HESI A2 Chemistry EXAM
HESI Chemistry Questions and Answers:
1 A mystery element has 6 protons, 6 electrons and 6 neutrons. What is its atomic number?
a. 6
b. 12
c. 18
d. Not enough information
The correct answer is A. An atom can always be identified based on the number of protons which will
always be the same for atoms of the same element. The atomic number is always equal to the number of
protons.
2. A mystery element has 13 protons, 13 electrons and 14 neutrons. What element is it?
a. Fe
b. Zr
c. Al
d. Not enough information
The correct answer is C. Atoms can always be identified with the number of protons. Since this atom
has 13 protons, the atomic number is 13, which is aluminum.
3. What are buffers?
a. Proteins
b. Solutions that resist changes in pH
c. Catalysts in a reaction
d. Inhibitors in a reaction
The correct answer is B. Buffers resist change in pH and are key to maintaining stable H+ ion
concentrations.
4. What does carbonic acid do within the human body?
a. Digests food
b. Kills viruses
c. Maintains pH of blood
The correct answer is C. Carbonic acid is a buffer that maintains the pH of human blood. Other acids
are present in the stomach in order to digest food.
Use the following chemical reaction to answer the following questions:
5. What are the reactants?
a. CH4 and O2
b. CO2 and H2O
The correct answer is A. The reactants are always on the left side of a reaction and are the atoms or
molecules present at the start of a reaction.
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,6. What are the products?
a. CH4 and O2
b. CO2 and H2O
c. Both
d. None of the above
The correct answer is B. Products are made by reactions and are always on the right side of the arrow.
7. How many hydrogen atoms are present in the reactants?
a. 2
b. 4
c. 1
d. None of the above
The correct answer is B. The subscript 4 after the H symbol indicates that there are 4 atoms of
hydrogen in CH4.
8. How many oxygen atoms are in 2 O2?
a. 2
b. 4
c. 1
d. 0
The correct answer is B. The normal sized 2 is called a coefficient. It means that there are two
molecules of whatever comes after it, in this case there are 2 molecules of O 2. O2 has 2 atoms of oxygen
and the coefficient of 2 means that there would be 4 total oxygen atoms. Coefficients are similar to
distributing in algebra. All subscript numbers involved in the compound are multiplied by the coefficient
amount.
9. How many water molecules are present in the products?
a. 2
b. 4
c. 1
d. 0
The correct answer is A. The coefficient of 2 before the water molecule indicates that there are 2 of that
molecule.
10. Which of the following is most true?
a. 2H2O has 2 hydrogen atoms total
b. 2H2O is two water molecules
c. H2O2 is two water molecules
d. None of the above
The correct answer is B. The coefficient of 2 means that there are two water molecules. In answer A,
there would be 4 hydrogen atoms since the coefficient would be multiplied by the subscript. In answer C,
there are two hydrogen atoms and two oxygen atoms.
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, 11. Which of the following is most dense?
a. A block of gold that is 12g and 4.6cm3
b. A cube that is 6g and 0.91cm3
c. A block that is 143g and 24.3cm3
The correct answer is B. In order to solve this question, one must find the density of each option and
compare them to find the highest density, which would be the densest. Answer A is 2.61 g/cm 3, solved by
12g/4.6cm3. Answer B is 6.59 g/cm3, solved by 6g/0.91cm3. Answer C is 5.88 g/cm3, solved by
143g/24.3cm3.
12. Solids will always sink in liquids.
a. True, a solid is hard and liquids are not
b. True, solids are heavier than liquids
c. False, solids have a smooth surface so they will float
d. False, it depends on the density of the solid and liquid
The correct answer is D. Substances differentiate, sink or float based on their densities. If a solid is
denser than the liquid, it will sink. If the solid is less dense than the liquid, it will float.
13. Which of the following has the most molecular interactions?
a. Solid
b. Liquid
c. Gas
d. None of the above
The correct answer is A. Solids are rigid and the atoms are tightly packed together. This means that
there are the most possible molecular interactions.
14. Which of the following has the most molecular motions?
a. Solid
b. Liquid
c. Gas
d. None of the above
The correct answer is C. Gas molecules move rapidly due to being at a high temperature. In this state of
matter, the molecules have the most motion compared to the other states.
15. Which of the following is most commonly present at very high temperatures?
a. Solid
b. Liquid
c. Gas
d. None of the above.
The correct answer is C. In order for a substance to change from a liquid to a gas, it requires a large
amount of heat to be added and is typically the state of matter that is present at very high temperatures.
16. Which of the following is false about dissociation?
a. It is reversible
b. Ions are not present
c. It involves molecules separating
The correct answer is B. Dissociation is a reaction where a compound separates into ions. It is
reversible if those ions bond together again.
