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HESI A2 Chemistry practice questions

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These are original practice items written to the HESI A2 blueprint (4 options, no penalty for wrong answers), not actual exam questions. Try each one before you open the answer.

Practice by topic

Topics come from the tags on our own items, so this list reflects what the bank actually covers in Chemistry rather than a generic syllabus.

Chemistry 49 in the bank Chemistry: atomic structure 44 in the bank Chemistry: bonding 44 in the bank Chemistry: periodic table 38 in the bank Chemistry: chemical reactions 33 in the bank

Chemistry sample questions

Question 1

A solution has a hydroxide ion concentration [OH-] of 1.0 x 10^-3 M. What is the pH of this solution?

  1. A 3
  2. B 14
  3. C 11
  4. D 7
Show the answer and explanation

Correct answer: C

pOH = -log(1.0 × 10⁻³) = 3. At 25°C, pH + pOH = 14, so pH = 14 - 3 = 11, a basic solution.

Why the other options are wrong:
A: 3 is the pOH; reporting it as the pH would make a basic solution look acidic.
B: 14 is the sum of pH and pOH, not the pH itself.
D: 7 is neutral, but a hydroxide concentration of 10⁻³ M is far above that of pure water.

Question 2

An atom of sodium has 11 protons and a mass number of 23. How many neutrons are in the nucleus of this atom?

  1. A 34
  2. B 11
  3. C 12
  4. D 23
Show the answer and explanation

Correct answer: C

Mass number = protons + neutrons, so neutrons = 23 - 11 = 12.

Why the other options are wrong:
A: 34 adds the protons to the mass number (23 + 11) instead of subtracting them.
B: 11 is the number of protons (the atomic number), not neutrons.
D: 23 is the mass number, the total of protons and neutrons.

Question 3

In a titration, 25.0 mL of 0.100 M HCl is titrated with 0.150 M NaOH. What volume of NaOH is required to reach the equivalence point?

  1. A 25.0 mL
  2. B 37.5 mL
  3. C 16.7 mL
  4. D 10.0 mL
Show the answer and explanation

Correct answer: C

At equivalence point, moles of acid = moles of base. Moles HCl = 0.100 M × 0.0250 L = 0.00250 mol. Volume NaOH = moles / M = 0.00250 mol / 0.150 M = 0.01667 L = 16.7 mL.

Why the other options are wrong:
A: This would be the volume if the concentrations were equal, but they are not.
B: This would be the volume if the NaOH concentration were 0.100 M (0.00250/0.100 = 0.0250 L = 25.0 mL, not 37.5). 37.5 mL would require 0.00250/0.0667 M.
D: This would be the volume if the HCl concentration were 0.0600 M or the NaOH concentration were 0.250 M.

Question 4

A laboratory technician needs to prepare 250 mL of a 2.0 M NaOH solution for a titration. How many moles of NaOH must be dissolved to make this solution?

  1. A 0.25 mol
  2. B 0.5 mol
  3. C 0.125 mol
  4. D 2.0 mol
Show the answer and explanation

Correct answer: B

Moles = molarity × liters. Convert 250 mL to 0.25 L, then 2.0 mol/L × 0.25 L = 0.5 mol of NaOH.

Why the other options are wrong:
A: 0.25 mol uses the volume in liters but leaves out the 2.0 M concentration.
C: 0.125 mol divides 0.25 L by 2.0 instead of multiplying.
D: 2.0 mol would be needed for a full liter of 2.0 M solution, not 250 mL.

Question 5

In the balanced chemical equation 2H₂ + O₂ → 2H₂O, how many hydrogen atoms appear on the product side?

  1. A 2
  2. B 1
  3. C 4
  4. D 3
Show the answer and explanation

Correct answer: C

The product side shows two water molecules (2H₂O). Each water molecule contains two hydrogen atoms, so 2 × 2 = 4 hydrogen atoms.

Why the other options are wrong:
A: 2 is the number of hydrogen atoms in a single water molecule, not in two molecules.
B: 1 is incorrect; water has two hydrogen atoms per molecule.
D: 3 does not match the stoichiometry of the balanced equation.

