HESI A2 Chemistry Practice Questions

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: 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: C

Rationale: The correct formula for iron III oxide is Fe₂O₃. In this compound, iron has a +3 oxidation state and oxygen has a -2 oxidation state. By applying the criss-cross method to balance the charges, we get Fe₂O₃. Choice A (IO) is incorrect as it represents a combination of iodine and oxygen. Choice B (FeS) is incorrect as it represents iron and sulfur. Choice D (OFe₂₃) is incorrect as it has the elements in the wrong order and incorrect subscripts. Fe₂O₃ is the correct formula based on the charges and combining the elements in the correct ratios.

Correct Answer: A

Rationale: The correct answer is A: 2. Helium-4 has an atomic number of 2, which represents the number of protons in its nucleus. Since the atomic number is the sum of protons and neutrons, and helium-4 has 2 protons, it must also have 2 neutrons to make the total atomic mass 4. Therefore, there are 2 neutrons in an atom of helium-4. Choice B: 3 is incorrect because it does not match the atomic number of helium-4. Choice C: 4 is incorrect as it is the total atomic mass of helium-4, not the number of neutrons. Choice D: 6 is incorrect as it does not correspond to the atomic structure of helium-4.

Correct Answer: A

Rationale: The correct answer is A: +1. In KCl, potassium is a group 1 element, which always has an oxidation state of +1 in its compounds. Chlorine, a group 17 element, has an oxidation state of -1 in most compounds. Therefore, the oxidation state of potassium in KCl must be +1 to balance the -1 oxidation state of chlorine. Choices B, C, and D are incorrect because they do not align with the known oxidation states of potassium and chlorine in this compound.