CHEM 219 | CHEM219 Module 1: Principles of
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. Which of the following elements is the central building block of all organic molecules due
to its ability to form four stable covalent bonds?
A. Carbon
B. Nitrogen
C. Oxygen
D. Hydrogen
Correct Answer: A
Expert Explanation: Carbon has four valence electrons which allows it to form four
covalent bonds. This unique tetravalence enables the formation of complex, diverse long
chains and rings. Nitrogen typically forms three bonds while oxygen forms two. Hydrogen
is limited to a single bond only. Carbon serves as the fundamental framework for all
biological and organic chemistry.
2. What is the hybridization of the carbon atom in a molecule of methane (CH4)?
A. sp3
B. sp2
C. sp
D. dsp2
Correct Answer: A
Expert Explanation: Methane contains a carbon atom bonded to four separate hydrogen
atoms via single sigma bonds. To accommodate four equivalent bonding pairs, the carbon
atom utilizes one s and three p orbitals. This results in four identical sp3 hybrid orbitals
arranged in space. The sp2 hybridization is associated with double bonds and sp with triple
bonds. Therefore, sp3 is the correct electronic configuration for saturated carbons like in
methane.
3. Which molecular geometry is associated with a central atom that is sp2 hybridized and has
no lone pairs?
A. Trigonal Planar
B. Tetrahedral
,C. Linear
D. Bent
Correct Answer: A
Expert Explanation: An sp2 hybridized central atom has three hybrid orbitals directed
toward the corners of an equilateral triangle. If there are no lone pairs, the substituents
occupy these three positions to minimize electron repulsion. This spatial arrangement is
specifically defined as trigonal planar geometry. Tetrahedral geometry requires sp3
hybridization with four electron domains. Linear geometry is characteristic of sp
hybridization with only two electron domains.
4. Which of the following bonds is considered the most polar based on electronegativity
differences?
A. C-H
B. C-C
C. C-N
D. O-H
Correct Answer: D
Expert Explanation: Polarity is determined by the difference in electronegativity between
the two atoms sharing a bond. Oxygen is much more electronegative than hydrogen,
creating a significant dipole moment. The C-H bond has a very small difference and is often
treated as non-polar. C-C bonds have zero difference because the atoms are identical. The
O-H bond possesses the largest difference among the provided choices in organic
chemistry.
5. In the laboratory, you observe that a substance does not dissolve in water but dissolves
readily in hexane. What can you conclude about this substance?
A. It is highly polar
B. It is non-polar
C. It is an ionic salt
D. It is a strong acid
Correct Answer: B
Expert Explanation: Solubility follows the general principle that ‘like dissolves like’
regarding polarity. Water is a highly polar solvent, while hexane is a non-polar
hydrocarbon solvent. Since the substance dissolves in hexane but not water, it must be
non-polar. Ionic salts and highly polar molecules typically dissolve well in water due to
dipole-dipole interactions. This experimental result is a classic test for identifying the
hydrophobic nature of organic compounds.
, 6. What is the bond angle typically found in a molecule with tetrahedral geometry, such as
Ethane?
A. 90 degrees
B. 120 degrees
C. 109.5 degrees
D. 180 degrees
Correct Answer: C
Expert Explanation: Tetrahedral geometry occurs when a central atom is surrounded by
four electron domains. To maximize the distance between these electron pairs, they occupy
angles of 109.5 degrees. A 120-degree angle is characteristic of trigonal planar geometry
found in sp2 systems. A 180-degree angle represents linear geometry found in sp systems.
Therefore, 109.5 is the standard bond angle for sp3 hybridized carbon atoms.
7. Which functional group is characterized by the presence of a carbon-to-carbon triple bond?
A. Alkene
B. Arene
C. Alkane
D. Alkyne
Correct Answer: D
Expert Explanation: Alkynes are hydrocarbons that contain at least one carbon-carbon
triple bond. Alkanes contain only single bonds and are considered saturated hydrocarbons.
Alkenes contain at least one carbon-carbon double bond within the molecule. Arenes
involve aromatic ring systems like benzene with alternating double bonds. The triple bond
in an alkyne consists of one sigma bond and two pi bonds.
8. Which of the following molecules has a net dipole moment of zero (is non-polar)?
A. H2O
B. NH3
C. CHCl3
D. CCl4
Correct Answer: D
Expert Explanation: Carbon tetrachloride (CCl4) has four polar C-Cl bonds arranged in a
perfectly symmetrical tetrahedral shape. Because the bond dipoles are equal and point in
opposite directions, they cancel each other out. Water and ammonia have lone pairs that
create an asymmetrical distribution of charge. Chloroform (CHCl3) is asymmetrical
Organic Chemistry with Lab - Portage Learning
Updated and Latest Questions and Correct
Answers with Rationale
1. Which of the following elements is the central building block of all organic molecules due
to its ability to form four stable covalent bonds?
