Chemistry HESI A2 Practice Test

Correct Answer: D

Rationale: The correct answer is D: Crystalline shape. Ionic compounds have a regular, repeating arrangement of ions in a crystal lattice structure due to strong electrostatic forces between oppositely charged ions. This leads to the formation of distinct geometric shapes, known as crystalline shapes. Choice A is incorrect because ionic compounds typically have high melting points due to strong ionic bonds. Choice B is incorrect as ionic compounds are good conductors when dissolved in water or in a molten state. Choice C is incorrect because ionic compounds involve transfer, not sharing, of electrons between ions.

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 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: C

Rationale: The correct answer is C: Number of neutrons. Isotopes have the same number of protons (same atomic number), but different numbers of neutrons (different mass numbers). Carbon-12 and carbon-14 both have 6 protons (atomic number for carbon), but carbon-12 has 6 neutrons while carbon-14 has 8 neutrons. Therefore, the common trait between isotopes is the number of neutrons. Explanation for why other choices are incorrect: A: Number of nuclear particles - Isotopes have different numbers of neutrons, so they do not have the same number of nuclear particles. B: Number of protons - Isotopes have the same number of protons, but different numbers of neutrons. D: Mass number - Isotopes have different mass numbers due to differing numbers of neutrons, so this is not the common trait between isotopes.

Correct Answer: B

Rationale: The correct answer is B: < 7. Acids have a pH below 7 because they release hydrogen ions when dissolved in water, making the solution acidic. A pH of 7 is neutral, not acidic. Choices A (7.5) and C (> 7) are incorrect because they indicate values above 7, which would be alkaline/basic. Choice D (7) is incorrect because it represents a neutral pH, not acidic. Thus, the correct answer is B as it accurately represents the pH range of acids.