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HESI Chemistry Questions and Answers:
1 A mystery element has 6 protons, 6 electrons and 6 neutrons. What is its atomic number?
a. 6
b. 12
c. 18
d. Not enough information
The correct answer is A. An atom can always be identified based on the number of protons which will
always be the same for atoms of the same element. The atomic number is always equal to the number of
protons.
2. A mystery element has 13 protons, 13 electrons and 14 neutrons. What element is it?
a. Fe
b. Zr
c. Al
d. Not enough information
The correct answer is C. Atoms can always be identified with the number of protons. Since this atom
has 13 protons, the atomic number is 13, which is aluminum.
3. What are buffers?
a. Proteins
b. Solutions that resist changes in pH
c. Catalysts in a reaction
d. Inhibitors in a reaction
The correct answer is B. Buffers resist change in pH and are key to maintaining stable H+ ion
concentrations.
4. What does carbonic acid do within the human body?
a. Digests food
b. Kills viruses
c. Maintains pH of blood
The correct answer is C. Carbonic acid is a buffer that maintains the pH of human blood. Other acids
are present in the stomach in order to digest food.
Use the following chemical reaction to answer the following questions:
5. What are the reactants?
a. CH4 and O2
b. CO2 and H2O
The correct answer is A. The reactants are always on the left side of a reaction and are the atoms or
molecules present at the start of a reaction.
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,6. What are the products?
a. CH4 and O2
b. CO2 and H2O
c. Both
d. None of the above
The correct answer is B. Products are made by reactions and are always on the right side of the arrow.
7. How many hydrogen atoms are present in the reactants?
a. 2
b. 4
c. 1
d. None of the above
The correct answer is B. The subscript 4 after the H symbol indicates that there are 4 atoms of
hydrogen in CH4.
8. How many oxygen atoms are in 2 O2?
a. 2
b. 4
c. 1
d. 0
The correct answer is B. The normal sized 2 is called a coefficient. It means that there are two
molecules of whatever comes after it, in this case there are 2 molecules of O 2. O2 has 2 atoms of oxygen
and the coefficient of 2 means that there would be 4 total oxygen atoms. Coefficients are similar to
distributing in algebra. All subscript numbers involved in the compound are multiplied by the coefficient
amount.
9. How many water molecules are present in the products?
a. 2
b. 4
c. 1
d. 0
The correct answer is A. The coefficient of 2 before the water molecule indicates that there are 2 of that
molecule.
10. Which of the following is most true?
a. 2H2O has 2 hydrogen atoms total
b. 2H2O is two water molecules
c. H2O2 is two water molecules
d. None of the above
The correct answer is B. The coefficient of 2 means that there are two water molecules. In answer A,
there would be 4 hydrogen atoms since the coefficient would be multiplied by the subscript. In answer C,
there are two hydrogen atoms and two oxygen atoms.
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, 11. Which of the following is most dense?
a. A block of gold that is 12g and 4.6cm3
b. A cube that is 6g and 0.91cm3
c. A block that is 143g and 24.3cm3
The correct answer is B. In order to solve this question, one must find the density of each option and
compare them to find the highest density, which would be the densest. Answer A is 2.61 g/cm 3, solved by
12g/4.6cm3. Answer B is 6.59 g/cm3, solved by 6g/0.91cm3. Answer C is 5.88 g/cm3, solved by
143g/24.3cm3.
12. Solids will always sink in liquids.
a. True, a solid is hard and liquids are not
b. True, solids are heavier than liquids
c. False, solids have a smooth surface so they will float
d. False, it depends on the density of the solid and liquid
The correct answer is D. Substances differentiate, sink or float based on their densities. If a solid is
denser than the liquid, it will sink. If the solid is less dense than the liquid, it will float.
13. Which of the following has the most molecular interactions?
a. Solid
b. Liquid
c. Gas
d. None of the above
The correct answer is A. Solids are rigid and the atoms are tightly packed together. This means that
there are the most possible molecular interactions.
14. Which of the following has the most molecular motions?
a. Solid
b. Liquid
c. Gas
d. None of the above
The correct answer is C. Gas molecules move rapidly due to being at a high temperature. In this state of
matter, the molecules have the most motion compared to the other states.
15. Which of the following is most commonly present at very high temperatures?
a. Solid
b. Liquid
c. Gas
d. None of the above.
The correct answer is C. In order for a substance to change from a liquid to a gas, it requires a large
amount of heat to be added and is typically the state of matter that is present at very high temperatures.
16. Which of the following is false about dissociation?
a. It is reversible
b. Ions are not present
c. It involves molecules separating
The correct answer is B. Dissociation is a reaction where a compound separates into ions. It is
reversible if those ions bond together again.
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