HESI A2 Chemistry Practice Questions: 25 Problems With Answers
Chemistry can feel difficult when formulas and unfamiliar terminology appear together. A useful preparation strategy is to learn the basic ideas first: the structure of atoms, the periodic table, chemical bonding, mixtures, solutions, and simple calculations. The following original Naxles questions provide a starting point for revision. Check your program's requirements because not every nursing entrance exam includes the same science sections.
Practice questions
1. What is the smallest unit of an element that retains the chemical identity of that element?
- A. Atom
- B. Tissue
- C. Organ
- D. Compound
Answer: A. Atom. An atom is the basic unit of a chemical element.
2. Which subatomic particle has a negative electrical charge?
- A. Proton
- B. Neutron
- C. Electron
- D. Nucleus
Answer: C. Electron. Electrons carry negative charge; protons are positive and neutrons are neutral.
3. The atomic number of an element equals its number of:
- A. Protons
- B. Neutrons only
- C. Electron shells
- D. Isotopes
Answer: A. Protons. The number of protons identifies the element.
4. Which bond involves the sharing of electron pairs between atoms?
- A. Covalent bond
- B. Ionic bond
- C. Gravitational force
- D. Magnetic field
Answer: A. Covalent bond. Covalent bonding involves shared electron pairs.
5. An ionic bond is primarily associated with:
- A. Electrostatic attraction between oppositely charged ions
- B. Sharing every electron equally
- C. The disappearance of all charges
- D. The formation of a nucleus
Answer: A. Ionic compounds form through attraction between positive and negative ions.
6. What is the chemical formula for water?
- A. CO₂
- B. H₂O
- C. NaCl
- D. O₂
Answer: B. H₂O. Each water molecule contains two hydrogen atoms and one oxygen atom.
7. What is the pH of a neutral aqueous solution at approximately 25°C?
- A. 1
- B. 5
- C. 7
- D. 14
Answer: C. 7. At approximately 25°C, neutral water has a pH near 7.
8. A solution with a pH of 3 is best described as:
- A. Acidic
- B. Neutral
- C. Basic
- D. Without hydrogen ions
Answer: A. Acidic. Values below 7 are acidic under the usual introductory chemistry model.
9. Which substance is a common example of an acid?
- A. Hydrochloric acid
- B. Sodium chloride
- C. Pure oxygen
- D. Helium
Answer: A. Hydrochloric acid. Hydrochloric acid releases hydrogen ions in aqueous solution.
10. What is a solute?
- A. The substance dissolved in a solvent
- B. The container holding a solution
- C. The temperature of a liquid
- D. A type of atom nucleus
Answer: A. In a solution of salt water, salt is the solute and water is the solvent.
11. Which is an example of a mixture?
- A. Air
- B. A single pure gold element
- C. A single oxygen atom
- D. One isolated proton
Answer: A. Air. Air contains several gases mixed together.
Answer: A. Air. Air contains several gases mixed together.
12. What is the approximate mass number of an atom?
- A. Protons plus neutrons
- B. Protons minus electrons
- C. Electrons only
- D. Neutrons divided by protons
Answer: A. The mass number is the total number of protons and neutrons in the nucleus.
13. What does a catalyst do?
- A. Speeds up a reaction by providing a pathway with lower activation energy
- B. Always gets used up completely
- C. Increases the mass of every reactant
- D. Prevents every chemical reaction
Answer: A. A catalyst increases reaction rate without being consumed overall.
14. Which state of matter has a definite volume but takes the shape of its container?
- A. Solid
- B. Liquid
- C. Gas
- D. Plasma only
Answer: B. Liquid. Liquids have a relatively definite volume but flow to match their container.
15. What is the symbol for sodium?
- A. S
- B. So
- C. Na
- D. N
Answer: C. Na. Sodium's symbol comes from its Latin name, natrium.
16. Which formula represents carbon dioxide?
- A. CO
- B. CO₂
- C. C₂O
- D. CaO
Answer: B. CO₂. Each molecule contains one carbon atom and two oxygen atoms.
17. How many atoms are represented in one molecule of H₂O?
- A. 1
- B. 2
- C. 3
- D. 4
Answer: C. 3. The molecule contains two hydrogen atoms and one oxygen atom.
18. What happens to the total mass in a closed system during an ordinary chemical reaction?
- A. It is conserved.
- B. It always doubles.
- C. It always becomes zero.
- D. It depends only on the color change.
Answer: A. The law of conservation of mass states that total mass remains constant in a closed system during a chemical reaction.
Answer: A. The law of conservation of mass states that total mass remains constant in a closed system during a chemical reaction.
- A. 10 g/mol
- B. 18 g/mol
- C. 28 g/mol
- D. 44 g/mol
Answer: B. 18 g/mol. Two hydrogen atoms contribute about 2 g/mol and one oxygen atom about 16 g/mol.
20. What is the concentration in g/L of a solution containing 10 g of solute in 2 L of solution?
- A. 2 g/L
- B. 5 g/L
- C. 10 g/L
- D. 20 g/L
Answer: B. 5 g/L. Concentration =10 g÷2 L=5 g/L
21. What is an isotope?
- A. Atoms of the same element with different numbers of neutrons
- B. Atoms with different numbers of protons but the same identity
- C. A mixture of liquids
- D. A type of chemical bond
Answer: A. Isotopes have the same proton number but different neutron numbers.
22. Which process changes a liquid into a gas at its surface?
- A. Evaporation
- B. Freezing
- C. Condensation
- D. Deposition
Answer: A. Evaporation. Surface molecules gain enough energy to enter the gas phase.
23. What is the main difference between an element and a compound?
- A. An element contains one type of atom; a compound contains chemically combined elements.
- B. A compound always contains only one atom.
- C. Elements are always liquids.
- D. Compounds cannot be separated by chemical processes.
Answer: A. Compounds contain two or more elements chemically combined in defined proportions.
24. Which statement about acids and bases is generally correct?
- A. Acids and bases can react in a neutralization reaction.
- B. Acids never react with bases.
- C. Every solution has exactly the same pH.
- D. Bases cannot exist in water.
Answer: A. Acid-base neutralization commonly produces water and a salt, depending on the reactants.
25. What is the coefficient of oxygen when the equation 2H 2 +O 2 →2H 2 O is balanced?
- A. 1
- B. 2
- C. 3
- D. 4
Answer: A. 1. One oxygen molecule reacts with two hydrogen molecules to produce two water molecules.
Chemistry study strategy
Create a one-page reference sheet for common symbols, formulas, and definitions. Practice calculations by writing down the known values, selecting the appropriate relationship, and checking whether your answer has sensible units.
