ATI - HESI Chemistry Practice Test 1 — Questions and Answers
Question 1: If 0.5 moles of NaCl are dissolved in 2.0 liters of water, what is the molarity of the solution?
- 0.25 M (Correct answer)
- 0.50 M
- 1.00 M
- 2.50 M
Correct answer: 0.25 M
Molarity (M) = moles of solute ÷ liters of solution. 0.5 mol ÷ 2.0 L = 0.25 M.
Question 2: Which type of chemical bond is formed when two nonmetal atoms share electrons equally?
- Ionic bond
- Nonpolar covalent bond (Correct answer)
- Polar covalent bond
- Metallic bond
Correct answer: Nonpolar covalent bond
A nonpolar covalent bond forms when electrons are shared equally between two atoms of the same or similar electronegativity, as seen in molecules like O₂ or N₂.
Question 3: How many valence electrons does an oxygen atom (atomic number 8) have?
- 2
- 4
- 6 (Correct answer)
- 8
Correct answer: 6
Oxygen has the electron configuration 2, 6 — meaning 2 electrons in the first shell and 6 in the second (valence) shell.
Question 4: When hydrochloric acid (HCl) reacts with sodium hydroxide (NaOH) in a neutralization reaction, what are the products?
- H₂ gas and NaCl
- NaCl and H₂O (Correct answer)
- Na metal and HClO
- NaOH and Cl₂
Correct answer: NaCl and H₂O
Acid–base neutralization produces a salt and water. HCl + NaOH → NaCl (salt) + H₂O.
Question 5: Two atoms of the same element that have the same number of protons but different numbers of neutrons are called:
- Ions
- Allotropes
- Isomers
- Isotopes (Correct answer)
Correct answer: Isotopes
Isotopes are atoms of the same element (same atomic number/protons) that differ in their number of neutrons, giving them different mass numbers.
Question 6: Which statement best describes an exothermic chemical reaction?
- It absorbs heat energy from the surroundings.
- It requires a catalyst to release energy.
- It releases heat energy to the surroundings. (Correct answer)
- It only occurs at temperatures above 100 °C.
Correct answer: It releases heat energy to the surroundings.
In an exothermic reaction, the products have less energy than the reactants, so the excess energy is released as heat into the surroundings (e.g., combustion).
ATI - HESI Chemistry Practice Test 1
If 0.5 moles of NaCl are dissolved in 2.0 liters of water, what is the molarity of the solution?