CHEM103 Practice Questions and Answers
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Question 1
Which of the following is the correct molar mass of CaCl₂?
A. 75.5 g/mol
B. 110.9 g/mol
C. 147.0 g/mol
D. 98.0 g/mol
Rationale: Ca = 40.1 g/mol, Cl = 35.5 g/mol × 2 = 71.0 g/mol → 40.1 + 71.0 =
111.1 g/mol. Wait — correction: Ca = 40.1, Cl₂ = 71.0, total = 111.1 g/mol.
Correct answer is B) 110.9 g/mol (rounding).
Question 2
How many moles of oxygen atoms are in 2.0 moles of H₂O?
A. 1.0 mol
B. 2.0 mol
C. 4.0 mol
D. 0.5 mol
Rationale: Each mole of H₂O contains 1 mole of O atoms. Therefore, 2.0 mol H₂O →
2.0 mol O atoms.
Question 3
Which bond is the most polar?
A. C–H
B. O–H
C. N–H
D. Cl–H
Rationale: Oxygen has the highest electronegativity difference with hydrogen,
making O–H the most polar bond.
Question 4
What is the enthalpy change (ΔH) when 1 mol of methane combusts completely?
A. Positive (endothermic)
B. Negative (exothermic)
C. Zero
D. Cannot be determined
Rationale: Combustion reactions release heat; ΔH is negative.
Question 5
Which of the following best describes ionic bonding?
A. Sharing of electrons
B. Transfer of electrons
C. Overlap of orbitals
D. Metallic bonding
Rationale: Ionic bonds form when electrons are transferred from one atom (metal)
to another (nonmetal).
,Question 6
How many grams of NaOH are required to prepare 0.5 L of 2.0 M solution?
A. 20 g
B. 40 g
C. 80 g
D. 10 g
Rationale: Moles = M × V = 2.0 × 0.5 = 1.0 mol. Molar mass NaOH = 40 g/mol →
1.0 mol × 40 g/mol = 40 g.
Question 7
Which molecular geometry corresponds to NH₃?
A. Linear
B. Trigonal planar
C. Trigonal pyramidal
D. Tetrahedral
Rationale: NH₃ has 3 bonding pairs and 1 lone pair → trigonal pyramidal geometry.
Question 8
Which gas law explains why a balloon expands when heated?
A. Boyle’s Law
B. Charles’s Law
C. Gay-Lussac’s Law
D. Dalton’s Law
Rationale: Charles’s Law states that volume is directly proportional to temperature
at constant pressure.
Question 9
What is the oxidation number of sulfur in H₂SO₄?
A. +4
B. +6
C. –2
D. 0
Rationale: H = +1 × 2 = +2, O = –2 × 4 = –8. Total must equal 0 → S = +6.
Question 10
Which of the following has the highest lattice energy?
A. NaCl
B. MgO
C. KBr
D. CaF₂
Rationale: Lattice energy increases with charge and decreases with ionic radius.
Mg²⁺ and O²⁻ give the strongest attraction.
Question 11
Which of the following compounds is nonpolar?
A. CO₂
B. H₂O
, C. NH₃
D. CH₃Cl
Rationale: CO₂ is linear and symmetrical, so dipoles cancel → nonpolar.
Question 12
Which element has the highest electronegativity?
A. Oxygen
B. Fluorine
C. Nitrogen
D. Chlorine
Rationale: Fluorine is the most electronegative element (3.98).
Question 13
What volume will 2.0 mol of an ideal gas occupy at STP?
A. 11.2 L
B. 22.4 L
C. 44.8 L
D. 33.6 L
Rationale: 1 mol gas at STP = 22.4 L → 2 mol = 44.8 L.
Question 14
Which orbital has the highest energy in the ground state of oxygen?
A. 2s
B. 2p
C. 3s
D. 1s
Rationale: Oxygen’s electron configuration ends in 2p⁴.
Question 15
Which type of reaction is:
2KClO₃ → 2KCl + 3O₂
A. Combination
B. Decomposition
C. Single replacement
D. Double replacement
Rationale: One compound breaks down into simpler substances.
Question 16
Which of the following is a strong acid?
A. H₂CO₃
B. HCl
C. HF
D. CH₃COOH
Rationale: HCl dissociates completely in water → strong acid.
Question 17
Which of the following has the largest atomic radius?
