CHEM 121 Final Exam | General Chemistry I Exam
Q&A | Portage Learning
1. Which of the following best describes a homogeneous mixture?
A) A mixture with visibly different components that can be separated by filtration
B) A pure substance composed of two or more elements chemically combined
C) A mixture with uniform composition throughout, such as air in a sealed room
D) A substance that cannot be broken down into simpler substances by chemical
means
Correct Answer: A mixture with uniform composition throughout, such as air in a sealed
room
Rationale: A homogeneous mixture has a uniform composition throughout, meaning its
components are evenly distributed at the molecular level and cannot be visually
distinguished. Air is a classic example, as it is a uniform mixture of gases. A
heterogeneous mixture has visibly different components, a compound is a pure
substance, and an element cannot be broken down chemically.
2. How many significant figures are present in the measurement 0.004050 g?
A) 3
B) 4
C) 5
D) 6
Correct Answer: 4
Rationale: Leading zeros are never significant. The digits 4, 0, 5, and the trailing zero
after 5 are significant because the trailing zero comes after a decimal point and follows a
non-zero digit. Therefore, the measurement 0.004050 g has four significant figures: 4, 0,
5, and 0.
3. What is the mass in grams of 2.50 moles of calcium phosphate, Ca₃(PO₄)₂?
(Molar masses: Ca = 40.08 g/mol, P = 30.97 g/mol, O = 16.00 g/mol)
A) 310.18 g
B) 775.45 g
C) 124.07 g
D) 620.36 g
Correct Answer: 775.45 g
Rationale: The molar mass of Ca₃(PO₄)₂ is calculated as 3(40.08) + 2(30.97) + 8(16.00) =
120.24 + 61.94 + 128.00 = 310.18 g/mol. To find the mass of 2.50 moles, multiply the
molar mass by the number of moles: 2.50 mol × 310.18 g/mol = 775.45 g. The other
options result from incorrect multiplication or molar mass calculations.
, 4. A researcher is studying a compound and determines that it contains 40.0%
carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical
formula of this compound?
A) C₂H₄O₂
B) CH₂O
C) C₃H₆O₃
D) CH₄O
Correct Answer: CH₂O
Rationale: Assuming a 100 g sample: moles C = 40.0/12.01 = 3.33, moles H = 6.7/1.01 =
6.63, moles O = 53.3/16.00 = 3.33. Dividing each by the smallest value (3.33) gives C = 1,
H = 2, O = 1. The empirical formula is CH₂O. The other options are multiples of this
empirical formula.
5. Which of the following statements is part of the kinetic molecular theory of
gases?
A) Gas particles are strongly attracted to one another.
B) Gas particles occupy a significant fraction of the container volume.
C) Collisions between gas particles are perfectly elastic.
D) Gas particles continuously lose kinetic energy over time.
Correct Answer: Collisions between gas particles are perfectly elastic.
Rationale: The kinetic molecular theory assumes that collisions between gas particles
and with the container walls are perfectly elastic, meaning no net loss of kinetic energy.
The theory also assumes that gas particles have negligible volume and no attractive or
repulsive forces between them. Options A, B, and D contradict these fundamental
assumptions.
6. A gas occupies 3.00 L at 25°C and 1.00 atm. What volume will it occupy at 50°C
and 1.00 atm?
A) 1.50 L
B) 3.25 L
C) 6.00 L
D) 3.00 L
Correct Answer: 3.25 L
Rationale: Using Charles's Law (V₁/T₁ = V₂/T₂) at constant pressure: V₂ = V₁ × (T₂/T₁) =
3.00 L × (323 K / 298 K) ≈ 3.25 L. Temperatures must be converted to Kelvin before
calculation. Options A, C, and D do not result from the correct application of Charles's
Law.
7. What is the partial pressure of oxygen in a gas mixture if the total pressure is 760
mmHg and the mole fraction of O₂ is 0.21?
