HESI A2 Chemistry Practice Questions

Correct Answer: C

Rationale: The correct answer is C: metalloids. Arsenic and silicon are classified as metalloids due to their properties that are intermediate between metals and nonmetals. Metalloids have characteristics of both metals and nonmetals, such as varying conductivity, reactivity, and physical appearance. Arsenic and silicon exhibit this behavior, making them suitable examples of metalloids. Incorrect Answers: A: Metals - Arsenic and silicon do not exhibit typical metallic properties such as high electrical conductivity and luster. B: Nonmetals - While silicon can exhibit nonmetallic properties, arsenic does not fit the characteristics of a nonmetal. D: Heavy metals - Heavy metals typically refer to metals with high atomic weights, which is not the defining characteristic of arsenic and silicon.

Correct Answer: D

Rationale: The correct answer is D: Lye. Lye, also known as sodium hydroxide, forms hydroxide ions (OH-) when placed in water due to its highly alkaline nature. When lye dissociates in water, it releases hydroxide ions, which contribute to the solution's basicity. Lemon juice (A) and vinegar (C) are acidic solutions that release hydrogen ions (H+) in water. Battery acid (B) typically contains sulfuric acid, which also releases hydrogen ions in water. Therefore, only lye is the substance that forms hydroxide ions when placed in water, making it the correct answer.

Correct Answer: A

Rationale: The correct answer is A: H⁻. A hydride ion is formed when a hydrogen atom gains an extra electron, resulting in a negatively charged ion. The notation for a hydride ion is H⁻, indicating the presence of a single hydrogen atom with a negative charge. This is the only choice that accurately represents a hydride ion. Explanation of incorrect choices: B: H⁺ - This represents a hydrogen ion with a positive charge, not a hydride ion. C: OH⁻ - This represents a hydroxide ion, not a hydride ion. D: HCl - This is a compound consisting of a hydrogen atom and a chlorine atom, not a hydride ion.

Correct Answer: D

Rationale: The correct answer is D: Silicon. Silicon has an atomic mass greater than that of sodium (Na). Sodium has an atomic mass of 22.99 g/mol, whereas silicon has an atomic mass of 28.09 g/mol. Therefore, silicon's atomic mass is greater than that of sodium. Boron (A), oxygen (B), and fluorine (C) all have atomic masses lower than sodium, making them incorrect choices in this context.

Correct Answer: B

Rationale: To find moles of KBr, use formula moles = concentration (M) x volume (L). Given 4 M KBr solution in 25 mL, convert mL to L (25 mL = 0.025 L). Calculate moles = 4 mol/L x 0.025 L = 0.1 mol. Therefore, the correct answer is B (0.1 mol). Option A (0.035 mol) is too low, C (0.18 mol) is too high, and D (1.6 mol) is significantly higher due to incorrect calculations.