Question 6

In the balanced reaction 2 H2 + O2 to 2 H2O, how many moles of oxygen gas are required to completely react with 4.0 moles of hydrogen gas?

  1. A 4.0 moles
  2. B 8.0 moles
  3. C 1.0 mole
  4. D 2.0 moles
Show the answer and explanation

Correct answer: D

The equation uses 2 mol H₂ for every 1 mol O₂, so 4.0 mol H₂ × (1 mol O₂ / 2 mol H₂) = 2.0 mol O₂.

Why the other options are wrong:
A: 4.0 moles assumes a 1:1 ratio, ignoring the coefficient 2 in front of H₂.
B: 8.0 moles multiplies by 2 instead of dividing by 2.
C: 1.0 mole divides by 4 instead of 2, and it would react with only 2.0 mol H₂.

Question 7

How many milliliters of a 6.0 M H2SO4 stock solution are needed to prepare 250 mL of 1.5 M H2SO4?

  1. A 125 mL
  2. B 62.5 mL
  3. C 100 mL
  4. D 250 mL
Show the answer and explanation

Correct answer: B

Use M₁V₁ = M₂V₂: V₁ = (1.5 M × 250 mL) ÷ 6.0 M = 375 ÷ 6.0 = 62.5 mL of stock, diluted to 250 mL.

Why the other options are wrong:
A: 125 mL of 6.0 M stock diluted to 250 mL gives 3.0 M, twice the target.
C: 100 mL of stock diluted to 250 mL gives 2.4 M, still too concentrated.
D: 250 mL would be undiluted stock at 6.0 M, four times the target.

Question 8

A sample of gas occupies 4.0 L at a pressure of 2.0 atm. If the temperature remains constant and the pressure is reduced to 1.0 atm, what is the new volume of the gas?

  1. A 16.0 L
  2. B 2.0 L
  3. C 4.0 L
  4. D 8.0 L
Show the answer and explanation

Correct answer: D

Boyle's law: P₁V₁ = P₂V₂, so (2.0 atm)(4.0 L) = (1.0 atm)(V₂) and V₂ = 8.0 L. Halving the pressure doubles the volume.

Why the other options are wrong:
A: 16.0 L quadruples the volume, but halving the pressure only doubles it.
B: 2.0 L treats pressure and volume as directly proportional, but lower pressure means a larger volume.
C: 4.0 L assumes no change, but volume must change when pressure changes at constant temperature.

Question 9

An atom of the isotope carbon-14 contains 6 protons. How many neutrons are in this isotope?

  1. A 20
  2. B 6
  3. C 14
  4. D 8
Show the answer and explanation

Correct answer: D

The mass number (14) is the sum of protons and neutrons. With 6 protons, neutrons = 14 - 6 = 8.

Why the other options are wrong:
A: This would be the sum of protons and neutrons if there were 14 neutrons, but the mass number is 14, so neutrons cannot be 20.
B: This is the number of protons, not neutrons.
C: This is the mass number (protons + neutrons), not the neutron count alone.

Question 10

A water molecule has a bent shape and is polar. Which type of bond is responsible for the attraction between two separate water molecules?

  1. A Covalent bond
  2. B Ionic bond
  3. C Van der Waals force
  4. D Hydrogen bond
Show the answer and explanation

Correct answer: D

Hydrogen bonds form between the partially positive hydrogen of one water molecule and the partially negative oxygen of another water molecule. These intermolecular forces give water its high surface tension and boiling point.

Why the other options are wrong:
A: Covalent bonds are intramolecular bonds within a water molecule (O–H bonds), not between separate molecules.
B: Ionic bonds involve complete transfer of electrons between atoms, forming ions; water molecules are neutral and interact via dipole-dipole forces.
C: Van der Waals forces are weaker intermolecular forces present in all molecules, but the primary attraction between water molecules is hydrogen bonding, which is a specific, stronger dipole-dipole interaction.

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