HESI A2 Chemistry Questions

Correct Answer: A

Rationale: The correct answer is A: Carbon dioxide. When an acid reacts with a carbonate, it produces carbon dioxide gas due to the chemical reaction. The acid donates hydrogen ions to the carbonate, forming carbonic acid, which then breaks down into water and carbon dioxide. Oxygen (B), hydrogen (C), and nitrogen (D) are not produced during this specific reaction and are not part of the chemical equation for the reaction between an acid and a carbonate.

Correct Answer: C

Rationale: The correct answer is C: Ammonia. Ammonia is a base because it can accept protons (H+ ions) to form ammonium ions (NH4+). It can also react with water to form ammonium hydroxide, which is a strong base. Water (choice A) is neutral, not a base. Sodium chloride (choice B) is a salt formed from the reaction of a strong acid and a strong base, not a base itself. "Salt" (choice D) is a general term for any ionic compound formed from the neutralization of an acid and a base, not specifically a base.

Correct Answer: C

Rationale: The correct answer is C: Argon. Noble gases are elements in Group 18 of the periodic table with full valence electron shells, making them stable and non-reactive. Argon is a noble gas with 8 valence electrons, fulfilling the octet rule. Hydrogen (A) is a nonmetal in Group 1, Fluorine (B) is a halogen in Group 17, and Nitrogen (D) is a nonmetal in Group 15, none of which are noble gases.

Correct Answer: B

Rationale: The correct answer is B: Production of gas. In a chemical change, new substances are formed with different properties. The production of gas is a sign of a chemical reaction due to the formation of new molecules. Choices A, C, and D are physical changes, not chemical changes. A change in shape (A) is a physical change as it does not alter the chemical composition. Melting (C) and freezing (D) are also physical changes, involving the state of matter without changing the chemical composition.

Correct Answer: A

Rationale: The correct answer is A: By lowering the pressure. When pressure is decreased, the boiling point of water also decreases, allowing it to boil at room temperature. Lower pressure reduces the amount of energy needed for water molecules to escape into the gas phase. Increasing pressure (Choice B) raises the boiling point, making it harder to boil at room temperature. Decreasing the volume (Choice C) is not directly related to the boiling point of water. Raising the boiling point (Choice D) would require increasing pressure, contradicting the premise of boiling at room temperature.