g
E) 44.8 g

Question 70

Sulfuric acid may be produced by the following process:



How many moles of H₂SO₄ will be produced form 5.00 mol of FeS₂?

A) 12.2 mol
B) 20.0 mol
C) 6.11 mol
D) 10.0 mol
E) 5.00 mol

Question 71

When the equation NH₃ + O₂ → NO + H₂O is balanced with the smallest set of integers, the sum of the coefficients is

A) 4
B) 24
C) 12
D) 14
E) 19

Question 72

Consider the following two reactions. ​How much water (in grams) is produced from 10.0 g of Mg?

A) 3.71 g
B) 18.0 g
C) 7.41 g
D) 1.85 g
E) none of these

Question 73

How many grams of H₂O will be formed when 39.0 g H₂ is mixed with 49.6 g O₂ and allowed to completely react to form water?

A) 88.6 g
B) 55.8 g
C) 27.9 g
D) 351 g
E) 59.1 g

Question 74

The refining of aluminum from bauxite ore (which contains 50.% Al₂O₃ by mass) proceeds by the overall reaction 2Al₂O₃ + 3C → 4Al + 3CO₂. How much bauxite ore is required to give the 5.0 × 10¹³ g of aluminum produced each year in the United States? (Assume 100% conversion.)

A) 1.9 × 10¹⁴ g
B) 7.6 × 10¹⁴ g
C) 1.3 × 10¹³ g
D) 5.3 × 10¹³ g

Question 75

In the reaction
2A + 3B → C
4)0 mol A react with 4.0 mol B. Which reactant is limiting?

A) A is limiting because there are 2 mol of it but 4.0 mol are needed.
B) B is limiting because there are 4.0 mol of it but 6.0 mol are needed.
C) A is limiting because 2 is smaller than 3 (the coefficients in the balanced equation).
D) Neither is limiting because equal amounts (4.0 mol) of each reactant are used.
E) B is limiting because 3 is larger than 2 (the coefficients in the balanced equation).

Question 76

A 6.32-g sample of potassium chlorate was decomposed according to the following equation:
2KClO₃ → 2KCl + 3O₂
How many moles of oxygen are formed?

A) 0.051 mol
B) 0.0774 mol
C) 0.0344 mol
D) 1.65 mol
E) none of these

Question 77

A 7.66-g sample of AgNO₃ is reacted with BaCl₂ according to the equation
2AgNO₃(aq) + BaCl₂(aq) → 2AgCl(s) + Ba(NO₃)₂(aq)
To give 4.34 g of AgCl. What is the percent yield of AgCl?

A) 47.8%
B) 56.7%
C) 67.2%
D) 33.6%
E) 20.1%

Question 78

Consider the following reaction:
CH₄(g) + 4Cl₂(g) → CCl₄(g) + 4HCl(g)
What mass of CCl₄ is formed by the reaction of 8.00 g of methane with an excess of chlorine?

A) 14.2 g
B) 7.10 g
C) 76.7 g
D) 1.42 g
E) none of these

Question 79

How many moles of sodium phosphate are required to react completely with 3.0 mol of calcium nitrate to form sodium nitrate and calcium phosphate?

A) 2.0 mol
B) 3.0 mol
C) 1.0 mol
D) 1.5 mol
E) 4.5 mol

Question 80

Consider the following unbalanced equation:
KO₂ + H₂O → KOH + O₂ + H₂O₂
For every 3.0 mol of KO₂, ___ mol of H₂O is needed for a complete reaction.

A) 6.0
B) 2.0
C) 3.0
D) 1.0
E) none of these