A. Carbon
B. Nitrogen
C. Oxygen
D. Hydrogen
Correct Answer: A
Expert Explanation: Carbon has four valence electrons which allows it to form four
covalent bonds. This unique tetravalence enables the formation of complex, diverse long
chains and rings. Nitrogen typically forms three bonds while oxygen forms two. Hydrogen
is limited to a single bond only. Carbon serves as the fundamental framework for all
biological and organic chemistry.
2. What is the hybridization of the carbon atom in a molecule of methane (CH4)?
A. sp3
B. sp2
C. sp
D. dsp2
Correct Answer: A
Expert Explanation: Methane contains a carbon atom bonded to four separate hydrogen
atoms via single sigma bonds. To accommodate four equivalent bonding pairs, the carbon
atom utilizes one s and three p orbitals. This results in four identical sp3 hybrid orbitals
arranged in space. The sp2 hybridization is associated with double bonds and sp with triple
bonds. Therefore, sp3 is the correct electronic configuration for saturated carbons like in
methane.
3. Which molecular geometry is associated with a central atom that is sp2 hybridized and has
no lone pairs?
A. Trigonal Planar
B. Tetrahedral
,C. Linear
D. Bent
Correct Answer: A
Expert Explanation: An sp2 hybridized central atom has three hybrid orbitals directed
toward the corners of an equilateral triangle. If there are no lone pairs, the substituents
occupy these three positions to minimize electron repulsion. This spatial arrangement is
specifically defined as trigonal planar geometry. Tetrahedral geometry requires sp3
hybridization with four electron domains. Linear geometry is characteristic of sp
hybridization with only two electron domains.
4. Which of the following bonds is considered the most polar based on electronegativity
differences?
A. C-H
B. C-C
C. C-N
D. O-H
Correct Answer: D
Expert Explanation: Polarity is determined by the difference in electronegativity between
the two atoms sharing a bond. Oxygen is much more electronegative than hydrogen,
creating a significant dipole moment. The C-H bond has a very small difference and is often
treated as non-polar. C-C bonds have zero difference because the atoms are identical. The
O-H bond possesses the largest difference among the provided choices in organic
chemistry.
5. In the laboratory, you observe that a substance does not dissolve in water but dissolves
readily in hexane. What can you conclude about this substance?
A. It is highly polar
B. It is non-polar
C. It is an ionic salt
D. It is a strong acid
Correct Answer: B
Expert Explanation: Solubility follows the general principle that ‘like dissolves like’
regarding polarity. Water is a highly polar solvent, while hexane is a non-polar
hydrocarbon solvent. Since the substance dissolves in hexane but not water, it must be
non-polar. Ionic salts and highly polar molecules typically dissolve well in water due to
dipole-dipole interactions. This experimental result is a classic test for identifying the
hydrophobic nature of organic compounds.
, 6. What is the bond angle typically found in a molecule with tetrahedral geometry, such as
Ethane?
A. 90 degrees
B. 120 degrees
C. 109.5 degrees
D. 180 degrees
Correct Answer: C
Expert Explanation: Tetrahedral geometry occurs when a central atom is surrounded by
four electron domains. To maximize the distance between these electron pairs, they occupy
angles of 109.5 degrees. A 120-degree angle is characteristic of trigonal planar geometry
found in sp2 systems. A 180-degree angle represents linear geometry found in sp systems.
Therefore, 109.5 is the standard bond angle for sp3 hybridized carbon atoms.
7. Which functional group is characterized by the presence of a carbon-to-carbon triple bond?
A. Alkene
B. Arene
C. Alkane
D. Alkyne
Correct Answer: D
Expert Explanation: Alkynes are hydrocarbons that contain at least one carbon-carbon
triple bond. Alkanes contain only single bonds and are considered saturated hydrocarbons.
Alkenes contain at least one carbon-carbon double bond within the molecule. Arenes
involve aromatic ring systems like benzene with alternating double bonds. The triple bond
in an alkyne consists of one sigma bond and two pi bonds.
8. Which of the following molecules has a net dipole moment of zero (is non-polar)?
A. H2O
B. NH3
C. CHCl3
D. CCl4
Correct Answer: D
Expert Explanation: Carbon tetrachloride (CCl4) has four polar C-Cl bonds arranged in a
perfectly symmetrical tetrahedral shape. Because the bond dipoles are equal and point in
opposite directions, they cancel each other out. Water and ammonia have lone pairs that
create an asymmetrical distribution of charge. Chloroform (CHCl3) is asymmetrical
