200+ QUESTIONS & ANSWERS WITH
RATIONALES
, WGU D425 INTRODUCTION TO CHEMISTRY: MIDTERM & FINAL EXAM PRACTICE BUNDLE
(QUESTIONS 16-100)
Section 1: Foundational Concepts, Matter, and Measurement
Question 1:
Which of the following is a compound?
A) Air
B) Sodium
C) Water
D) Gold
Answer: C) Water
Rationale: A compound is a substance with a fixed composition of two or more elements that
are chemically bonded in a fixed ratio. Water (H₂O) is composed of hydrogen and oxygen atoms
chemically bonded. Air is a mixture of gases, while sodium (Na) and gold (Au) are elements in
their standard states .
Question 2:
An unknown substance melts at 801°C and conducts electricity when molten but not in its solid
state. This substance is most likely a(n):
A) Ionic compound
B) Metallic element
C) Covalent network solid
D) Molecular compound
Answer: A) Ionic compound
Rationale: Ionic compounds, such as NaCl, typically have high melting points. They conduct
electricity when molten or dissolved in water because the ions are free to move and carry
charge. In a solid state, the ions are locked in a crystal lattice and cannot conduct electricity.
,Metals conduct electricity in their solid state, while molecular compounds generally have low
melting points .
Question 3:
A student measures the mass of a liquid as 25.30 g and its volume as 30.0 mL. Using the correct
number of significant figures, what is its density?
A) 0.843 g/mL
B) 0.84 g/mL
C) 0.8433 g/mL
D) 0.8 g/mL
Answer: A) 0.843 g/mL
Rationale: Density is calculated by dividing mass by
volume: 25.30 g/30.0 mL=0.84333 g/mL25.30 g/30.0 mL=0.84333 g/mL. The volume
measurement (30.0 mL) has three significant figures, which is the least number of significant
figures in the calculation. Therefore, the answer must be rounded to three significant figures,
giving 0.843 g/mL .
Question 4:
An irregularly shaped metal object with a mass of 80.4 g is placed in a graduated cylinder
containing 500.5 mL of water. The water level rises to 512.5 mL. What is the density of the
metal?
A) 0.149 g/mL
B) 15.6 g/mL
C) 6.70 g/mL
D) 6.7 g/mL
Answer: C) 6.70 g/mL
Rationale: The volume of the metal is found by water
displacement: 512.5 mL−500.5 mL=12.0 mL512.5 mL−500.5 mL=12.0 mL. The density is
, then Density=Mass/Volume=80.4 g/12.0 mL=6.70 g/mLDensity=Mass/Volume=80.4 g/12.0 mL=
6.70 g/mL. The answer is limited to three significant figures .
Section 2: Atomic Structure and Chemical Bonding
Question 5:
How many protons, neutrons, and electrons are in the 40Ca2+40Ca2+ ion?
A) 20 p, 20 n, 18 e⁻
B) 20 p, 20 n, 20 e⁻
C) 20 p, 40 n, 18 e⁻
D) 40 p, 20 n, 20 e⁻
Answer: A) 20 p, 20 n, 18 e⁻
Rationale: The atomic number (Z) of calcium is 20, which means a neutral atom has 20 protons
and 20 electrons. The mass number (A) is 40, so the number of neutrons
is A−Z=40−20=20A−Z=40−20=20. The 2+ charge indicates the atom has lost 2 electrons,
leaving 20−2=1820−2=18 electrons .
Question 6:
What type of chemical bond forms between sodium (Na) and chlorine (Cl)?
A) Covalent
B) Metallic
C) Ionic
D) Hydrogen
Answer: C) Ionic
Rationale: The bond between sodium and chlorine is ionic. Sodium is a metal and chlorine is a
non-metal. The large difference in their electronegativities causes sodium to transfer an
electron to chlorine, forming Na⁺ and Cl⁻ ions. The electrostatic attraction between these
oppositely charged ions forms an ionic bond .
