Deck 3: Stoichiometry: Mass, Formulas, and Reactions

Question 1

A sample of water (H₂O) contains 1.81 * 10²⁴ molecules. How many moles of atoms are there in this sample?

A) 1.00
B) 2.00
C) 3.00
D) 6.00
E) 9.00

Answer 1

9.00

Question 2

In one analysis, the density of ozone in an air sample was found to be 5.00 *10^-8 mol/L. What is the density in molecules per liter?

A) 8.30 *10^-32
B) 3.01 * 10¹⁶
C) 1.81 *10^-11
D) 3.01 *10¹¹
E) 6.02 * 10²³

Answer 2

3.01 * 10¹⁶

Question 3

A tiny speck (8.3*10^-7 mol) of radioactive americium-241 is used in smoke detectors. How many atoms of americium-241 are there in one of these smoke detectors?

A) 5.0 * 10¹⁷
B) 1.2 * 10²⁰
C) 2.9 * 10²²
D) 6.0 * 10²³
E) 8.3 * 10⁷

Answer 3

5.0 * 10¹⁷

Question 4

A gallon of water has a mass of 3.79 kg. How many moles of water (18.02 g/mol) is this?

A) 0.210 mol
B) 210 mol
C) 68.3 mol
D) 68,300 mol
E) 386 mol

Question 5

A quart of water has a mass of 0.948 kg. How many moles of water (18.02 g/mol) is this?

A) 0.0526 mol
B) 52.6 mol
C) 17.1 mol
D) 17,100 mol
E) 171 mol

Question 6

Which statement A-D regarding the terms mole and molar mass is not correct?

A) A mole is defined as the number of particles in exactly 12 g of carbon-12.
B) A mole of oxygen gas contains 6.022 * 10²³ molecules.
C) Two moles of oxygen atoms can be obtained by decomposing one mole of carbon dioxide.
D) To obtain the molar mass in grams (g/mol) from the atomic mass in atomic mass units (u), multiply by 6.022 * 10²³/mol and divide by 6.022*10²³ u/g.
E) Statements A-D all are correct.

Question 7

Which statement about the following chemical reaction is not correct?
3H₂ + N₂ $\rightarrow$ 2NH₃

A) For every nitrogen molecule consumed, two molecules of ammonia are produced.
B) For every two molecules of nitrogen consumed, three molecules of ammonia are produced.
C) For every three molecules of hydrogen consumed, two molecules of ammonia are produced.
D) For every two molecules of ammonia produced, three molecules of hydrogen are consumed.
E) One molecule of nitrogen reacts with three molecules of hydrogen.

Question 8

Which of the following contains the largest number of atoms?

A) 1 mol water
B) 1 mol phosphorus trichloride
C) 1 mol dinitrogen pentoxide
D) 1 mol carbon dioxide
E) All of these contain the same number of atoms.

Question 9

In one analysis, 3.01 *10¹³ molecules of ozone were found in 1.00 mL of an air sample. How many moles of ozone is this?

A) 5.00 * 10^-11 mol
B) 1.81 * 10³⁷ mol
C) 1.81 *10^-11 mol
D) 5.00 * 10³⁷ mol
E) 6.02 *10^-23 mol

Question 10

Which substance listed below contains the most oxygen atoms?

A) 1 mol of Al₂O₃
B) 1 mol of Fe₂O₃
C) 2 mol of N₂O₄
D) 2 mol of CO₂
E) 2 mol of HNO₃

Question 11

Which statement about the following chemical reaction is not correct?
2H₂ + O₂ $\rightarrow$ 2H₂O

A) For every oxygen molecule consumed, two water molecules are produced.
B) For every two hydrogen molecules consumed, two water molecules are produced.
C) Two hydrogen molecules react with one oxygen molecule.
D) Four hydrogen molecules react with oxygen to produce two water molecules.
E) Four hydrogen atoms combine with two oxygen atoms to produce two water molecules.

Question 12

The mass of 0.25 mol of some element is 8.0 g. What is the element?

A) O₂
B) N₂
C) Cl₂
D) Br₂
E) H₂

Question 13

How many atoms of chlorine are there in 25.0 g of calcium chloride (CaCl₂)?

