AP CHEMISTRY EXAM TESTBANK| REVISED ALL QUESTIONS
AND ANSWERS 2026/2027 | VERIFIED ANSWERS PLUS
RATIONALES | GRADED Q&A COMPREHENSIVE STUDY GUIDE
| VERIFIED LATEST 2027
1. A laboratory technician massed an iron nail before and after exposure to air and water.
The final mass of the rusted nail was greater than the initial mass of the clean nail. Which
statement best explains this observation based on the Law of Conservation of Mass?
A. Mass was created during the chemical reaction when iron transformed into rust.
B. Iron atoms expanded in size due to oxidation, increasing the overall mass.
C. Oxygen atoms from the surrounding atmosphere reacted with the iron to form a compound.
D. The reaction was endothermic, absorbing energy that converted into measurable mass.
Answer: C
The Law of Conservation of Mass dictates that matter cannot be created or destroyed in a
chemical reaction. The increase in mass observed in the nail is due to gaseous oxygen
molecules from the air chemically combining with the solid iron atoms to form solid iron(III)
oxide. The missing mass in the initial measurement is accounted for by the atmospheric
oxygen consumed during the oxidation process.
2. A student measures the density of a pure aluminum block. The accepted density of
aluminum is 2.70 g/cm³. The student performs three trial measurements and records values
of 2.45 g/cm³, 2.46 g/cm³, and 2.45 g/cm³. Which statement correctly describes the student's
measurement results?
A. The measurements are both accurate and precise.
B. The measurements are precise but not accurate.
C. The measurements are accurate but not precise.
D. The measurements are neither accurate nor precise.
Answer: B
Precision refers to the closeness of agreement among repeated independent measurements,
while accuracy refers to the closeness of a measured value to a standard or accepted value.
The values (2.45, 2.46, 2.45) are clustered closely together, indicating high precision, but they
deviate significantly from the true accepted value of 2.70 g/cm³, indicating low accuracy.
3. Which of the following particulate diagrams best represents a pure element consisting of
diatomic molecules?
A. Single isolated spheres distributed uniformly throughout the container.
,B. Bound pairs of identical spheres distributed uniformly throughout the container.
C. Bound pairs of two distinct, differently shaded spheres throughout the container.
D. An alternating lattice arrangement of two differently sized spheres.
Answer: B
An element consists of only one type of atom. Diatomic elements (such as H2, N2, O2, F2, Cl2,
Br2, and I2) exist naturally as pairs of chemically bonded, identical atoms. Option B correctly
depicts single-element units composed of bound identical spheres, whereas Option A depicts a
monatomic element and Option C represents a binary molecular compound.
4. A sample of gas occupies 4.0 L at 2.0 atm. If the temperature remains constant, what will
be the new volume if the pressure is increased to 8.0 atm?
A. 1.0 L
B. 2.0 L
C. 8.0 L
D. 16.0 L
Answer: A
According to Boyle's Law (P1V1 = P2V2), pressure and volume are inversely proportional at
constant temperature and moles of gas. Solving for the new volume: V2 = (P1 * V1) / P2 = (2.0
atm * 4.0 L) / 8.0 atm = 1.0 L. Quadrupling the pressure results in reducing the volume to one-
fourth of its original size.
5. Which set of quantum numbers (n, l, ml, ms) is physically permissible for an electron in
an atom?
A. (2, 2, 0, +1/2)
B. (3, 1, -2, -1/2)
C. (4, 2, -1, +1/2)
D. (1, 0, 0, +1)
Answer: C
Quantum number rules dictate that n >= 1, l can range from 0 to (n - 1), ml can range from -l
to +l, and ms must be either +1/2 or -1/2. In Option C (4, 2, -1, +1/2), n=4 allows l=2 (d
orbital), l=2 allows ml=-1, and ms=+1/2 is valid. Option A is invalid because l cannot equal n.
Option B is invalid because ml cannot exceed l. Option D is invalid because ms cannot be +1.
