Chemistry HESI A2 Practice Test

Correct Answer: B

Rationale: The correct answer is B: Absolute zero. Kelvin is based on the concept of absolute zero, which is the coldest possible temperature where particles have minimal kinetic energy. This forms the foundation for the Kelvin temperature scale. A: Freezing point is incorrect because Kelvin is not specifically based on the freezing point of any substance. C: Boiling point is incorrect as Kelvin is not directly linked to the boiling point of any substance. D: Evaporation point is incorrect because Kelvin does not relate to the point at which a substance undergoes evaporation.

Correct Answer: B

Rationale: The molar mass of a substance is the mass of one mole of that substance. The molar mass of water (H2O) can be calculated by adding the atomic masses of its components (2 hydrogen atoms + 1 oxygen atom). Hydrogen's atomic mass is approximately 1 g/mol, and oxygen's atomic mass is approximately 16 g/mol. Therefore, the molar mass of water is 2(1) + 16 = 18 g/mol. This makes choice B (18 g/mol) the correct answer. Choices A, C, and D are incorrect because they do not reflect the accurate molar mass calculation of water based on the atomic masses of its components.

Correct Answer: B

Rationale: The correct answer is B: Anion. When an atom gains one or more electrons, it becomes negatively charged, forming an anion. This process is known as gaining electron(s) to achieve a stable electron configuration. A cation (A) is formed when an atom loses electron(s) and becomes positively charged. Isotope (C) refers to atoms of the same element with different numbers of neutrons. Electron (D) is a fundamental subatomic particle, not a term for an atom gaining electrons.

Correct Answer: B

Rationale: The correct answer is B: -1. In HCl, hydrogen is always assigned an oxidation state of +1. Since the overall charge of HCl is 0, the oxidation state of chlorine must be -1 to balance the charge. Chlorine is more electronegative than hydrogen and tends to gain an electron in this compound. Therefore, the oxidation state of the chlorine atom in HCl is -1. Choice A: +1 - Hydrogen is always assigned an oxidation state of +1 in compounds. Choice C: +2 - Chlorine does not have an oxidation state of +2 in HCl. Choice D: -2 - Chlorine's oxidation state is not -2 in HCl.

Correct Answer: C

Rationale: The correct answer is C: Fluorine. Fluorine is not an allotrope of carbon because allotropes are different forms of the same element. Fluorine is a different element altogether. Diamond, graphite, and buckminsterfullerene are all allotropes of carbon, each with unique molecular structures and properties. Diamond has a tetrahedral structure, graphite has layers of hexagonal rings, and buckminsterfullerene has a spherical shape. Fluorine, on the other hand, is a diatomic molecule consisting of two atoms of fluorine bonded together. Therefore, C is the correct answer as it does not belong to the category of carbon allotropes.