A) 1.36 * 10²³ atoms
B) 2.67 * 10²⁴ atoms
C) 2.71 *10²³ atoms
D) 1.95 * 10²³ atoms

Question 14

Which one of the following samples contains the fewest number of molecules? H is used as the symbol for hydrogen-1, and D is used as the symbol for hydrogen-2.

A) 42 g of D₂O
B) 2 moles of H₂O
C) 2 moles of D₂O
D) 36 g of H₂O
E) 39 g of D₂O

Question 15

Identify the correct statement regarding the mole.

A) A mole of oxygen gas contains 6.02 *10²³ atoms.
B) A mole of chlorine gas contains 2 *6.02 * 10²³ molecules.
C) A mole of carbon dioxide contains two moles of oxygen atoms.
D) A mole of ammonia gas (NH₃) has a mass of 34.0 g.
E) A mole consists of the number of particles in exactly 12 g of naturally occurring carbon.

Question 16

A particular manufacturer sells phosphoric acid capsules as a homeopathic remedy with a concentration specified as 23X. (23X means that when averaged over many capsules, the average mass of phosphoric acid in one capsule is 10^-23 times the mass of the capsule. The rest is a carbohydrate filler.) If each capsule has a mass of 35 mg, approximately how many capsules would you have to take to expect to ingest at least one molecule of H₃PO₄ (98.0 g/mol)?

A) 1
B) 5
C) 50
D) 500
E) 5000

Question 17

How many gold atoms are there in a 1.00 kg bar of gold?

A) 3.06 *10²⁴
B) 197 mol
C) 3.06 *10²¹
D) 5.08 *10^-3 mol
E) 5.08 * 10¹⁸

Question 18

One mole is defined as __________

A) the number of particles equal to the number of atoms in exactly 12 g of carbon-12.
B) the number of particles equal to the number of atoms in exactly 16 g of oxygen-16.
C) exactly 6.02 *10²² particles.
D) the number of particles equal to the number of atoms in exactly 1 g of hydrogen-1.
E) the number of particles equal to the number of atoms in exactly 1 kg of carbon in a vault at the National Bureau of Standards.

Question 19

How many moles of ammonia are there in a 346 g sample of pure NH₃ (17.03 g/mol)?

A) 0.0496 mol
B) 20.3 mol
C) 24.7 mol
D) 5,930 mol
E) 3.46 mol

Question 20

A tiny speck (2.0 * 10^-4 g) of radioactive americium-241 (241.06 g/mol) is used in smoke detectors. How many atoms of americium-241 are there in one of these smoke detectors?

A) 5.0 * 10¹⁷ atoms
B) 1.2 * 10²⁰ atoms
C) 2.9 * 10²² atoms
D) 6.0 * 10²³ atoms
E) 8.3 * 10⁷ atoms

Question 21

Platinum (195.078 g/mol) once sold for $560/oz. One ounce is equal to 28.35 g. How many platinum atoms could you buy with a penny ($0.01)?

A) 5.0*10²⁰ atoms
B) 2.6 * 10⁶ atoms
C) 6.5 *10¹⁹ atoms
D) 1.6 *10¹⁸ atoms
E) 5.1*10¹⁸ atoms

Question 22

Hydrogen peroxide decomposes to produce water and oxygen. Which relationship regarding the quantities of reactants and products associated with this reaction is not correct?
2H₂O₂ $\rightarrow$ 2H₂O + O₂

A) 68.0 g $\rightarrow$ 36.0 g + 32.0 g
B) 34.0 g $\rightarrow$ 18.0 g + 16.0 g
C) 90.5 g $\rightarrow$ 47.9 g + 42.6 g
D) 2x g $\rightarrow$ 2x g + x g
E) y(34.0 g) $\rightarrow$ y(18.0 g) + (32 g)(y/2)

Question 23

Identify the list below that has these oxides arranged in order of increasing molar mass. Save time by looking at the periodic table and thinking, without actually doing any calculations.

A) SO₂ < NO₂ < CO₂ < NO < CO
B) CO < NO < CO₂ < NO₂ < SO₂
C) CO < CO₂ < NO < NO₂ < SO₂
D) NO < NO₂ < CO < CO₂ < SO₂
E) CO < NO < NO₂ < CO₂ < SO₂

Question 24

Fuming sulfuric acid is obtained by the addition of SO₃ to concentrated H₂SO₄. The fumes result from the reaction of SO₃ gas with water vapor. What is the product when one molecule of SO₃ reacts with one molecule of water?