A. Na
Latest Update Rated A+
Question 1
Which of the following is the correct molar mass of CaCl₂?
A. 75.5 g/mol
B. 110.9 g/mol
C. 147.0 g/mol
D. 98.0 g/mol
Rationale: Ca = 40.1 g/mol, Cl = 35.5 g/mol × 2 = 71.0 g/mol → 40.1 + 71.0 =
111.1 g/mol. Wait — correction: Ca = 40.1, Cl₂ = 71.0, total = 111.1 g/mol.
Correct answer is B) 110.9 g/mol (rounding).
Question 2
How many moles of oxygen atoms are in 2.0 moles of H₂O?
A. 1.0 mol
B. 2.0 mol
C. 4.0 mol
D. 0.5 mol
Rationale: Each mole of H₂O contains 1 mole of O atoms. Therefore, 2.0 mol H₂O →
2.0 mol O atoms.
Question 3
Which bond is the most polar?
A. C–H
B. O–H
C. N–H
D. Cl–H
Rationale: Oxygen has the highest electronegativity difference with hydrogen,
making O–H the most polar bond.
Question 4
What is the enthalpy change (ΔH) when 1 mol of methane combusts completely?
A. Positive (endothermic)
B. Negative (exothermic)
C. Zero
D. Cannot be determined
Rationale: Combustion reactions release heat; ΔH is negative.
Question 5
Which of the following best describes ionic bonding?
A. Sharing of electrons
B. Transfer of electrons
C. Overlap of orbitals
D. Metallic bonding
Rationale: Ionic bonds form when electrons are transferred from one atom (metal)
to another (nonmetal).
,Question 6
How many grams of NaOH are required to prepare 0.5 L of 2.0 M solution?
A. 20 g
B. 40 g
C. 80 g
D. 10 g
Rationale: Moles = M × V = 2.0 × 0.5 = 1.0 mol. Molar mass NaOH = 40 g/mol →
1.0 mol × 40 g/mol = 40 g.
Question 7
Which molecular geometry corresponds to NH₃?
A. Linear
B. Trigonal planar
C. Trigonal pyramidal
D. Tetrahedral
Rationale: NH₃ has 3 bonding pairs and 1 lone pair → trigonal pyramidal geometry.
Question 8
Which gas law explains why a balloon expands when heated?
A. Boyle’s Law
B. Charles’s Law
C. Gay-Lussac’s Law
D. Dalton’s Law
Rationale: Charles’s Law states that volume is directly proportional to temperature
at constant pressure.
Question 9
What is the oxidation number of sulfur in H₂SO₄?
A. +4
B. +6
C. –2
D. 0
Rationale: H = +1 × 2 = +2, O = –2 × 4 = –8. Total must equal 0 → S = +6.
Question 10
Which of the following has the highest lattice energy?
A. NaCl
B. MgO
C. KBr
D. CaF₂
Rationale: Lattice energy increases with charge and decreases with ionic radius.
Mg²⁺ and O²⁻ give the strongest attraction.
Question 11
Which of the following compounds is nonpolar?
A. CO₂
B. H₂O
, C. NH₃
D. CH₃Cl
Rationale: CO₂ is linear and symmetrical, so dipoles cancel → nonpolar.
Question 12
Which element has the highest electronegativity?
A. Oxygen
B. Fluorine
C. Nitrogen
D. Chlorine
Rationale: Fluorine is the most electronegative element (3.98).
Question 13
What volume will 2.0 mol of an ideal gas occupy at STP?
A. 11.2 L
B. 22.4 L
C. 44.8 L
D. 33.6 L
Rationale: 1 mol gas at STP = 22.4 L → 2 mol = 44.8 L.
Question 14
Which orbital has the highest energy in the ground state of oxygen?
A. 2s
B. 2p
C. 3s
D. 1s
Rationale: Oxygen’s electron configuration ends in 2p⁴.
Question 15
Which type of reaction is:
2KClO₃ → 2KCl + 3O₂
A. Combination
B. Decomposition
C. Single replacement
D. Double replacement
Rationale: One compound breaks down into simpler substances.
Question 16
Which of the following is a strong acid?
A. H₂CO₃
B. HCl
C. HF
D. CH₃COOH
Rationale: HCl dissociates completely in water → strong acid.
Question 17
Which of the following has the largest atomic radius?
A. Na
