CHEMISTRY MIDTERM REVIEW Q&A
General Chemistry Concepts
Question 1
What is the correct electron configuration for a neutral oxygen atom (atomic
number 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
Answer: A. 1s² 2s² 2p⁴
Rationale: Oxygen has 8 electrons. The electron configuration fills orbitals in order of
increasing energy: 1s (2 electrons), 2s (2 electrons), and 2p (4 electrons). The 2p subshell
can hold up to 6 electrons, but oxygen only has 4, giving 1s²2s²2p⁴. Option B is neon (10
electrons).
Question 2
Which of the following represents an isotope of carbon-12?
,A. Carbon-14 with 6 protons and 8 neutrons
B. Carbon-12 with 6 protons and 6 neutrons
C. Carbon-13 with 6 protons and 7 neutrons
D. All of the above
Answer: D. All of the above
Rationale: Isotopes are atoms of the same element with the same number of protons
but different numbers of neutrons. Carbon always has 6 protons. Carbon-12 has 6
neutrons, carbon-13 has 7 neutrons, and carbon-14 has 8 neutrons. All are isotopes of
carbon.
Question 3
What is the molar mass of water (H₂O)? (H=1.008, O=15.999)
A. 16.00 g/mol
B. 17.01 g/mol
C. 18.02 g/mol
D. 19.00 g/mol
Answer: C. 18.02 g/mol
Rationale: Molar mass = (2 × 1.008) + 15.999 = 2.016 + 15.999 = 18.015 g/mol,
approximately 18.02 g/mol.
Question 4
How many moles are in 36.04 grams of water?
A. 1.0 mol
B. 2.0 mol
C. 3.0 mol
D. 4.0 mol
Answer: B. 2.0 mol
, Rationale: Moles = mass/molar mass. Molar mass of H₂O = 18.02 g/mol. 36.04 g ÷
18.02 g/mol = 2.0 mol.
Question 5
Which of the following compounds contains an ionic bond?
A. CO₂
B. NaCl
C. H₂O
D. CH₄
Answer: B. NaCl
Rationale: NaCl (sodium chloride) is formed by the transfer of electrons from sodium (a
metal) to chlorine (a nonmetal), resulting in an ionic bond. CO₂, H₂O, and CH₄ are
covalent compounds formed by sharing electrons between nonmetals.
Question 6
What is the charge of an alpha particle?
A. -1
B. 0
C. +2
D. +1
Answer: C. +2
Rationale: An alpha particle consists of 2 protons and 2 neutrons (essentially a helium
nucleus) and carries a +2 charge due to the two protons.
General Chemistry Concepts
Question 1
What is the correct electron configuration for a neutral oxygen atom (atomic
number 8)?
A. 1s² 2s² 2p⁴
B. 1s² 2s² 2p⁶
C. 1s² 2s² 2p³
D. 1s² 2s² 2p⁵
Answer: A. 1s² 2s² 2p⁴
Rationale: Oxygen has 8 electrons. The electron configuration fills orbitals in order of
increasing energy: 1s (2 electrons), 2s (2 electrons), and 2p (4 electrons). The 2p subshell
can hold up to 6 electrons, but oxygen only has 4, giving 1s²2s²2p⁴. Option B is neon (10
electrons).
Question 2
Which of the following represents an isotope of carbon-12?
,A. Carbon-14 with 6 protons and 8 neutrons
B. Carbon-12 with 6 protons and 6 neutrons
C. Carbon-13 with 6 protons and 7 neutrons
D. All of the above
Answer: D. All of the above
Rationale: Isotopes are atoms of the same element with the same number of protons
but different numbers of neutrons. Carbon always has 6 protons. Carbon-12 has 6
neutrons, carbon-13 has 7 neutrons, and carbon-14 has 8 neutrons. All are isotopes of
carbon.
Question 3
What is the molar mass of water (H₂O)? (H=1.008, O=15.999)
A. 16.00 g/mol
B. 17.01 g/mol
C. 18.02 g/mol
D. 19.00 g/mol
Answer: C. 18.02 g/mol
Rationale: Molar mass = (2 × 1.008) + 15.999 = 2.016 + 15.999 = 18.015 g/mol,
approximately 18.02 g/mol.
Question 4
How many moles are in 36.04 grams of water?
A. 1.0 mol
B. 2.0 mol
C. 3.0 mol
D. 4.0 mol
Answer: B. 2.0 mol
, Rationale: Moles = mass/molar mass. Molar mass of H₂O = 18.02 g/mol. 36.04 g ÷
18.02 g/mol = 2.0 mol.
Question 5
Which of the following compounds contains an ionic bond?
A. CO₂
B. NaCl
C. H₂O
D. CH₄
Answer: B. NaCl
Rationale: NaCl (sodium chloride) is formed by the transfer of electrons from sodium (a
metal) to chlorine (a nonmetal), resulting in an ionic bond. CO₂, H₂O, and CH₄ are
covalent compounds formed by sharing electrons between nonmetals.
Question 6
What is the charge of an alpha particle?
A. -1
B. 0
C. +2
D. +1
Answer: C. +2
Rationale: An alpha particle consists of 2 protons and 2 neutrons (essentially a helium
nucleus) and carries a +2 charge due to the two protons.