A) two molecules of sulfurous acid
B) one sulfate ion
C) two sulfite ions
D) one molecule of sulfuric acid
E) two molecules of sulfuric acid

Question 25

In the summer of 2010, platinum (195.078 g/mol) sold for $1,500/oz. One ounce is equal to 28.35 g. How many platinum atoms could you buy with a penny ($0.01)?

A) 5.0 * 10²⁰ atoms
B) 2.6 F* 10⁶ atoms
C) 6.5 *10¹⁹ atoms
D) 1.5 *10¹⁸ atoms
E) 5.8 * 10¹⁷ atoms

Question 26

How many hydrogen atoms are there in a 346 g sample of pure ammonia (NH₃)?

A) 3.67 * 10²⁵ atoms
B) 1.22 * 10²⁵ atoms
C) 60.9 atoms
D) 20.3 atoms
E) 4.89 * 10²⁵ atoms

Question 27

As a purchasing agent for a pharmaceutical company, how much chlorine, Cl₂, do you need to order to react completely with 500 kg of platinum, Pt, to make cisplatin, PtCl₂(NH₃)₂?

A) 182 kg
B) 500 kg
C) 2,564 kg
D) 364 kg
E) 91 kg

Question 28

How many oxygen atoms are there in 27.0 g of sodium sulfate (Na₂SO₄)?

A) 1.15 * 10²³ atoms
B) 4.58 *10²³ atoms
C) 5.73 * 10²³ atoms
D) 2.41 * 10²⁴ atoms
E) 6.88 * 10²³ atoms

Question 29

Which statement about the following chemical reaction is not correct?
2H₂ + O₂ $\rightarrow$ 2H₂O

A) It requires 1 mol of dioxygen to produce 2 mol of water.
B) It requires 2 mol of dihydrogen to produce 2 mol of water.
C) One mole of dioxygen reacts with 2 mol of dihydrogen.
D) Two moles of dioxygen react with dihydrogen to produce 2 mol of water.
E) Four moles of hydrogen atoms combine with 2 mol of oxygen atoms to produce 2 mol of water.

Question 30

What is the molar mass of phosphorus pentachloride (PCl₅)?

A) 177.25 g/mol
B) 190.30 g/mol
C) 208.22 g/mol
D) 172.75 g/mol
E) 202.82 g/mol

Question 31

A balanced chemical reaction equation is to a reactant as __________

A) a map is to a gas station.
B) a child is to a parent.
C) a recipe is to an ingredient.
D) a good job is to a college degree.
E) a paycheck is to a job.

Question 32

Which statement about a balanced chemical reaction equation is always correct?

A) The total number of moles of the products equals the total number of moles of the reactants.
B) The number of atoms of each kind is the same for the products as for the reactants.
C) The sum of the stoichiometric coefficients for the products equals the sum of the stoichiometric coefficients for the reactants.
D) The sum of the masses of gaseous reactants equals the sum of the masses of gaseous products.
E) The sum of the masses of solid products equals the sum of the masses of solid reactants.

Question 33

Air bags in cars inflate when an electrical spark activates sodium azide (NaN₃) so that it decomposes to sodium metal, Na, and nitrogen gas, N₂. In the balanced reaction equation, how many moles of nitrogen gas are formed for each mole of sodium azide?

A) 1
B) 1.5
C) 2
D) 3
E) 2.5

Question 34

Fe₂O₃(s) and powdered aluminum can react with great output of heat to form molten iron and Al₂O₃. When this reaction equation is balanced, what are the stoichiometric coefficients in the following order: Fe₂O₃, Al, Fe, Al₂O₃?

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

Question 35

What is the molar mass of sulfuric acid (H₂SO₄)?

A) 49.0 g/mol
B) 24.5 g/mol
C) 101 g/mol
D) 98.1 g/mol
E) 97.0 g/mol

Question 36

As a purchasing agent for a pharmaceutical company, you need to determine the amount of platinum that is needed per kilogram of cisplatin, which is an anticancer drug. The chemical formula for cisplatin is PtCl₂(NH₃)₂, and its molar mass is 301g/mol.

