,CHEM 103 Module 4 Exam | General
Chemistry I w/Lab | Portage Learning | Q & A
| 2026 Edition
1. Which of the following best defines the mole in chemistry?
A) A unit of mass equal to 1 gram
B) The amount of substance that contains as many particles as there are atoms in exactly 12 grams of
carbon-12
C) The volume occupied by one gram of a substance at STP
D) The number of atoms in one liter of any gas at STP
Correct Answer: The amount of substance that contains as many particles as there are atoms in exactly
12 grams of carbon-12
Rationale: The mole is the SI base unit for the amount of substance. It is defined as the quantity
containing exactly 6.022 × 10²³ entities (Avogadro's number), which is the number of atoms in 12 grams
of pure carbon-12. This definition links the microscopic world of atoms to macroscopic measurable
quantities.
2. What is Avogadro's number?
A) 6.022 × 10²²
B) 6.022 × 10²³
C) 6.022 × 10²⁴
D) 6.022 × 10²¹
Correct Answer: 6.022 × 10²³
Rationale: Avogadro's number is 6.022 × 10²³ particles per mole. It represents the number of atoms,
molecules, or formula units in one mole of any substance. This constant is fundamental in converting
between the number of particles and the amount of substance in moles.
,3. How many atoms are present in exactly 2.00 moles of pure gold?
A) 1.20 × 10²⁴ atoms
B) 6.02 × 10²³ atoms
C) 3.01 × 10²³ atoms
D) 1.20 × 10²³ atoms
Correct Answer: 1.20 × 10²⁴ atoms
Rationale: Using Avogadro's number, 1 mole of any substance contains 6.022 × 10²³ particles. Therefore,
2.00 moles of gold contains 2.00 × 6.022 × 10²³ = 1.204 × 10²⁴ atoms, which rounds to 1.20 × 10²⁴ atoms.
4. What is the molar mass of sodium chloride (NaCl)?
A) 58.44 g/mol
B) 68.44 g/mol
C) 48.44 g/mol
D) 28.44 g/mol
Correct Answer: 58.44 g/mol
Rationale: The molar mass of NaCl is the sum of the atomic masses of sodium (Na = 22.99 g/mol) and
chlorine (Cl = 35.45 g/mol), which equals 58.44 g/mol. This value represents the mass of one mole of
NaCl formula units.
5. Calculate the molar mass of calcium phosphate, Ca₃(PO₄)₂.
A) 310.18 g/mol
B) 278.18 g/mol
C) 350.18 g/mol
D) 290.18 g/mol
Correct Answer: 310.18 g/mol
, Rationale: Molar mass = (3 × Ca) + (2 × P) + (8 × O) = (3 × 40.08) + (2 × 30.97) + (8 × 16.00) = 120.24 +
61.94 + 128.00 = 310.18 g/mol. This is the mass of one mole of calcium phosphate.
6. How many moles are present in 25.0 grams of sodium chloride (NaCl)?
A) 0.428 mole
B) 0.528 mole
C) 0.328 mole
D) 0.628 mole
Correct Answer: 0.428 mole
Rationale: Moles = mass (g) / molar mass (g/mol) = 25.0 g / 58.44 g/mol = 0.428 mole. This calculation is
essential for converting between mass and amount of substance.
7. What is the mass of 0.750 moles of carbon dioxide (CO₂)?
A) 33.0 g
B) 44.0 g
C) 22.0 g
D) 66.0 g
Correct Answer: 33.0 g
Rationale: The molar mass of CO₂ is 44.01 g/mol (C = 12.01, O = 16.00 × 2). Mass = moles × molar mass =
0.750 mol × 44.01 g/mol = 33.0 g. This demonstrates the conversion from moles to mass.
