Chemistry HESI A2 Practice Test

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: 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: Semimetals. These elements exhibit properties of both metals and nonmetals. They are also known as metalloids. B, Si, As, Te, At, Ge, and Sb are located along the staircase pattern on the periodic table, indicating their intermediate nature. They have characteristics like both metals (e.g., conductivity) and nonmetals (e.g., brittleness). Choice A (Metals) is incorrect because these elements do not exhibit all typical metal properties. Choice C (Nonmetals) is incorrect because they do not possess all nonmetal properties exclusively. Choice D (Ultrametals) is not a recognized classification in chemistry.

Correct Answer: A

Rationale: The correct answer is A (pH 3) for lemon juice. Lemon juice is acidic due to citric acid content, resulting in a low pH value. The pH scale ranges from 0-14, with 7 being neutral. Lemon juice with a pH of 3 is considered highly acidic. Choice B (pH 5) is less acidic than choice A. Choice C (pH 7) is neutral, which is not characteristic of lemon juice. Choice D (pH 9) is alkaline, opposite to the acidity of lemon juice. Lemon juice's low pH value contributes to its sour taste and preservation properties.

Correct Answer: A

Rationale: The correct answer is A because the rate of diffusion is inversely proportional to the square root of the molar mass. Therefore, if gas A has four times the molar mass of gas B, gas A would diffuse at half the rate of gas B. This is because the square root of 4 is 2, indicating that gas A would diffuse at a rate that is half of gas B. Choice B is incorrect because if gas A has four times the molar mass of gas B, it would not diffuse at twice the rate of gas B. Choice C is incorrect because gas A would not diffuse at a quarter the rate of gas B. Choice D is incorrect because gas A would not diffuse at four times the rate of gas B.