Define Avogadro's number .

Avogadro's number ( N A ) = 6.022 × 10 23 mol -1 . It is the number of particles in exactly one mole of any substance.

Why is the mole a useful unit for chemists?

Atoms, ions and molecules are too small to count directly in a lab. The mole allows chemists to work with measurable masses while knowing the exact number of particles present.

The number of particles in a sample equals .......... × the number of moles.

The number of particles in a sample equals Avogadro's number ( N A , 6.022 × 10 23 mol -1 ) × the number of moles.

True or False? One mole of H 2 O contains 6.022 × 10 23 hydrogen atoms.

False. One mole of H 2 O contains 6.022 × 10 23 molecules. Since each molecule has 2 H atoms, the sample actually contains 1.204 × 10 24 hydrogen atoms.

A student has 1.00 mol of Al 2 (SO 4 ) 3 . How many sulfate ions does it contain?

Each formula unit of Al 2 (SO 4 ) 3 contains 3 SO 4 2- ions. Number of SO 4 2- ions = 3 × 6.022 × 10 23 = 1.81 × 10 24 sulfate ions.

The mole (mol) is the SI unit for the amount of substance. One mole of any substance contains Avogadro's number (6.022 × 10 23 ) of particles.

Why is it important to specify the type of particle when working with the mole?

One mole always contains 6.022 × 10 23 formula units or molecules, but the number of atoms or ions differs by compound. For example, one mole of H 2 O contains 6.022 × 10 23 molecules but 1.807 × 10 24 individual atoms.

Molar mass ( M ) is the mass of one mole of a substance, expressed in g/mol. Its numerical value equals the atomic mass of the element or the sum of atomic masses in a compound.

True or False? The average atomic mass of carbon is 12.01 amu, so 1.00 mol of carbon has a mass of 12.01 g.

True. Atomic mass (amu) and molar mass (g/mol) are numerically equal — that is the definition of molar mass.

Why do atomic mass in amu and molar mass in g/mol share the same numerical value?

Avogadro's number was defined so that 12 g of carbon-12 contains exactly 6.022 × 10 23 atoms . This anchors atomic mass (amu per atom) to molar mass (g/mol per mole), making the two numbers identical for every element and compound.

The molar mass of SO 2 is .......... g/mol.

The molar mass of SO 2 is 64.06 g/mol. (S: 32.06 + 2 × O: 16.00 = 64.06 g/mol)

A student calculates the molar mass of Ca(C 2 H 3 O 2 ) 2 . What value should they obtain?

Ca: 40.08 + 4C: 48.04 + 6H: 6.048 + 4O: 64.00 = 158.17 g/mol . Always use atomic masses from the AP® periodic table for free response answers.

State the equation linking mass , moles , and molar mass .

n = m / M , where n = moles (mol), m = mass (g) and M = molar mass (g/mol). Rearranges to m = n × M or M = m / n .

How many moles are in a 42.0 g sample of C 6 H 14 (molar mass = 86.17 g/mol)?

n = m / M = 42.0 / 86.17 = 0.487 mol of C 6 H 14 .

True or False? A 86.17 g sample of C 6 H 14 contains 6.022 × 10 23 molecules.

True. A sample with mass equal to the molar mass always contains exactly Avogadro's number (6.022 × 10 23 ) of molecules — that is the definition of one mole.

Using the factor-label method, 42.0 g of C 6 H 14 is converted to moles by multiplying by .......... .

Using the factor-label method, 42.0 g of C 6 H 14 is converted to moles by multiplying by 1 mol / 86.17 g (the reciprocal of molar mass).

A student has 2.94 × 10 23 molecules of C 6 H 14 (molar mass = 86.17 g/mol). What is the mass of this sample?

Step 1 — moles: (2.94 × 10 23 ) ÷ (6.022 × 10 23 ) = 0.488 mol . Step 2 — mass: 0.488 × 86.17 = 42.1 g .

Define the factor-label method .

The factor-label method converts between units by multiplying by equivalent fractions so original units cancel and the target unit remains. For mole calculations: multiply grams by (1 mol / molar mass in g) to obtain moles.

A 4.60 g sample of ethanol (C 2 H 5 OH, molar mass = 46.07 g/mol) is analyzed. How many ethanol molecules does it contain?

Step 1 — moles: n = 4.60 / 46.07 = 0.0998 mol . Step 2 — molecules: 0.0998 × 6.022 × 10 23 = 6.01 × 10 22 ethanol molecules.

AP®ChemistryCollege BoardFlashcardsUnit 1: Atomic Structure & PropertiesMoles & Molar Mass

Moles & Molar Mass (College Board AP® Chemistry): Flashcards

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FrontThe Mole Concept
Define Avogadro's number.

