HESI A2 practice test

HESI A2 Chemistry Practice Test

Atoms, bonding, reactions, solutions and pH. Here are 10 HESI A2 chemistry questions, each with the answer and the reason.

Updated 2026-11-14 by the Tigertest team. Based on the HESI A2 section outlines (math, reading, vocabulary, grammar, biology, chemistry, anatomy and physiology). Physics is not included. Not affiliated with Elsevier.

1. 1.

   The isotope chlorine-37 has an atomic number of 17. How many neutrons are in the nucleus of one chlorine-37 atom?

   • A.

     20

   • B.

     17

   • C.

     37

   • D.

     54

   Answer: A.

   Neutrons equal mass number minus atomic number: 37 - 17 = 20. Seventeen is the number of protons; isotopes of chlorine differ only in their number of neutrons.

2. 2.

   Which of the following elements has the highest electronegativity on the periodic table?

   • A.

     Potassium

   • B.

     Iodine

   • C.

     Fluorine

   • D.

     Carbon

   Answer: C.

   Electronegativity increases across a period and up a group, making fluorine, at the top right, the most electronegative element. Iodine is also a halogen but sits lower in the group, so it attracts electrons less strongly.

3. 3.

   Sodium and potassium are soft, highly reactive metals that form +1 ions. To which group of the periodic table do they belong?

   • A.

     Alkali metals

   • B.

     Alkaline earth metals

   • C.

     Halogens

   • D.

     Noble gases

   Answer: A.

   Group 1 alkali metals have one valence electron, which they lose easily to form +1 ions. Alkaline earth metals are in group 2 and form +2 ions.

4. 4.

   Sodium chloride (NaCl) is held together by ionic bonds. How does an ionic bond form?

   • A.

     Two atoms share a pair of electrons

   • B.

     Atoms share electrons unequally

   • C.

     One atom transfers electrons to another

   • D.

     A hydrogen atom is attracted to a nearby oxygen atom

   Answer: C.

   In an ionic bond, sodium transfers its valence electron to chlorine, forming Na+ and Cl- ions that attract each other. Sharing electrons, equally or unequally, describes covalent bonds.

5. 5.

   What is the correct chemical name for the ionic compound with the formula CaCl2?

   • A.

     Calcium chloride

   • B.

     Calcium dichloride

   • C.

     Calcium chlorine

   • D.

     Carbon dichloride

   Answer: A.

   Ionic compounds are named metal first, then the nonmetal with an -ide ending; prefixes such as di- are used only for covalent compounds. Ca is calcium, not carbon (C).

6. 6.

   When the equation H2 + O2 -> H2O is balanced using the smallest whole numbers, what is the coefficient of H2O?

   • A.

     1

   • B.

     4

   • C.

     2

   • D.

     3

   Answer: C.

   The balanced equation is 2H2 + O2 -> 2H2O, giving 4 hydrogen atoms and 2 oxygen atoms on each side. A coefficient of 1 leaves only one oxygen atom on the product side.

7. 7.

   Solution X has a pH of 3 and solution Y has a pH of 5. How does the hydrogen ion concentration of X compare with that of Y?

   • A.

     100 times greater

   • B.

     2 times greater

   • C.

     10 times greater

   • D.

     100 times smaller

   Answer: A.

   Each pH unit is a tenfold change, and X is 2 units lower, so its H+ concentration is 10 x 10 = 100 times greater. A lower pH means more acidic, so X cannot have less H+ than Y.

8. 8.

   On a cold morning, water vapor turns directly into frost on a car windshield without becoming liquid first. Which phase change is this?

   • A.

     Sublimation

   • B.

     Condensation

   • C.

     Deposition

   • D.

     Evaporation

   Answer: C.

   Deposition is the change from gas directly to solid. Sublimation is the reverse, solid directly to gas, and condensation is gas to liquid.

9. 9.

   A nurse dissolves 0.50 mole of sodium chloride in enough water to make 250 mL of solution. What is the molarity?

   • A.

     2.0 M

   • B.

     0.50 M

   • C.

     0.125 M

   • D.

     1.0 M

   Answer: A.

   Molarity is moles of solute per liter of solution: 0.50 mol / 0.250 L = 2.0 M. Multiplying by 0.250 L instead of dividing gives 0.125 M, a common error; here sodium chloride is the solute and water is the solvent.

10. 10.

    Iodine-131, a beta emitter used in thyroid treatment, has a half-life of 8 days. If a patient receives 80 mg, how much remains after 24 days?

    • A.

      40 mg

    • B.

      20 mg

    • C.

      10 mg

    • D.

      26.7 mg

    Answer: C.

    Twenty-four days is three half-lives, so 80 mg -> 40 mg -> 20 mg -> 10 mg. The amount halves each period rather than dropping by one third each time.