Avogadro’s number (N_A)

experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 $\times$ 10^23 mol^−1

sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass

mass in grams of 1 mole of a substance

amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of ^12C

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Chemistry 2e · 3.1 Formula Mass and the Mole Concept

Formula Mass and the Mole Concept: practice problems

16 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1
What is the total mass (amu) of carbon in each of the following molecules?
(a) CH₄
(b) CHCl₃
(c) C₁₂H₁₀O₆
(d) CH₃CH₂CH₂CH₂CH₃
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Exercises 3
Calculate the molecular or formula mass of each of the following:
(a) P₄
(b) H₂O
(c) Ca(NO₃)₂
(d) CH₃CO₂H (acetic acid)
(e) C₁₂H₂₂O₁₁ (sucrose, cane sugar)
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Exercises 5
Determine the molecular mass of the following compounds:
(a)
(b)
(c)
(d)
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Exercises 7
Write a sentence that describes how to determine the number of moles of a compound in a known mass of the compound using its molecular formula.
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Exercises 9
Which contains the greatest mass of oxygen: 0.75 mol of ethanol (C₂H₅OH), 0.60 mol of formic acid (HCO₂H), or 1.0 mol of water (H₂O)? Explain why.
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Exercises 11
How are the molecular mass and the molar mass of a compound similar and how are they different?
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Exercises 13
Calculate the molar mass of each of the following:
(a) S₈
(b) C₅H₁₂
(c) Sc₂(SO₄)₃
(d) CH₃COCH₃ (acetone)
(e) C₆H₁₂O₆ (glucose)
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Exercises 15
Calculate the molar mass of each of the following:
(a) the anesthetic halothane, C₂HBrClF₃
(b) the herbicide paraquat, C₁₂H₁₄N₂Cl₂
(c) caffeine, C₈H₁₀N₄O₂
(d) urea, CO(NH₂)₂
(e) a typical soap, C₁₇H₃₅CO₂Na
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Exercises 17
Determine the mass of each of the following:
(a) 0.0146 mol KOH
(b) 10.2 mol ethane, C₂H₆
(c) 1.6 $\times$ 10⁻³ mol Na₂ SO₄
(d) 6.854 $\times$ 10³ mol glucose, C₆ H₁₂ O₆
(e) 2.86 mol Co(NH₃)₆Cl₃
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Exercises 19
Determine the mass of each of the following:
(a) 2.345 mol LiCl
(b) 0.0872 mol acetylene, C₂H₂
(c) 3.3 $\times$ 10⁻² mol Na₂CO₃
(d) 1.23 $\times$ 10³ mol fructose, C₆H₁₂O₆
(e) 0.5758 mol FeSO₄(H₂O)₇
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Exercises 21
Determine the mass in grams of each of the following:
(a) 0.600 mol of oxygen atoms
(b) 0.600 mol of oxygen molecules, O₂
(c) 0.600 mol of ozone molecules, O₃
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Exercises 23
Determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon, ZrSiO₄, a semiprecious stone.
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Exercises 25
Determine which of the following contains the greatest mass of aluminum: 122 g of AlPO₄, 266 g of Al₂Cl₆, or 225 g of Al₂S₃.
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Exercises 27
The Cullinan diamond was the largest natural diamond ever found (January 25, 1905). It weighed 3104 carats (1 carat = 200 mg). How many carbon atoms were present in the stone?
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Exercises 29
A certain nut crunch cereal contains 11.0 grams of sugar (sucrose, C₁₂H₂₂O₁₁) per serving size of 60.0 grams. How many servings of this cereal must be eaten to consume 0.0278 moles of sugar?
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Exercises 31
Which of the following represents the least number of molecules?
(a) 20.0 g of H₂O (18.02 g/mol)
(b) 77.0 g of CH₄ (16.06 g/mol)
(c) 68.0 g of C₃H₆ (42.08 g/mol)
(d) 100.0 g of N₂O (44.02 g/mol)
(e) 84.0 g of HF (20.01 g/mol)
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Key terms · 4

Avogadro’s number (N_A): experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 $\times$ 10^23 mol^−1
formula mass: sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass
molar mass: mass in grams of 1 mole of a substance
mole: amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of ^12C

Learn 3.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 3.1 in the textbook · This section on openstax.org

Formula Mass and the Mole Concept: practice problems

16 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 1

What is the total mass (amu) of carbon in each of the following molecules?