, A) 160 mmHg
B) 210 mmHg
C) 380 mmHg
D) 760 mmHg
Correct Answer: 160 mmHg
Rationale: According to Dalton's Law of Partial Pressures, the partial pressure of a gas is
its mole fraction multiplied by the total pressure: P_O₂ = 0.21 × 760 mmHg ≈ 160 mmHg.
Option B corresponds to a mole fraction of 0.28, option C to 0.50, and option D to a
mole fraction of 1.00.
8. According to Le Chatelier's principle, what happens when the pressure of a
system at equilibrium is increased for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
A) The equilibrium shifts to the left, producing more reactants.
B) The equilibrium shifts to the right, producing more ammonia.
C) The equilibrium position remains unchanged.
D) The reaction stops completely.
Correct Answer: The equilibrium shifts to the right, producing more ammonia.
Rationale: Increasing pressure favors the side of the reaction with fewer moles of gas.
The reactant side has 4 moles of gas (1 N₂ + 3 H₂), while the product side has 2 moles (2
NH₃). Therefore, the equilibrium shifts to the right to reduce the pressure, producing
more ammonia.
9. A reaction has an equilibrium constant K = 2.5 × 10⁻³. What does this value
indicate about the reaction at equilibrium?
A) Products are favored.
B) Reactants are favored.
C) The reaction is at equilibrium with equal concentrations.
D) The reaction is not spontaneous.
Correct Answer: Reactants are favored.
Rationale: An equilibrium constant much less than 1 (K << 1) indicates that at
equilibrium, the concentration of reactants is much greater than the concentration of
products, meaning the reactants are favored. If K were much greater than 1, products
would be favored. K = 1 would indicate roughly equal concentrations.
10. What is the correct expression for the equilibrium constant (Kc) for the reaction:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g)?
A) Kc = [SO₃]² / ([SO₂]²[O₂])
B) Kc = ([SO₂]²[O₂]) / [SO₃]²
C) Kc = [SO₃] / ([SO₂][O₂])
D) Kc = ([SO₂][O₂]) / [SO₃]
Q&A | Portage Learning
1. Which of the following best describes a homogeneous mixture?
A) A mixture with visibly different components that can be separated by filtration
B) A pure substance composed of two or more elements chemically combined
C) A mixture with uniform composition throughout, such as air in a sealed room
D) A substance that cannot be broken down into simpler substances by chemical
means
Correct Answer: A mixture with uniform composition throughout, such as air in a sealed
room
Rationale: A homogeneous mixture has a uniform composition throughout, meaning its
components are evenly distributed at the molecular level and cannot be visually
distinguished. Air is a classic example, as it is a uniform mixture of gases. A
heterogeneous mixture has visibly different components, a compound is a pure
substance, and an element cannot be broken down chemically.
2. How many significant figures are present in the measurement 0.004050 g?
A) 3
B) 4
C) 5
D) 6
Correct Answer: 4
Rationale: Leading zeros are never significant. The digits 4, 0, 5, and the trailing zero
after 5 are significant because the trailing zero comes after a decimal point and follows a
non-zero digit. Therefore, the measurement 0.004050 g has four significant figures: 4, 0,
5, and 0.
3. What is the mass in grams of 2.50 moles of calcium phosphate, Ca₃(PO₄)₂?
(Molar masses: Ca = 40.08 g/mol, P = 30.97 g/mol, O = 16.00 g/mol)
A) 310.18 g
B) 775.45 g
C) 124.07 g
D) 620.36 g
Correct Answer: 775.45 g
Rationale: The molar mass of Ca₃(PO₄)₂ is calculated as 3(40.08) + 2(30.97) + 8(16.00) =
120.24 + 61.94 + 128.00 = 310.18 g/mol. To find the mass of 2.50 moles, multiply the
molar mass by the number of moles: 2.50 mol × 310.18 g/mol = 775.45 g. The other
options result from incorrect multiplication or molar mass calculations.
, 4. A researcher is studying a compound and determines that it contains 40.0%
carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical
formula of this compound?