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Cards in this collection (19)

Define Avogadro's number.
Avogadro's number (N_A) = 6.022 × 10²³ mol^-1. It is the number of particles in exactly one mole of any substance.
Why is the mole a useful unit for chemists?
Atoms, ions and molecules are too small to count directly in a lab. The mole allows chemists to work with measurable masses while knowing the exact number of particles present.
The number of particles in a sample equals .......... × the number of moles.
The number of particles in a sample equals Avogadro's number (N_A, 6.022 × 10²³ mol^-1) × the number of moles.
True or False?
One mole of H₂O contains 6.022 × 10²³ hydrogen atoms.
False.
One mole of H₂O contains 6.022 × 10²³ molecules. Since each molecule has 2 H atoms, the sample actually contains 1.204 × 10²⁴ hydrogen atoms.
A student has 1.00 mol of Al₂(SO₄)₃. How many sulfate ions does it contain?
Each formula unit of Al₂(SO₄)₃ contains 3 SO₄^2- ions.
Number of SO₄^2- ions = 3 × 6.022 × 10²³ = 1.81 × 10²⁴ sulfate ions.
Define the mole.
The mole (mol) is the SI unit for the amount of substance. One mole of any substance contains Avogadro's number (6.022 × 10²³) of particles.
Why is it important to specify the type of particle when working with the mole?
One mole always contains 6.022 × 10²³ formula units or molecules, but the number of atoms or ions differs by compound. For example, one mole of H₂O contains 6.022 × 10²³ molecules but 1.807 × 10²⁴ individual atoms.
Define molar mass.
Molar mass (M) is the mass of one mole of a substance, expressed in g/mol. Its numerical value equals the atomic mass of the element or the sum of atomic masses in a compound.
True or False?
The average atomic mass of carbon is 12.01 amu, so 1.00 mol of carbon has a mass of 12.01 g.
True.
Atomic mass (amu) and molar mass (g/mol) are numerically equal — that is the definition of molar mass.
Why do atomic mass in amu and molar mass in g/mol share the same numerical value?
Avogadro's number was defined so that 12 g of carbon-12 contains exactly 6.022 × 10²³ atoms. This anchors atomic mass (amu per atom) to molar mass (g/mol per mole), making the two numbers identical for every element and compound.
The molar mass of SO₂ is .......... g/mol.
The molar mass of SO₂ is 64.06 g/mol. (S: 32.06 + 2 × O: 16.00 = 64.06 g/mol)
A student calculates the molar mass of Ca(C₂H₃O₂)₂. What value should they obtain?
Ca: 40.08 + 4C: 48.04 + 6H: 6.048 + 4O: 64.00 = 158.17 g/mol.
Always use atomic masses from the AP® periodic table for free response answers.
State the equation linking mass, moles, and molar mass.
n = m / M, where n = moles (mol), m = mass (g) and M = molar mass (g/mol).
Rearranges to m = n × M or M = m / n.
How many moles are in a 42.0 g sample of C₆H₁₄ (molar mass = 86.17 g/mol)?
n = m / M = 42.0 / 86.17 = 0.487 mol of C₆H₁₄.
True or False?
A 86.17 g sample of C₆H₁₄ contains 6.022 × 10²³ molecules.
True.
A sample with mass equal to the molar mass always contains exactly Avogadro's number (6.022 × 10²³) of molecules — that is the definition of one mole.
Using the factor-label method, 42.0 g of C₆H₁₄ is converted to moles by multiplying by .......... .
Using the factor-label method, 42.0 g of C₆H₁₄ is converted to moles by multiplying by 1 mol / 86.17 g (the reciprocal of molar mass).
A student has 2.94 × 10²³ molecules of C₆H₁₄ (molar mass = 86.17 g/mol). What is the mass of this sample?
Step 1 — moles: (2.94 × 10²³) ÷ (6.022 × 10²³) = 0.488 mol.
Step 2 — mass: 0.488 × 86.17 = 42.1 g.
Define the factor-label method.
The factor-label method converts between units by multiplying by equivalent fractions so original units cancel and the target unit remains. For mole calculations: multiply grams by (1 mol / molar mass in g) to obtain moles.
A 4.60 g sample of ethanol (C₂H₅OH, molar mass = 46.07 g/mol) is analyzed. How many ethanol molecules does it contain?
Step 1 — moles: n = 4.60 / 46.07 = 0.0998 mol.
Step 2 — molecules: 0.0998 × 6.022 × 10²³ = 6.01 × 10²² ethanol molecules.

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