(a) CH₄

(b) CHCl₃

(d) CH₃CH₂CH₂CH₂CH₃

Exercises 3

Calculate the molecular or formula mass of each of the following:

(a) P₄

(b) H₂O

(d) CH₃CO₂H (acetic acid)

(e) C₁₂H₂₂O₁₁ (sucrose, cane sugar)

Exercises 5

Determine the molecular mass of the following compounds:

(a)

A structure is shown. Two C atoms form double bonds with each other. The C atom on the left forms a single bond with two H atoms each. The C atom on the right forms a single bond with an H atom and with a C H subscript 2 C H subscript 3 group.

(b)

A structure is shown. There is a C atom which forms single bonds with three H atoms each. This C atom is bonded to another C atom. This second C atom forms a triple bond with another C atom which forms a single bond with a fourth C atom. The fourth C atom forms single bonds with three H atoms each.

(c)

A structure is shown. An S i atom forms a single bond with a C l atom, a single bond with a C l atom, a single bond with an H atom, and a single bond with another S i atom. The second S i atom froms a single bond with a C l atom, a single bond with a C l atom, and a single bond with an H atom.

(d)

A structure is shown. A P atom forms a double bond with an O atom. It also forms a single bond with an O atom which forms a single bond with an H atom. It also forms a single bond with another O atom which forms a single bond with an H atom. It also forms a single bond with another O atom which forms a single bond with an H atom.

Exercises 7

Write a sentence that describes how to determine the number of moles of a compound in a known mass of the compound using its molecular formula.

Exercises 9

Which contains the greatest mass of oxygen: 0.75 mol of ethanol (C₂H₅OH), 0.60 mol of formic acid (HCO₂H), or 1.0 mol of water (H₂O)? Explain why.

Exercises 11

How are the molecular mass and the molar mass of a compound similar and how are they different?

Exercises 13

Calculate the molar mass of each of the following:

(a) S₈

(b) C₅H₁₂

(d) CH₃COCH₃ (acetone)

(e) C₆H₁₂O₆ (glucose)

Exercises 15

Calculate the molar mass of each of the following:

(a) the anesthetic halothane, C₂HBrClF₃

(b) the herbicide paraquat, C₁₂H₁₄N₂Cl₂

(d) urea, CO(NH₂)₂

(e) a typical soap, C₁₇H₃₅CO₂Na

Exercises 17

Determine the mass of each of the following:

(a) 0.0146 mol KOH

(b) 10.2 mol ethane, C₂H₆

(d) 6.854 $\times$ 10³ mol glucose, C₆ H₁₂ O₆

(e) 2.86 mol Co(NH₃)₆Cl₃

Exercises 19

Determine the mass of each of the following:

(a) 2.345 mol LiCl

(b) 0.0872 mol acetylene, C₂H₂

(d) 1.23 $\times$ 10³ mol fructose, C₆H₁₂O₆

(e) 0.5758 mol FeSO₄(H₂O)₇

Exercises 21

Determine the mass in grams of each of the following:

(a) 0.600 mol of oxygen atoms

(b) 0.600 mol of oxygen molecules, O₂

Exercises 23

Determine the number of atoms and the mass of zirconium, silicon, and oxygen found in 0.3384 mol of zircon, ZrSiO₄, a semiprecious stone.

Exercises 25

Determine which of the following contains the greatest mass of aluminum: 122 g of AlPO₄, 266 g of Al₂Cl₆, or 225 g of Al₂S₃.

Exercises 27

The Cullinan diamond was the largest natural diamond ever found (January 25, 1905). It weighed 3104 carats (1 carat = 200 mg). How many carbon atoms were present in the stone?

Exercises 29

A certain nut crunch cereal contains 11.0 grams of sugar (sucrose, C₁₂H₂₂O₁₁) per serving size of 60.0 grams. How many servings of this cereal must be eaten to consume 0.0278 moles of sugar?

Exercises 31

Which of the following represents the least number of molecules?

(a) 20.0 g of H₂O (18.02 g/mol)

(b) 77.0 g of CH₄ (16.06 g/mol)

(d) 100.0 g of N₂O (44.02 g/mol)

(e) 84.0 g of HF (20.01 g/mol)

Key terms · 4

Avogadro’s number (N_A): experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 $\times$ 10^23 mol^−1
formula mass: sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass
molar mass: mass in grams of 1 mole of a substance
mole: amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of ^12C

Learn 3.1 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 3.1 in the textbook · This section on openstax.org