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HESI A2 Chemistry exam V1 and V2 Newest Exam
Preparation With Complete Questions And Correct
Answers With Rationales Already Graded A+Brand
New Version!!
Question 1
If a hydrogen atom is in a compound (except in metal hydrides), what is
its oxidation number?
A) 0
B) +1
C) -1
D) +2
Answer: B) +1
Explanation: In most compounds, hydrogen is assigned an oxidation
number of +1 when bonded to nonmetals. This is because hydrogen is
less electronegative than nonmetals such as oxygen, nitrogen, or
carbon, so it loses its single electron to achieve a +1 oxidation state. The
exception occurs in metal hydrides (e.g., NaH, CaH₂), where hydrogen
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has an oxidation number of -1 because metals are less electronegative
than hydrogen.
Question 2
What is the oxidation number of oxygen in most of its compounds, such
as H₂O?
A) +2
B) 0
C) -2
D) +1
Answer: C) -2
Explanation: Oxygen almost always has an oxidation number of -2 in its
compounds. This is because oxygen is highly electronegative and readily
gains two electrons to achieve a stable octet configuration. The primary
exceptions are peroxides (e.g., H₂O₂), where oxygen has an oxidation
number of -1, and compounds with fluorine, where oxygen can have a
positive oxidation number because fluorine is more electronegative.
Question 3
What is the oxidation number of an element in its elemental
(uncombined) form?
A) +1
B) 0
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C) -1
D) Depends on the element
Answer: B) 0
Explanation: By definition, any element in its standard state—whether
monatomic (e.g., He, Ne) or diatomic (e.g., O₂, N₂, Cl₂)—has an
oxidation number of zero. This is because the atoms are not bonded to
atoms of different elements, so there is no transfer or unequal sharing
of electrons that would create a net charge.
Question 4
What is the oxidation number of a simple monatomic ion?
A) Always +1
B) Always -1
C) Equal to the charge of the ion
D) Always 0
Answer: C) Equal to the charge of the ion
Explanation: For a monatomic ion, the oxidation number is identical to
the ionic charge. For example, Na⁺ has an oxidation number of +1, Cl⁻
has -1, Mg²⁺ has +2, and O²⁻ has -2. This reflects the actual electron loss
or gain that created the ion.
Question 5
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What is the oxidation state of sulfur in sulfuric acid (H₂SO₄)?
A) +4
B) 0
C) -2
D) +6
Answer: D) +6
Explanation: To determine the oxidation state of sulfur, we use the
known oxidation numbers of hydrogen (+1) and oxygen (-2). The
compound is neutral, so the sum of all oxidation numbers must equal
zero. Let x be the oxidation number of sulfur: 2(+1) + x + 4(-2) = 0, which
gives 2 + x - 8 = 0, so x = +6. Thus sulfur is in the +6 oxidation state in
sulfuric acid.
Question 6
Carbon-14 has a mass number of 14 and an atomic number of 6. How
many neutrons does it contain?
A) 6
B) 8
C) 14
D) 20
Answer: B) 8
HESI A2 Chemistry exam V1 and V2 Newest Exam
Preparation With Complete Questions And Correct
Answers With Rationales Already Graded A+Brand
New Version!!
Question 1
If a hydrogen atom is in a compound (except in metal hydrides), what is
its oxidation number?
A) 0
B) +1
C) -1
D) +2
Answer: B) +1
Explanation: In most compounds, hydrogen is assigned an oxidation
number of +1 when bonded to nonmetals. This is because hydrogen is
less electronegative than nonmetals such as oxygen, nitrogen, or
carbon, so it loses its single electron to achieve a +1 oxidation state. The
exception occurs in metal hydrides (e.g., NaH, CaH₂), where hydrogen
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has an oxidation number of -1 because metals are less electronegative
than hydrogen.
Question 2
What is the oxidation number of oxygen in most of its compounds, such
as H₂O?
A) +2
B) 0
C) -2
D) +1
Answer: C) -2
Explanation: Oxygen almost always has an oxidation number of -2 in its
compounds. This is because oxygen is highly electronegative and readily
gains two electrons to achieve a stable octet configuration. The primary
exceptions are peroxides (e.g., H₂O₂), where oxygen has an oxidation
number of -1, and compounds with fluorine, where oxygen can have a
positive oxidation number because fluorine is more electronegative.
Question 3
What is the oxidation number of an element in its elemental
(uncombined) form?
A) +1
B) 0
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C) -1
D) Depends on the element
Answer: B) 0
Explanation: By definition, any element in its standard state—whether
monatomic (e.g., He, Ne) or diatomic (e.g., O₂, N₂, Cl₂)—has an
oxidation number of zero. This is because the atoms are not bonded to
atoms of different elements, so there is no transfer or unequal sharing
of electrons that would create a net charge.
Question 4
What is the oxidation number of a simple monatomic ion?
A) Always +1
B) Always -1
C) Equal to the charge of the ion
D) Always 0
Answer: C) Equal to the charge of the ion
Explanation: For a monatomic ion, the oxidation number is identical to
the ionic charge. For example, Na⁺ has an oxidation number of +1, Cl⁻
has -1, Mg²⁺ has +2, and O²⁻ has -2. This reflects the actual electron loss
or gain that created the ion.
Question 5
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What is the oxidation state of sulfur in sulfuric acid (H₂SO₄)?
A) +4
B) 0
C) -2
D) +6
Answer: D) +6
Explanation: To determine the oxidation state of sulfur, we use the
known oxidation numbers of hydrogen (+1) and oxygen (-2). The
compound is neutral, so the sum of all oxidation numbers must equal
zero. Let x be the oxidation number of sulfur: 2(+1) + x + 4(-2) = 0, which
gives 2 + x - 8 = 0, so x = +6. Thus sulfur is in the +6 oxidation state in
sulfuric acid.
Question 6
Carbon-14 has a mass number of 14 and an atomic number of 6. How
many neutrons does it contain?
A) 6
B) 8
C) 14
D) 20
Answer: B) 8
