,CHEM 121 Module 4 Exam Foundations of General
Chemistry w/Lab | Portage | 26/27 Actual (PDF)
1. What is the formula mass of calcium nitrate, Ca(NO₃)₂?
A) 102.09 amu
B) 164.09 amu
C) 132.09 amu
D) 116.09 amu
Correct Answer: 164.09 amu
Rationale: Formula mass = 1(Ca) + 2(N) + 6(O) = 40.08 + 2(14.01) + 6(16.00) = 40.08 + 28.02 + 96.00 =
164.10 amu. Option A omits the nitrate contribution, option C uses only one nitrogen, and option D
miscalculates oxygen atoms. Options A, C, and D are incorrect.
2. How many moles of oxygen atoms are present in 3.0 moles of Al₂(SO₄)₃?
A) 12 moles
B) 3.0 moles
C) 36 moles
D) 18 moles
Correct Answer: 36 moles
Rationale: Each formula unit of Al₂(SO₄)₃ contains 12 oxygen atoms (3 × 4 = 12). Therefore, 3.0 moles
of the compound contain 3.0 × 12 = 36 moles of oxygen atoms. Options A, B, and D are incorrect
because they do not account for the total number of oxygen atoms per formula unit.
3. A compound is composed of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its
empirical formula?
,A) C₂H₄O
B) CH₂O
C) C₂H₆O
D) CHO
Correct Answer: CH₂O
Rationale: Assuming 100 g, moles: C = 40.0/12.01 = 3.33, H = 6.7/1.008 = 6.65, O = 53.3/16.00 = 3.33.
Dividing by the smallest (3.33) gives C: 1, H: 2, O: 1, so the empirical formula is CH₂O. Options A, C, and
D have incorrect ratios.
4. What is the molarity of a solution prepared by dissolving 25.0 g of NaCl (molar mass = 58.44 g/mol)
in enough water to make 500.0 mL of solution?
A) 0.428 M
B) 0.856 M
C) 2.14 M
D) 0.214 M
Correct Answer: 0.856 M
Rationale: Moles of NaCl = 25.0 g / 58.44 g/mol = 0.428 mol. Volume = 0.5000 L. Molarity = 0.428
mol / 0.5000 L = 0.856 M. Option A is the number of moles, option C is double the correct value, and
option D is half the correct value.
5. When the following equation is balanced with the smallest whole-number coefficients, what is the
coefficient of O₂? __ C₃H₈ + __ O₂ → __ CO₂ + __ H₂O
A) 5
B) 7
, C) 3
D) 4
Correct Answer: 5
Rationale: Balancing C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O gives coefficients 1, 5, 3, 4. The coefficient of O₂ is 5.
Options B, C, and D do not satisfy the conservation of mass for this combustion reaction.
6. Which of the following is a precipitation reaction?
A) HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
B) 2 H₂(g) + O₂(g) → 2 H₂O(g)
C) AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
D) Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Correct Answer: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
Rationale: A precipitation reaction produces an insoluble solid (precipitate) from aqueous reactants.
AgCl(s) is the precipitate in option C. Option A is acid-base neutralization, option B is a synthesis
reaction, and option D is a single-replacement redox reaction.
7. What is the oxidation state of manganese in KMnO₄?
A) +2
B) +4
C) +7
D) +6
Correct Answer: +7
Chemistry w/Lab | Portage | 26/27 Actual (PDF)
1. What is the formula mass of calcium nitrate, Ca(NO₃)₂?
A) 102.09 amu
B) 164.09 amu
C) 132.09 amu
D) 116.09 amu
Correct Answer: 164.09 amu
Rationale: Formula mass = 1(Ca) + 2(N) + 6(O) = 40.08 + 2(14.01) + 6(16.00) = 40.08 + 28.02 + 96.00 =
164.10 amu. Option A omits the nitrate contribution, option C uses only one nitrogen, and option D
miscalculates oxygen atoms. Options A, C, and D are incorrect.
2. How many moles of oxygen atoms are present in 3.0 moles of Al₂(SO₄)₃?
A) 12 moles
B) 3.0 moles
C) 36 moles
D) 18 moles
Correct Answer: 36 moles
Rationale: Each formula unit of Al₂(SO₄)₃ contains 12 oxygen atoms (3 × 4 = 12). Therefore, 3.0 moles
of the compound contain 3.0 × 12 = 36 moles of oxygen atoms. Options A, B, and D are incorrect
because they do not account for the total number of oxygen atoms per formula unit.
3. A compound is composed of 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is its
empirical formula?
,A) C₂H₄O
B) CH₂O
C) C₂H₆O
D) CHO
Correct Answer: CH₂O
Rationale: Assuming 100 g, moles: C = 40.0/12.01 = 3.33, H = 6.7/1.008 = 6.65, O = 53.3/16.00 = 3.33.
Dividing by the smallest (3.33) gives C: 1, H: 2, O: 1, so the empirical formula is CH₂O. Options A, C, and
D have incorrect ratios.
4. What is the molarity of a solution prepared by dissolving 25.0 g of NaCl (molar mass = 58.44 g/mol)
in enough water to make 500.0 mL of solution?
A) 0.428 M
B) 0.856 M
C) 2.14 M
D) 0.214 M
Correct Answer: 0.856 M
Rationale: Moles of NaCl = 25.0 g / 58.44 g/mol = 0.428 mol. Volume = 0.5000 L. Molarity = 0.428
mol / 0.5000 L = 0.856 M. Option A is the number of moles, option C is double the correct value, and
option D is half the correct value.
5. When the following equation is balanced with the smallest whole-number coefficients, what is the
coefficient of O₂? __ C₃H₈ + __ O₂ → __ CO₂ + __ H₂O
A) 5
B) 7
, C) 3
D) 4
Correct Answer: 5
Rationale: Balancing C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O gives coefficients 1, 5, 3, 4. The coefficient of O₂ is 5.
Options B, C, and D do not satisfy the conservation of mass for this combustion reaction.
6. Which of the following is a precipitation reaction?
A) HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)
B) 2 H₂(g) + O₂(g) → 2 H₂O(g)
C) AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
D) Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
Correct Answer: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
Rationale: A precipitation reaction produces an insoluble solid (precipitate) from aqueous reactants.
AgCl(s) is the precipitate in option C. Option A is acid-base neutralization, option B is a synthesis
reaction, and option D is a single-replacement redox reaction.
7. What is the oxidation state of manganese in KMnO₄?
A) +2
B) +4
C) +7
D) +6
Correct Answer: +7