A) C₂H₄O₂
B) CH₂O
C) C₃H₆O₃
D) CH₄O
Correct Answer: CH₂O
Rationale: Assuming a 100 g sample: moles C = 40.0/12.01 = 3.33, moles H = 6.7/1.01 =
6.63, moles O = 53.3/16.00 = 3.33. Dividing each by the smallest value (3.33) gives C = 1,
H = 2, O = 1. The empirical formula is CH₂O. The other options are multiples of this
empirical formula.
5. Which of the following statements is part of the kinetic molecular theory of
gases?
A) Gas particles are strongly attracted to one another.
B) Gas particles occupy a significant fraction of the container volume.
C) Collisions between gas particles are perfectly elastic.
D) Gas particles continuously lose kinetic energy over time.
Correct Answer: Collisions between gas particles are perfectly elastic.
Rationale: The kinetic molecular theory assumes that collisions between gas particles
and with the container walls are perfectly elastic, meaning no net loss of kinetic energy.
The theory also assumes that gas particles have negligible volume and no attractive or
repulsive forces between them. Options A, B, and D contradict these fundamental
assumptions.
6. A gas occupies 3.00 L at 25°C and 1.00 atm. What volume will it occupy at 50°C
and 1.00 atm?
A) 1.50 L
B) 3.25 L
C) 6.00 L
D) 3.00 L
Correct Answer: 3.25 L
Rationale: Using Charles's Law (V₁/T₁ = V₂/T₂) at constant pressure: V₂ = V₁ × (T₂/T₁) =
3.00 L × (323 K / 298 K) ≈ 3.25 L. Temperatures must be converted to Kelvin before
calculation. Options A, C, and D do not result from the correct application of Charles's
Law.
7. What is the partial pressure of oxygen in a gas mixture if the total pressure is 760
mmHg and the mole fraction of O₂ is 0.21?
, A) 160 mmHg
B) 210 mmHg
C) 380 mmHg
D) 760 mmHg
Correct Answer: 160 mmHg
Rationale: According to Dalton's Law of Partial Pressures, the partial pressure of a gas is
its mole fraction multiplied by the total pressure: P_O₂ = 0.21 × 760 mmHg ≈ 160 mmHg.
Option B corresponds to a mole fraction of 0.28, option C to 0.50, and option D to a
mole fraction of 1.00.
8. According to Le Chatelier's principle, what happens when the pressure of a
system at equilibrium is increased for the reaction N₂(g) + 3H₂(g) ⇌ 2NH₃(g)?
A) The equilibrium shifts to the left, producing more reactants.
B) The equilibrium shifts to the right, producing more ammonia.
C) The equilibrium position remains unchanged.
D) The reaction stops completely.
Correct Answer: The equilibrium shifts to the right, producing more ammonia.
Rationale: Increasing pressure favors the side of the reaction with fewer moles of gas.
The reactant side has 4 moles of gas (1 N₂ + 3 H₂), while the product side has 2 moles (2
NH₃). Therefore, the equilibrium shifts to the right to reduce the pressure, producing
more ammonia.
9. A reaction has an equilibrium constant K = 2.5 × 10⁻³. What does this value
indicate about the reaction at equilibrium?
A) Products are favored.
B) Reactants are favored.
C) The reaction is at equilibrium with equal concentrations.
D) The reaction is not spontaneous.
Correct Answer: Reactants are favored.
Rationale: An equilibrium constant much less than 1 (K << 1) indicates that at
equilibrium, the concentration of reactants is much greater than the concentration of
products, meaning the reactants are favored. If K were much greater than 1, products
would be favored. K = 1 would indicate roughly equal concentrations.
10. What is the correct expression for the equilibrium constant (Kc) for the reaction:
2SO₂(g) + O₂(g) ⇌ 2SO₃(g)?
A) Kc = [SO₃]² / ([SO₂]²[O₂])
B) Kc = ([SO₂]²[O₂]) / [SO₃]²
C) Kc = [SO₃] / ([SO₂][O₂])
D) Kc = ([SO₂][O₂]) / [SO₃]
