Chemistry HESI A2 Quizlet

Correct Answer: C

Rationale: Step-by-step rationale for why choice C (Aluminum foil) is correct: 1. Beta radiation particles are high-energy electrons or positrons. 2. Aluminum foil has a high atomic number and density, making it effective at stopping beta particles. 3. The electrons in the aluminum atoms interact with the beta particles, causing them to lose energy and stop. 4. Being thin and dense, aluminum foil can effectively block beta radiation particles. Summary of why other choices are incorrect: A. Plastic: Plastic is not dense enough to effectively stop beta particles. B. Glass: While glass is denser than plastic, it is not as effective as aluminum foil in stopping beta radiation. D. Concrete: Concrete is dense, but it is not as effective as aluminum foil in stopping beta particles due to its composition and thickness.

Correct Answer: A

Rationale: The correct answer is A: Stoichiometry. Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It involves calculating the amount of substances consumed and produced in a reaction based on balanced chemical equations. This includes determining the mole ratios, mass relationships, and volume relationships in a reaction. Choice B (Molecular chemistry) focuses on the structure and properties of molecules, not specifically on quantities in reactions. Choice C (Atomic chemistry) deals with the study of atoms and their properties, not the quantities in reactions. Choice D (Thermodynamics) concerns energy changes in chemical reactions, not the quantitative relationships between compounds. Therefore, stoichiometry is the correct choice for this question.

Correct Answer: A

Rationale: The Group IA elements, also known as alkali metals, have a +1 charge. This is because they have one valence electron, which they readily lose to achieve a stable electron configuration. This results in them forming ions with a +1 charge. Therefore, the correct answer is A. Choice B (+2) is incorrect because alkali metals do not typically form ions with a +2 charge due to their tendency to lose only one electron. Choice C (+3) is also incorrect as alkali metals do not form ions with a +3 charge. Choice D (0) is incorrect because alkali metals are known for their tendency to lose electrons to achieve a stable configuration, resulting in a positive charge.

Correct Answer: B

Rationale: The mass number represents the total number of protons and neutrons in an atom's nucleus. The atomic number represents the number of protons. By subtracting the atomic number from the mass number, we are left with the number of neutrons. Therefore, the correct answer is B: Number of neutrons. Summary: A: Number of electrons - Incorrect, as the mass number minus the atomic number does not give the number of electrons. C: Number of protons - Incorrect, as the atomic number itself represents the number of protons. D: Number of isotopes - Incorrect, as isotopes refer to atoms of the same element with different numbers of neutrons, not the result of mass number minus atomic number.

Correct Answer: B

Rationale: The correct answer is B: Gas. Gases change in volume with changes in temperature and pressure according to the ideal gas law (PV = nRT). When temperature or pressure increases, gas molecules move faster and occupy more space, leading to an increase in volume. Liquids (choice A) have relatively fixed volumes, solids (choice C) have definite shapes and volumes, and plasmas (choice D) are ionized gases with unique properties but still do not change volume based on temperature and pressure changes.