A) 324 g
B) 648 g
C) 64.8 g
D) 32.4 g
E) 200 g

Question 37

How many mL of C₁₆H₃₄ are needed to react with 0.050 mol O₂, assuming complete combustion occurs? The density of C₁₆H₃₄ is 0.80 g/mL.

A) 0.99 mL
B) 0.37 mL
C) 0.58 mL
D) 0.46 mL
E) 0.89 mL

Question 38

Hydrogen peroxide decomposes to produce water and oxygen. Which relationship regarding the quantities of reactants and products associated with this reaction is not correct?
2H₂O₂ $\rightarrow$ 2H₂O + O₂

A) 2 molecules $\rightarrow$ 2 molecules + 1 molecule
B) 2 mol $\rightarrow$ 2 mol + 1 mol
C) 68.0 g $\rightarrow$ 36.0 g + 32.0 g
D) 2x mo $\rightarrow$ 2x mol + x mol
E) y(34.0 g) $\rightarrow$ y(18.0 g) + y(32 g)

Question 39

How many hydrogen atoms are there in 36.0 g of water (H₂O)?

A) 2
B) 4
C) 6.02 *10²³
D) 1.20 *10²⁴
E) 2.41 *10²⁴

Question 40

Which statement about the following chemical reaction is not correct?
3H₂ + N₂ $\rightarrow$ 2NH₃

A) For every mole of nitrogen consumed, two moles of ammonia are produced.
B) For every two moles of nitrogen consumed, three moles of ammonia are produced.
C) For every three moles of hydrogen consumed, two moles of ammonia are produced.
D) For every two moles of ammonia produced, three moles of hydrogen are consumed.
E) Three moles of hydrogen will react with one mole of nitrogen to produce ammonia.

Question 41

Which statement, A-D, regarding photosynthesis is not correct?
In the process of photosynthesis __________

A) light energy is converted into carbon-based fuels.
B) oxygen is produced.
C) atmospheric carbon dioxide is consumed.
D) the sugar glucose is produced.
E) A-D are all correct.

Question 42

A fuel cell works on the same principle as a battery but is continually fed with fuel. In one fuel cell, methanol (CH₃OH) enters on one side of the unit, and air enters on the other side. Both circulate past electrodes, and a chemical reaction occurs that produces electricity, plus carbon dioxide and water as byproducts. Which balanced chemical reaction equation best represents the reaction that occurs in this fuel cell?

A) CH₃OH $\rightarrow$ CO₂ + H₂O
B) CH₃OH $\rightarrow$ CH₃ + OH
C) CH₃OH $\rightarrow$ CH₂ + H₂O
D) CH₃OH + O₂ $\rightarrow$ CO₂ + H₂O
E) 2CH₃OH + 3O₂ $\rightarrow$ 2CO₂ + 4H₂O

Question 43

One form of elemental sulfur is a ring of eight sulfur atoms. How many moles of molecular oxygen are consumed when one mole of this allotrope burns to make sulfur trioxide?

A) 3
B) 6
C) 12
D) 18
E) 24

Question 44

Ozone (O₃) reacts with iodide (I^-) and water to form iodine (I₂), hydroxide (OH^-), and oxygen (O₂). Balance the following reaction equation and report the sum of the stoichiometric coefficients.
O₃ + I^- + H₂O $\rightarrow$ I₂ + OH^- + O₂

A) 10
B) 6
C) 8
D) 12
E) 14

Question 45

The combustion of butane (C₄H₁₀) forms carbon dioxide and water. What is the stoichiometric coefficient for oxygen in the balanced equation when 1 mol of butane undergoes combustion?

A) 9
B) 13
C) $\frac { 13 } { 2 }$
D) $\frac { 9 } { 2 }$
E) 5

Question 46

Identify the set of stoichiometric coefficients that balances the reaction equation for the combustion of octane.
C₈H₁₈ + O₂ $\rightarrow$ CO₂ + H₂O

A) 1, 25, 8, 9
B) 1, 17, 8, 9
C) 2, 34, 16, 18
D) 2, 25, 16, 18
E) None of the above coefficients balance the reaction equation.