6. A pure compound is analyzed and found to contain 40.0% carbon, 6.7% hydrogen, and
53.3% oxygen by mass. What is the empirical formula of the compound?
A. CH2O
B. C2H4O2
,C. C3H6O3
D. CHO
Answer: A
To find the empirical formula, convert mass percentages to moles assuming a 100g sample: C
= 40.0g / 12.01 g/mol = 3.33 mol; H = 6.7g / 1.008 g/mol = 6.65 mol; O = 53.3g / 16.00 g/mol
= 3.33 mol. Divide each mole quantity by the smallest value (3.33): C = 1, H = 2, O = 1. The
simplest whole-number ratio of atoms in the compound is CH2O.
7. Which of the following aqueous solutions will have the highest electrical conductivity at
room temperature?
A. 0.10 M C12H22O11 (sucrose)
B. 0.10 M CH3COOH (acetic acid)
C. 0.10 M NaCl (sodium chloride)
D. 0.10 M CaCl2 (calcium chloride)
Answer: D
Electrical conductivity in aqueous solutions depends on the concentration of mobile ions
present. Sucrose is a non-electrolyte (0 ions). Acetic acid is a weak acid that only partially
ionizes. Sodium chloride is a strong electrolyte yielding 2 moles of ions per mole of solute (Na+
and Cl-). Calcium chloride is a strong electrolyte yielding 3 moles of ions per mole of solute (1
Ca2+ and 2 Cl-), producing the highest total ion concentration (0.30 M total ions) and thus the
highest conductivity.
8. Under which conditions of temperature and pressure does a real gas deviate most
significantly from ideal behavior?
A. High temperature and low pressure
B. Low temperature and high pressure
C. High temperature and high pressure
D. Low temperature and low pressure
Answer: B
Real gases deviate from ideal behavior under conditions where intermolecular attractive
forces become significant and the volume occupied by gas molecules themselves is no longer
negligible relative to the total container volume. Low temperatures decrease molecular
kinetic energy, allowing intermolecular attractions to pull molecules together, while high
pressures force molecules into close proximity where their finite volume matters.
9. Which of the following electron configurations represents an atom in an excited state?
, A. 1s² 2s² 2p⁶ 3s²
B. 1s² 2s² 2p⁶ 3s¹ 3p¹
C. 1s² 2s² 2p⁵
D. 1s² 2s² 2p⁶ 3s² 3p⁴
Answer: B
An excited state occurs when an electron absorbs energy and transitions to a higher energy
orbital without filling the lower energy subshells according to the Aufbau principle. In
configuration B (1s² 2s² 2p⁶ 3s¹ 3p¹), one electron from the 3s subshell has been promoted to
the 3p subshell before the 3s orbital was fully occupied (which requires 3s²), indicating an
excited state.
10. What is the molecular geometry of the sulfur tetrafluoride (SF4) molecule?
A. Tetrahedral
B. Square planar
C. See-saw
D. Trigonal bipyramidal
Answer: C
Sulfur tetrafluoride (SF4) has 34 valence electrons. The central sulfur atom forms four single
bonds with fluorine atoms and retains one lone pair of electrons (AX4E notation). This results
in five electron domains around the central atom, giving a trigonal bipyramidal electron
domain geometry. Due to the equatorial placement of the single lone pair to minimize
electron repulsion, the spatial arrangement of the bonded atoms forms a see-saw molecular
geometry.
11. A student dissolves 10.0 g of potassium nitrate (KNO3) in 100.0 g of water at 25°C. The
temperature of the solution drops to 21.5°C. Which statement regarding the dissolution
process is correct?
A. The process is exothermic and ΔH is negative.
B. The process is endothermic and ΔH is positive.
C. The process is exothermic and ΔH is positive.
D. The process is endothermic and ΔH is negative.
Answer: B
A drop in temperature of the aqueous system indicates that heat energy was absorbed from
the surrounding water to break the ionic lattice interactions and solute-solute bonds. Because
the system absorbs energy from its surroundings, the process is classified as endothermic,
which is represented mathematically by a positive enthalpy change (+ΔH).
