HESI A2 Chemistry Questions

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.

Correct Answer: B

Rationale: The correct answer is B: Condensation. Condensation is the process in which a gas turns into a liquid by losing heat energy. During condensation, gas molecules slow down and come closer together, forming liquid droplets. Sublimation (A) is the process of a solid turning directly into a gas without passing through the liquid phase. Evaporation (C) is the process of a liquid turning into a gas. Deposition (D) is the process in which a gas transforms directly into a solid without becoming a liquid first.

Correct Answer: B

Rationale: The correct answer is B: Ionic bond. Sodium chloride is formed when sodium, a metal, transfers its electron to chlorine, a non-metal, resulting in the formation of Na+ and Cl- ions that are held together by electrostatic forces, forming an ionic bond. In an ionic bond, electrons are transferred from one atom to another, leading to the attraction between oppositely charged ions. Covalent bonds (choice A) involve sharing of electrons between atoms, which is not the case in sodium chloride. Metallic bonds (choice C) involve sharing of electrons in a sea of delocalized electrons within a metal lattice, which is not present in sodium chloride. Hydrogen bonds (choice D) are weaker intermolecular forces that occur between molecules containing hydrogen bonded to highly electronegative atoms like oxygen or nitrogen, which is not relevant to the bonding in sodium chloride.

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: B

Rationale: The correct answer is B: Fluorine. Fluorine is the most electronegative element because it has the highest electronegativity value on the periodic table. Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. Fluorine has the highest electronegativity value of 3.98, indicating its strong ability to attract electrons. Oxygen (A) is also highly electronegative but has a lower value than fluorine. Nitrogen (C) is less electronegative than oxygen. Sodium (D) is a metal and has low electronegativity compared to the nonmetals listed.