RATIONALES
, WGU D425 INTRODUCTION TO CHEMISTRY: MIDTERM & FINAL EXAM PRACTICE BUNDLE
(QUESTIONS 16-100)
Section 1: Foundational Concepts, Matter, and Measurement
Question 1:
Which of the following is a compound?
A) Air
B) Sodium
C) Water
D) Gold
Answer: C) Water
Rationale: A compound is a substance with a fixed composition of two or more elements that
are chemically bonded in a fixed ratio. Water (H₂O) is composed of hydrogen and oxygen atoms
chemically bonded. Air is a mixture of gases, while sodium (Na) and gold (Au) are elements in
their standard states .
Question 2:
An unknown substance melts at 801°C and conducts electricity when molten but not in its solid
state. This substance is most likely a(n):
A) Ionic compound
B) Metallic element
C) Covalent network solid
D) Molecular compound
Answer: A) Ionic compound
Rationale: Ionic compounds, such as NaCl, typically have high melting points. They conduct
electricity when molten or dissolved in water because the ions are free to move and carry
charge. In a solid state, the ions are locked in a crystal lattice and cannot conduct electricity.
,Metals conduct electricity in their solid state, while molecular compounds generally have low
melting points .
Question 3:
A student measures the mass of a liquid as 25.30 g and its volume as 30.0 mL. Using the correct
number of significant figures, what is its density?
A) 0.843 g/mL
B) 0.84 g/mL
C) 0.8433 g/mL
D) 0.8 g/mL
Answer: A) 0.843 g/mL
Rationale: Density is calculated by dividing mass by
volume: 25.30 g/30.0 mL=0.84333 g/mL25.30 g/30.0 mL=0.84333 g/mL. The volume
measurement (30.0 mL) has three significant figures, which is the least number of significant
figures in the calculation. Therefore, the answer must be rounded to three significant figures,
giving 0.843 g/mL .
Question 4:
An irregularly shaped metal object with a mass of 80.4 g is placed in a graduated cylinder
containing 500.5 mL of water. The water level rises to 512.5 mL. What is the density of the
metal?
A) 0.149 g/mL
B) 15.6 g/mL
C) 6.70 g/mL
D) 6.7 g/mL
Answer: C) 6.70 g/mL
Rationale: The volume of the metal is found by water
displacement: 512.5 mL−500.5 mL=12.0 mL512.5 mL−500.5 mL=12.0 mL. The density is
, then Density=Mass/Volume=80.4 g/12.0 mL=6.70 g/mLDensity=Mass/Volume=80.4 g/12.0 mL=
6.70 g/mL. The answer is limited to three significant figures .
Section 2: Atomic Structure and Chemical Bonding
Question 5:
How many protons, neutrons, and electrons are in the 40Ca2+40Ca2+ ion?
A) 20 p, 20 n, 18 e⁻
B) 20 p, 20 n, 20 e⁻
C) 20 p, 40 n, 18 e⁻
D) 40 p, 20 n, 20 e⁻
Answer: A) 20 p, 20 n, 18 e⁻
Rationale: The atomic number (Z) of calcium is 20, which means a neutral atom has 20 protons
and 20 electrons. The mass number (A) is 40, so the number of neutrons
is A−Z=40−20=20A−Z=40−20=20. The 2+ charge indicates the atom has lost 2 electrons,
leaving 20−2=1820−2=18 electrons .
Question 6:
What type of chemical bond forms between sodium (Na) and chlorine (Cl)?
A) Covalent
B) Metallic
C) Ionic
D) Hydrogen
Answer: C) Ionic
Rationale: The bond between sodium and chlorine is ionic. Sodium is a metal and chlorine is a
non-metal. The large difference in their electronegativities causes sodium to transfer an
electron to chlorine, forming Na⁺ and Cl⁻ ions. The electrostatic attraction between these
oppositely charged ions forms an ionic bond .