Question 47

In a demonstration of the complete combustion of propane (C₃H₈) with oxygen (O₂), several balloons were prepared with various proportions by volume of propane and oxygen. The loudest explosion occurred for the balloon with the correct stoichiometric proportions of the gases. Which balloon had the loudest explosion? Note that the number of molecules of a gas is proportional to the volume of the gas at a given pressure and temperature.

A) 1 portion propane to 1 portion oxygen
B) 1 portion propane to 3 portions oxygen
C) 1 portion propane to 4 portions oxygen
D) 1 portion propane to 5 portions oxygen
E) 2 portions propane to 3 portions oxygen

Question 48

Glucose (C₆H₁₂O₆) is oxidized by molecular oxygen to carbon dioxide and water. How many O₂ molecules are needed for each molecule of glucose that is oxidized?

A) 1
B) 2
C) 6
D) 12
E) 18

Question 49

The average adult exhales about 1.0 kg of carbon dioxide each day. How much oxygen is needed in metabolizing glucose (C₆H₁₂O₆, 180 g/mol) to make that much carbon dioxide?

A) 180 g
B) 1800 g
C) 360 g
D) 730 g
E) 1500 g

Question 50

Sulfur dioxide from coal-fired power plants combines with water in the atmosphere to produce acid rain. What is the product when one molecule of SO₂ reacts with one molecule of water?

A) two molecules of sulfurous acid
B) one sulfate ion
C) two sulfite ions
D) one molecule of sulfuric acid
E) one molecule of sulfurous acid

Question 51

The combustion of fossil fuels is the main anthropogenic source of carbon dioxide in the atmosphere. During the combustion of gasoline in automobile engines, oxygen reacts with hydrocarbons to produce carbon dioxide and water. Assume gasoline is octane (C₈H₁₈). Write the balanced reaction equation, and report the sum of the stoichiometric coefficients written as integers.

A) 55
B) 29
C) 31
D) 30
E) 61

Question 52

The acid-base reaction between phosphoric acid, H₃PO₄, and calcium hydroxide, Ca(OH)₂, yields water and calcium phosphate. For each mole of calcium phosphate produced by this reaction, how many moles of water are produced?

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

Question 53

Burning coal that contains sulfur releases sulfur dioxide gas into the atmosphere where it combines with water to form sulfurous and sulfuric acid, thereby producing acid rain. Assume sulfur in coal is in the form of pyrite (FeS₂(s)), which reacts with molecular oxygen to produce Fe₂O₃(s) and SO₂(g). Write the balanced equation for this reaction and report the sum of the stoichiometric coefficients, written as integers.

A) 16
B) 14
C) 23
D) 25
E) 18

Question 54

Baking soda (NaHCO₃, 84.0 g/mol) requires acids from other ingredients to generate the carbon dioxide needed to make bread rise. The following equation describes this reaction, where HB is some unspecified acid. If 20.4 g of baking soda are used in a recipe and enough acid is present for a complete reaction, how many moles of carbon dioxide are generated?
HB + NaHCO₃ $\rightarrow$ H₂O + CO₂ + NaB

A) 0.464 mol
B) 0.334 mol
C) 0.243 mol
D) 0.204 mol
E) 0.232 mol

Question 55

Diesel fuel for automobiles and trucks is a mixture of hydrocarbons that can be modeled by C₁₆H₃₄. Write the balanced reaction equation for the combustion of C₁₆H₃₄, and report the sum of the stoichiometric coefficients.

A) 4
B) 120
C) 76
D) 83
E) 117

Question 56

What are the stoichiometric coefficients for oxygen and water, respectively, in the balanced chemical reaction equation representing the combustion of butane (C₄H₁₀)?

A) 4, 5
B) 9, 5
C) 13, 10
D) $\frac { 9 } { 2 }$
, 10
E) 13, 5

Question 57

The combustion of ethanol (CH₃CH₂OH, 46.1 g/mol) results in the formation of water and carbon dioxide. How many grams of carbon dioxide are produced when 46.1 g of ethanol burns?

A) 88.0 g
B) 44.0 g
C) 176 g
D) 22.0 g
E) 11.0 g

Question 58

If the combustion of fossil fuels adds about 5 *10¹² kg of carbon to the atmosphere as CO₂ each year, how much oxygen is required to produce this amount of carbon dioxide?