AND ANSWERS 2026/2027 | VERIFIED ANSWERS PLUS
RATIONALES | GRADED Q&A COMPREHENSIVE STUDY GUIDE
| VERIFIED LATEST 2027
1. A laboratory technician massed an iron nail before and after exposure to air and water.
The final mass of the rusted nail was greater than the initial mass of the clean nail. Which
statement best explains this observation based on the Law of Conservation of Mass?
A. Mass was created during the chemical reaction when iron transformed into rust.
B. Iron atoms expanded in size due to oxidation, increasing the overall mass.
C. Oxygen atoms from the surrounding atmosphere reacted with the iron to form a compound.
D. The reaction was endothermic, absorbing energy that converted into measurable mass.
Answer: C
The Law of Conservation of Mass dictates that matter cannot be created or destroyed in a
chemical reaction. The increase in mass observed in the nail is due to gaseous oxygen
molecules from the air chemically combining with the solid iron atoms to form solid iron(III)
oxide. The missing mass in the initial measurement is accounted for by the atmospheric
oxygen consumed during the oxidation process.
2. A student measures the density of a pure aluminum block. The accepted density of
aluminum is 2.70 g/cm³. The student performs three trial measurements and records values
of 2.45 g/cm³, 2.46 g/cm³, and 2.45 g/cm³. Which statement correctly describes the student's
measurement results?
A. The measurements are both accurate and precise.
B. The measurements are precise but not accurate.
C. The measurements are accurate but not precise.
D. The measurements are neither accurate nor precise.
Answer: B
Precision refers to the closeness of agreement among repeated independent measurements,
while accuracy refers to the closeness of a measured value to a standard or accepted value.
The values (2.45, 2.46, 2.45) are clustered closely together, indicating high precision, but they
deviate significantly from the true accepted value of 2.70 g/cm³, indicating low accuracy.
3. Which of the following particulate diagrams best represents a pure element consisting of
diatomic molecules?
A. Single isolated spheres distributed uniformly throughout the container.
,B. Bound pairs of identical spheres distributed uniformly throughout the container.
C. Bound pairs of two distinct, differently shaded spheres throughout the container.
D. An alternating lattice arrangement of two differently sized spheres.
Answer: B
An element consists of only one type of atom. Diatomic elements (such as H2, N2, O2, F2, Cl2,
Br2, and I2) exist naturally as pairs of chemically bonded, identical atoms. Option B correctly
depicts single-element units composed of bound identical spheres, whereas Option A depicts a
monatomic element and Option C represents a binary molecular compound.
4. A sample of gas occupies 4.0 L at 2.0 atm. If the temperature remains constant, what will
be the new volume if the pressure is increased to 8.0 atm?
A. 1.0 L
B. 2.0 L
C. 8.0 L
D. 16.0 L
Answer: A
According to Boyle's Law (P1V1 = P2V2), pressure and volume are inversely proportional at
constant temperature and moles of gas. Solving for the new volume: V2 = (P1 * V1) / P2 = (2.0
atm * 4.0 L) / 8.0 atm = 1.0 L. Quadrupling the pressure results in reducing the volume to one-
fourth of its original size.
5. Which set of quantum numbers (n, l, ml, ms) is physically permissible for an electron in
an atom?
A. (2, 2, 0, +1/2)
B. (3, 1, -2, -1/2)
C. (4, 2, -1, +1/2)
D. (1, 0, 0, +1)
Answer: C
Quantum number rules dictate that n >= 1, l can range from 0 to (n - 1), ml can range from -l
to +l, and ms must be either +1/2 or -1/2. In Option C (4, 2, -1, +1/2), n=4 allows l=2 (d
orbital), l=2 allows ml=-1, and ms=+1/2 is valid. Option A is invalid because l cannot equal n.
Option B is invalid because ml cannot exceed l. Option D is invalid because ms cannot be +1.
6. A pure compound is analyzed and found to contain 40.0% carbon, 6.7% hydrogen, and
53.3% oxygen by mass. What is the empirical formula of the compound?
