HESI Chemistry Questions with Answers and Explanations
1.Which of the following substances allows for the fastest diffusion?
A. gas
B. solid
C. liquid
D. plasma
Explanation: Diffusion is fastest through gases. The next fastest medium for
diffusion is liquid, followed by plasma, and then solids. In chemistry, diffusion
is defined as the movement of matter by the random motions of molecules.
In a gas or a liquid, the molecules are in perpetual motion. For instance, in a
quantity of seemingly immobile air, molecules of nitrogen and oxygen are
constantly bouncing off each other. There is even some miniscule degree of
diffusion in solids, which rises in proportion to the temperature of the
substance.
2.What is the oxidation number of hydrogen in CaH2?
A. +1
B. –1
C. 0
D. +2
HESI Chemistry Questions with Answers and Explanations
,Explanation: The oxidation number of the hydrogen in CaH2 is –1. The
oxidation number is the positive or negative charge of a monoatomic ion. In
other words, the oxidation number is the numerical charge on an ion. An ion
is a charged version of an element. Oxidation number is often referred to as
oxidation state. Oxidation number is sometimes used to describe the number
of electrons that must be added or removed from an atom in order to convert
the atom to its elemental form.
3.Which of the following does not exist as a diatomic molecule?
A. boron
B. fluorine
C. oxygen
D. nitrogen
Explanation: Boron does not exist as a diatomic molecule. The other
possible answer choices, fluorine, oxygen, and nitrogen, all exist as diatomic
molecules. A diatomic molecule always appears in nature as a pair: The word
diatomic means “having two atoms.” With the exception of astatine, all of
the halogens are diatomic. Chemistry students often use the mnemonic
BrINClHOF (pronounced “brinkelhoff”) to remember all of the diatomic
elements: bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, and
fluorine. Note that not all of these diatomic elements are halogens.
4. What is another name for aqueous HI?
A. hydroiodate acid
B. hydrogen monoiodide
HESI Chemistry Questions with Answers and Explanations
, C. hydrogen iodide
D. hydriodic acid
Explanation: Hydriodic acid is another name for aqueous HI. In an aqueous
solution, the solvent is water. Hydriodic acid is a polyatomic ion, meaning
that it is composed of two or more elements. When this solution has an
increased amount of oxygen, the -ate suffix on the first word is converted to -
ic. The HESI exam will require you to know the fundamentals of naming
chemicals. This process can be quite complex, so you should carefully review
this material before your exam.
5.Which of the following could be an empirical formula?
A. C4H8
B. C2H6
C. CH
D. C3H6
Explanation: CH could be an empirical formula. An empirical formula is the
smallest expression of a chemical formula. To be empirical, a formula must
be incapable of being reduced. For this reason, answer choices A, B, and D
are incorrect, as they could all be reduced to a simpler form. Note that
empirical formulas are not the same as compounds, which do not have to be
irreducible. Two compounds can have the same empirical formula but
different molecular formulas. The molecular formula is the actual number of
atoms in the molecule.
HESI Chemistry Questions with Answers and Explanations
1.Which of the following substances allows for the fastest diffusion?
A. gas
B. solid
C. liquid
D. plasma
Explanation: Diffusion is fastest through gases. The next fastest medium for
diffusion is liquid, followed by plasma, and then solids. In chemistry, diffusion
is defined as the movement of matter by the random motions of molecules.
In a gas or a liquid, the molecules are in perpetual motion. For instance, in a
quantity of seemingly immobile air, molecules of nitrogen and oxygen are
constantly bouncing off each other. There is even some miniscule degree of
diffusion in solids, which rises in proportion to the temperature of the
substance.
2.What is the oxidation number of hydrogen in CaH2?
A. +1
B. –1
C. 0
D. +2
HESI Chemistry Questions with Answers and Explanations
,Explanation: The oxidation number of the hydrogen in CaH2 is –1. The
oxidation number is the positive or negative charge of a monoatomic ion. In
other words, the oxidation number is the numerical charge on an ion. An ion
is a charged version of an element. Oxidation number is often referred to as
oxidation state. Oxidation number is sometimes used to describe the number
of electrons that must be added or removed from an atom in order to convert
the atom to its elemental form.
3.Which of the following does not exist as a diatomic molecule?
A. boron
B. fluorine
C. oxygen
D. nitrogen
Explanation: Boron does not exist as a diatomic molecule. The other
possible answer choices, fluorine, oxygen, and nitrogen, all exist as diatomic
molecules. A diatomic molecule always appears in nature as a pair: The word
diatomic means “having two atoms.” With the exception of astatine, all of
the halogens are diatomic. Chemistry students often use the mnemonic
BrINClHOF (pronounced “brinkelhoff”) to remember all of the diatomic
elements: bromine, iodine, nitrogen, chlorine, hydrogen, oxygen, and
fluorine. Note that not all of these diatomic elements are halogens.
4. What is another name for aqueous HI?
A. hydroiodate acid
B. hydrogen monoiodide
HESI Chemistry Questions with Answers and Explanations
, C. hydrogen iodide
D. hydriodic acid
Explanation: Hydriodic acid is another name for aqueous HI. In an aqueous
solution, the solvent is water. Hydriodic acid is a polyatomic ion, meaning
that it is composed of two or more elements. When this solution has an
increased amount of oxygen, the -ate suffix on the first word is converted to -
ic. The HESI exam will require you to know the fundamentals of naming
chemicals. This process can be quite complex, so you should carefully review
this material before your exam.
5.Which of the following could be an empirical formula?
A. C4H8
B. C2H6
C. CH
D. C3H6
Explanation: CH could be an empirical formula. An empirical formula is the
smallest expression of a chemical formula. To be empirical, a formula must
be incapable of being reduced. For this reason, answer choices A, B, and D
are incorrect, as they could all be reduced to a simpler form. Note that
empirical formulas are not the same as compounds, which do not have to be
irreducible. Two compounds can have the same empirical formula but
different molecular formulas. The molecular formula is the actual number of
atoms in the molecule.
HESI Chemistry Questions with Answers and Explanations