A) about 1.3 *10¹² kg
B) about 1.3*10¹³ kg
C) about 2.6 *10¹² kg
D) about 2.6*10¹³ kg
E) about 6.7 * 10¹² kg

Question 59

Which statement, A-D, regarding the carbon cycle is not correct?

A) Petroleum, coal, and other carbon sediments are produced.
B) Respiration produces atmospheric carbon dioxide.
C) Water is a reactant in photosynthesis.
D) Forest fires are part of the carbon cycle.
E) A-D are all correct.

Question 60

Copper sulfate is a blue solid that is used to control algae growth. Solutions of copper sulfate that come in contact with the surface of galvanized (zinc-plated) steel pails undergo the following reaction that forms copper metal on the zinc surface. How many grams of zinc would react with 454 g (1 lb) of copper sulfate (160 g/mol)?
CuSO₄(aq) + Zn(s) $\rightarrow$ Cu(s) + ZnSO₄(aq)

A) 467 g
B) 186 g
C) 93 g
D) 234 g
E) 454 g

Question 61

How much CO₂ is produced by a car driven 20,000 mi in one year?
Assume the following:
• A car gets 20 mi/4.0 L of gasoline.
• Gasoline has the chemical formula of octane: C₈H₁₈.
• One liter of gasoline has a mass of 0.8 kg.
• Gasoline is completely burned to carbon dioxide and water.

A) 1,500 kg
B) 9,900 kg
C) 15,000 kg
D) 20,000 kg
E) 4,900 kg

Question 62

Which molecules shown below have the same empirical formula?

A) II, III, IV are the same.
B) Only II and III are the same.
C) Only I and III are the same.
D) I, II, and III are the same.
E) I & III are the same, and II & IV are the same.

Question 63

The space shuttle uses liquid hydrogen and liquid oxygen to produce thrust for liftoff in the following reaction. If the liquid oxygen supply is set to provide 420 kg/s during a launch, what does the rate of liquid hydrogen supply need to be in kilograms per second?
2H₂(l) + O₂(l) $\rightarrow$ 2H₂O(g)

A) 840 kg/s
B) 210 kg/s
C) 106 kg/s
D) 52.9 kg/s
E) 63.4 kg/s

Question 64

The average adult exhales about 1.0 kg of carbon dioxide each day. How much glucose (C₆H₁₂O₆, 180 g/mol) is consumed to make that much carbon dioxide?

A) 3.8 kg
B) 4.1 kg
C) 0.43 kg
D) 0.68 kg
E) 0.18 kg

Question 65

Elemental analysis of the soot produced by a candle flame shows that it is 7.75% H and 92.3% C by mass. What is the empirical formula of this hydrocarbon?

A) CH
B) CH₂
C) C₂H
D) CH₃
E) C₂H₃

Question 66

Even though lead is toxic, lead compounds were used in ancient times as white pigments in cosmetics. What is the percentage of lead by mass in lead(IV) carbonate, Pb(CO₃)₂?

A) 32.7%
B) 20.7%
C) 63.3%
D) 77.5%
E) 81.4%

Question 67

A compound known to contain platinum, nitrogen, and hydrogen was analyzed and found to contain 74.1% Pt and 21.3% N; the remainder was hydrogen. What is the empirical formula for the compound?

A) Pt(NH₃)₄
B) Pt(NH₃)₃
C) Pt₂(NH₃)₂
D) Pt(NH₄)₂
E) Pt(NH₃)₆

Question 68

Copper was the first metal to be produced from its ore because it is the easiest to smelt, that is, to refine by heating in the presence of carbon (hence the early occurrence of the Bronze Age). The ore was likely malachite [Cu₂(OH)₂CO₃]. What is the mass percent of copper in malachite?

A) 28.7%
B) 45.2%
C) 57.5%
D) 40.3%
E) 74.6%

Question 69

Metallic copper can be obtained from the mineral chalcocite (Cu₂S). What is the mass percent of copper in chalcocite?

A) 79.85%
B) 66.46%
C) 20.15%
D) 33.54%
E) 57.47%

Question 70

Which molecules shown below have the same mass percent composition?

A) II, III, IV are the same.
B) Only II and III are the same.
C) Only I and III are the same.
D) I, II, and III are the same.
E) I & III are the same, and II & IV are the same.

