Deck 3: Stoichiometry

Question 1

What is the molar mass of ethanol (C₂H₅OH)?

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

Answer 1

46.07

Question 2

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 2

35 protons, 44 neutrons, and 35 electrons.

Question 3

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

Answer 3

CO₂

Question 4

An alkali metal oxide contains 46.45% metal by mass. Determine the identity of the metal.

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

Question 5

For which compound does 0.256 mole weigh 12.9 g?

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

Question 6

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 7

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 8

A sample of iron weighing 18.4 g contains how many moles of iron atoms?

A) 3.04 mol
B) 0.329 mol
C) 0.145 mol
D) 0.708 mol
E) 0.0957 mol

Question 9

Consider the new element moonium, atomic number 114, atomic mass 273.2 g. The nucleus of an atom of moonium-273 contains

A) 114 protons, 114 alpha particles.
B) 114 protons, 159 neutrons.
C) 114 protons, 273 neutrons.
D) 114 protons, 159 neutrons, 114 electrons.
E) 114 protons, 114 neutrons.

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

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 12

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 13

How many moles of P₄ molecules molecules are in 141.4 g of phosphorus?

A) 1.141 mol
B) 1.414 * 10¹ mol
C) 4.566 mol
D) 2.348 * 10¹ mol
E) 1.752 *10⁴ mol

Question 14

How many molecules of ammonia are present in 7.5 g of ammonia?

A) 7.3*10^-25
B) 4.4*10¹
C) 9.0 *10²³
D) 4.5* 10²⁴
E) 2.7 *10²³

Question 15

Which compound has the smallest molar mass?

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

Question 16

For a new element, 60.78% is an isotope with mass 281.9 amu, 2.32% is an isotope with mass 283.7 amu, and 36.90% is an isotope with mass 284.5 amu. Calculate the average atomic mass of this new element.

A) 283.4 amu
B) 850.1 amu
C) 281.9 amu
D) 282.9 amu
E) 314.3 amu

Question 17

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

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 18

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 19

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 20

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 21

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

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

Question 22

Find the percent oxygen (atoms) by mass in potassium oxide.

A) 27.4%
B) 29.0%
C) 17%
D) 45.7%
E) 45.0%

Question 23

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 24

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 25

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 26

NaHCO₃ is the active ingredient in baking soda. How many grams of oxygen are in 0.31 g of NaHCO₃?

A) 0.0037 g
B) 0.18 g
C) 0.011 g
D) 0.059 g
E) 0.9 g

Question 27

An oxybromate compound, KBrO_x, where x is a whole number, is analyzed and found to contain 47.84% Br by mass. What is x?

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

Question 28

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

A) Xe
B) Cl₂
C) I₂
D) F₂
E) Br₂

Question 29

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 30

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

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

Question 31

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 32

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 33

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 34

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 35

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 36

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 37

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 38

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 39

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 40

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 41

Consider the following unbalanced equation: C₄H₁₀ + O₂ $\rightarrow$ 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 42

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 43

When the equation C₄H₁₀ + O₂ $\rightarrow$ CO₂ + H₂O is balanced with the smallest set of integers, the sum of the coefficients is

A) 20
B) 23
C) 33
D) 4
E) 28

Question 44

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 45

Give (in order) the correct coefficients to balance the following reaction: H₂SnCl₆ + H₂S $\rightarrow$ 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 46

wPCl₅ + xH₂O $\rightarrow$ 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 47

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

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

Question 48

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 49

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 50

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 51

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

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

Question 52

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 $\rightarrow$ CO₂ + H₂O
B) CH₄ + 2O₂ $\rightarrow$ CO₂ + 2H₂O
C) CH₄ + 3O₂ $\rightarrow$ 2CO₂ + H₂O
D) CH₄ + O₂ $\rightarrow$ CO₂ + 2H₂O

Question 53

When the equation FeCr₂O₄ + K₂CO₃ + O₂ $\rightarrow$ 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 54

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 55

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 56

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

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

Question 57

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 58

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 59

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 60

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 61

In the reaction 2A + 3B $\rightarrow$ 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 62

A 6.32-g sample of potassium chlorate was decomposed according to the following equation: 2KClO₃ $\rightarrow$ 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 63

How many grams of H₂O will be formed when 42.0 g H₂ is mixed with 38.0 g O₂ and allowed to completely react to form water?

A) 80.0 g
B) 42.8 g
C) 21.4 g
D) 378 g
E) 53.3 g

Question 64

When the equation NH₃ + O₂ $\rightarrow$ 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 65

A 8.84-g sample of AgNO₃ is reacted with BaCl₂ according to the equation 2AgNO₃(aq) + BaCl₂(aq) $\rightarrow$ 2AgCl(s) + Ba(NO₃)₂(aq)
To give 5.58 g of AgCl. What is the percent yield of AgCl?

A) 53.3%
B) 63.1%
C) 74.8%
D) 37.4%
E) 22.4%

Question 66

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 67

Consider the following reaction: CH₄(g) + 4Cl₂(g) $\rightarrow$ 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 68

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 69

Iron is produced from its ore by the following reactions: 2C(s) + O₂(g) $\rightarrow$ 2CO(g)
Fe₂O₃(s) + 3CO(g) $\rightarrow$ 2Fe(s) + 3CO₂(g)
How many moles of O₂(g) are needed to produce 1.4 mol Fe(s)?

A) 1.1 mol O₂
B) 0.7 mol O₂
C) 4.0 mol O₂
D) 2.1 mol O₂

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 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 72

How many moles of sodium phosphate are required to react completely with 5.4 mol of calcium nitrate to form sodium nitrate and calcium phosphate?

A) 3.6 mol
B) 5.4 mol
C) 1.8 mol
D) 2.7 mol
E) 8.1 mol

Question 73

The refining of aluminum from bauxite ore (which contains 50.% Al₂O₃ by mass) proceeds by the overall reaction 2Al₂O₃ + 3C $\rightarrow$ 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 74

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 75

One commercial system removes SO₂ emissions from smoke at 95.0°C by the following set of balanced reactions: SO₂(g) + Cl₂ $\rightarrow$ SO₂Cl₂(g)
SO₂Cl₂ + 2H₂O $\rightarrow$ H₂SO₄ + 2HCl
H₂SO₄ + Ca(OH)₂ $\rightarrow$ 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 76

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 77

21.4 g of Al and 14.6 g of Br₂ react according to the following equation: 2Al + 3Br₂ $\rightarrow$ 2AlBr₃
What mass of AlBr₃ is formed, assuming 100% yield?

A) 36.5 g
B) 212 g
C)16.2 g
D) 36.0 g
E) 24.4 g

Question 78

Consider the following unbalanced equation: KO₂ + H₂O $\rightarrow$ 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

Question 79

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 80

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 $\rightarrow$ 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