8. How many molecules are present in 0.500 moles of water (H₂O)?
A) 3.01 × 10²³ molecules
B) 6.02 × 10²³ molecules
C) 1.20 × 10²⁴ molecules
Chemistry I w/Lab | Portage Learning | Q & A
| 2026 Edition
1. Which of the following best defines the mole in chemistry?
A) A unit of mass equal to 1 gram
B) The amount of substance that contains as many particles as there are atoms in exactly 12 grams of
carbon-12
C) The volume occupied by one gram of a substance at STP
D) The number of atoms in one liter of any gas at STP
Correct Answer: The amount of substance that contains as many particles as there are atoms in exactly
12 grams of carbon-12
Rationale: The mole is the SI base unit for the amount of substance. It is defined as the quantity
containing exactly 6.022 × 10²³ entities (Avogadro's number), which is the number of atoms in 12 grams
of pure carbon-12. This definition links the microscopic world of atoms to macroscopic measurable
quantities.
2. What is Avogadro's number?
A) 6.022 × 10²²
B) 6.022 × 10²³
C) 6.022 × 10²⁴
D) 6.022 × 10²¹
Correct Answer: 6.022 × 10²³
Rationale: Avogadro's number is 6.022 × 10²³ particles per mole. It represents the number of atoms,
molecules, or formula units in one mole of any substance. This constant is fundamental in converting
between the number of particles and the amount of substance in moles.
,3. How many atoms are present in exactly 2.00 moles of pure gold?
A) 1.20 × 10²⁴ atoms
B) 6.02 × 10²³ atoms
C) 3.01 × 10²³ atoms
D) 1.20 × 10²³ atoms
Correct Answer: 1.20 × 10²⁴ atoms
Rationale: Using Avogadro's number, 1 mole of any substance contains 6.022 × 10²³ particles. Therefore,
2.00 moles of gold contains 2.00 × 6.022 × 10²³ = 1.204 × 10²⁴ atoms, which rounds to 1.20 × 10²⁴ atoms.
4. What is the molar mass of sodium chloride (NaCl)?
A) 58.44 g/mol
B) 68.44 g/mol
C) 48.44 g/mol
D) 28.44 g/mol
Correct Answer: 58.44 g/mol
Rationale: The molar mass of NaCl is the sum of the atomic masses of sodium (Na = 22.99 g/mol) and
chlorine (Cl = 35.45 g/mol), which equals 58.44 g/mol. This value represents the mass of one mole of
NaCl formula units.
5. Calculate the molar mass of calcium phosphate, Ca₃(PO₄)₂.
A) 310.18 g/mol
B) 278.18 g/mol
C) 350.18 g/mol
D) 290.18 g/mol
Correct Answer: 310.18 g/mol
, Rationale: Molar mass = (3 × Ca) + (2 × P) + (8 × O) = (3 × 40.08) + (2 × 30.97) + (8 × 16.00) = 120.24 +
61.94 + 128.00 = 310.18 g/mol. This is the mass of one mole of calcium phosphate.
6. How many moles are present in 25.0 grams of sodium chloride (NaCl)?
A) 0.428 mole
B) 0.528 mole
C) 0.328 mole
D) 0.628 mole
Correct Answer: 0.428 mole
Rationale: Moles = mass (g) / molar mass (g/mol) = 25.0 g / 58.44 g/mol = 0.428 mole. This calculation is
essential for converting between mass and amount of substance.
7. What is the mass of 0.750 moles of carbon dioxide (CO₂)?
A) 33.0 g
B) 44.0 g
C) 22.0 g
D) 66.0 g
Correct Answer: 33.0 g
Rationale: The molar mass of CO₂ is 44.01 g/mol (C = 12.01, O = 16.00 × 2). Mass = moles × molar mass =
0.750 mol × 44.01 g/mol = 33.0 g. This demonstrates the conversion from moles to mass.
8. How many molecules are present in 0.500 moles of water (H₂O)?
A) 3.01 × 10²³ molecules
B) 6.02 × 10²³ molecules
C) 1.20 × 10²⁴ molecules