Question 71

Elemental analysis of the soot produced by a candle flame shows that it is 14.3% H and 85.7% C by mass. What is the empirical formula of this hydrocarbon?

A) CH
B) CH₂
C) C₂H
D) CH₃
E) C₂H₃

Question 72

Hydrogen peroxide (H₂O₂) decomposes catalytically in the presence of metal ions and enzymes called peroxidases. You may have noticed this reaction occurring if you use a drugstore solution of hydrogen peroxide as a mouthwash or antiseptic. If a 250 mL bottle of hydrogen peroxide solution containing 3.0% H₂O₂ (by mass) completely decomposes, how many liters of oxygen gas would it generate? Assume that 1 mol of gas occupies a volume of 22.4 L and that the density of the solution is 1.0 g/mL. The reaction is
2H₂O₂(aq) $\rightarrow$ 2H₂O(l) + O₂(g)

A) 2.5 L
B) 4.9 L
C) 9.9 L
D) 7.4 L
E) 0.22 L

Question 73

Arizona was the site of a 400,000-acre wildfire in June 2002. How much carbon dioxide was produced by this fire? Assume that the density of carbon on the acreage was 10 kg/m² and that 50% of the biomass burned (10,000 m² = 2.47 acre)

A) 3 *10¹⁰ kg
B) 3 * 10⁶ kg
C) 3 *10³⁰ kg
D) 3 * 10⁹ kg
E) 3 *10¹³ kg

Question 74

An intermetallic titanium compound is used for medical implants and high quality jewelry. The composition of this compound is 70.68% titanium, 19.92% aluminum, and 9.400% vanadium. The molar masses of these elements are 47.88, 26.98, and 50.94 g/mol, respectively. What is the empirical formula of this compound?

A) Ti₄AlV
B) Ti₆Al₂V
C) Ti₆Al₄V
D) Ti₈Al₄V
E) Ti₁₀Al₅V₂

Question 75

An iron ore, magnetite, contains only iron and oxygen. In refining 100.0 g of the ore, 72.35 g of iron are obtained. What is the empirical formula of the ore?

A) Fe₂O₃
B) FeO₂
C) Fe₂O₅
D) Fe₃O₄
E) FeO

Question 76

Baking ammonia or ammonium bicarbonate (NH₄HCO₃, 79.1 g/mol) is a leavening agent used in some older recipes. As it is heated, it breaks down into three gases: ammonia, water, and carbon dioxide. For each 20 g of baking ammonia heated (about 4 tsp), how many grams of carbon dioxide are produced?

A) 15 g
B) 7.5 g
C) 11 g
D) 22 g
E) 20 g

Question 77

The most abundant metal in Earth's crust is aluminum, found mostly in the form of clays. There are no economical routes for extracting aluminum from clay. However, bauxite ore, impure hydrated aluminum oxide, is found in hot humid regions, such as Australia, Guinea, and Brazil, and it can be purified and refined to make the metal. After the first purification step, hydrated aluminum oxide (Al₂O₃ . xH₂O) is obtained. When 100.0 g of this solid were heated, and the water driven off, 65.36 g of Al₂O₃ remained. How many water molecules (x in the molecular formula) were there in the hydrate?

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

Question 78

One form of asbestos called chrysotile is considered to be a human carcinogen. Mass analysis shows that the composition of chrysotile is 26.3% Mg, 20.2% Si, 1.45% H, and the remainder of the mass is oxygen. Determine the empirical formula of chrysotile.

A) MgSiHO₃
B) Mg₂Si₂H₂O₅
C) Mg₃Si₂H₄O₆
D) Mg₃Si₂H₄O₉
E) Mg₄Si₃H₅O₉

Question 79

Water can be separated into its elements according to the following equation by electrolysis. If 20.0 g of water is decomposed by this method, how much oxygen gas is produced?
2H₂O (l) $\rightarrow$ 2H₂(g) + O₂(g)

A) 17.8 g
B) 8.9 g
C) 35.6 g
D) 16.0 g
E) 10.0 g

Question 80

What mass of phosphoric acid (H₃PO₄, 98.0 g/mol) is produced from the reaction of 10.0 g of P₄O₁₀ (284 g/mol) with excess water?

A) 10.9 g
B) 40.0 g
C) 10.0 g
D) 13.8 g
E) 2.50 g