A. CH2O
B. C2H4O2
,C. C3H6O3
D. CHO
Answer: A
To find the empirical formula, convert mass percentages to moles assuming a 100g sample: C
= 40.0g / 12.01 g/mol = 3.33 mol; H = 6.7g / 1.008 g/mol = 6.65 mol; O = 53.3g / 16.00 g/mol
= 3.33 mol. Divide each mole quantity by the smallest value (3.33): C = 1, H = 2, O = 1. The
simplest whole-number ratio of atoms in the compound is CH2O.
7. Which of the following aqueous solutions will have the highest electrical conductivity at
room temperature?
A. 0.10 M C12H22O11 (sucrose)
B. 0.10 M CH3COOH (acetic acid)
C. 0.10 M NaCl (sodium chloride)
D. 0.10 M CaCl2 (calcium chloride)
Answer: D
Electrical conductivity in aqueous solutions depends on the concentration of mobile ions
present. Sucrose is a non-electrolyte (0 ions). Acetic acid is a weak acid that only partially
ionizes. Sodium chloride is a strong electrolyte yielding 2 moles of ions per mole of solute (Na+
and Cl-). Calcium chloride is a strong electrolyte yielding 3 moles of ions per mole of solute (1
Ca2+ and 2 Cl-), producing the highest total ion concentration (0.30 M total ions) and thus the
highest conductivity.
8. Under which conditions of temperature and pressure does a real gas deviate most
significantly from ideal behavior?
A. High temperature and low pressure
B. Low temperature and high pressure
C. High temperature and high pressure
D. Low temperature and low pressure
Answer: B
Real gases deviate from ideal behavior under conditions where intermolecular attractive
forces become significant and the volume occupied by gas molecules themselves is no longer
negligible relative to the total container volume. Low temperatures decrease molecular
kinetic energy, allowing intermolecular attractions to pull molecules together, while high
pressures force molecules into close proximity where their finite volume matters.
9. Which of the following electron configurations represents an atom in an excited state?
, A. 1s² 2s² 2p⁶ 3s²
B. 1s² 2s² 2p⁶ 3s¹ 3p¹
C. 1s² 2s² 2p⁵
D. 1s² 2s² 2p⁶ 3s² 3p⁴
Answer: B
An excited state occurs when an electron absorbs energy and transitions to a higher energy
orbital without filling the lower energy subshells according to the Aufbau principle. In
configuration B (1s² 2s² 2p⁶ 3s¹ 3p¹), one electron from the 3s subshell has been promoted to
the 3p subshell before the 3s orbital was fully occupied (which requires 3s²), indicating an
excited state.
10. What is the molecular geometry of the sulfur tetrafluoride (SF4) molecule?
A. Tetrahedral
B. Square planar
C. See-saw
D. Trigonal bipyramidal
Answer: C
Sulfur tetrafluoride (SF4) has 34 valence electrons. The central sulfur atom forms four single
bonds with fluorine atoms and retains one lone pair of electrons (AX4E notation). This results
in five electron domains around the central atom, giving a trigonal bipyramidal electron
domain geometry. Due to the equatorial placement of the single lone pair to minimize
electron repulsion, the spatial arrangement of the bonded atoms forms a see-saw molecular
geometry.
11. A student dissolves 10.0 g of potassium nitrate (KNO3) in 100.0 g of water at 25°C. The
temperature of the solution drops to 21.5°C. Which statement regarding the dissolution
process is correct?
A. The process is exothermic and ΔH is negative.
B. The process is endothermic and ΔH is positive.
C. The process is exothermic and ΔH is positive.
D. The process is endothermic and ΔH is negative.
Answer: B
A drop in temperature of the aqueous system indicates that heat energy was absorbed from
the surrounding water to break the ionic lattice interactions and solute-solute bonds. Because
the system absorbs energy from its surroundings, the process is classified as endothermic,
which is represented mathematically by a positive enthalpy change (+ΔH).
