Chemistry HESI A2 Practice Test

Correct Answer: B

Rationale: The correct answer is B: Days-long. Medical isotopes used in medicine typically have a short half-life to minimize radiation exposure to patients. A days-long half-life strikes a balance between decay rate and practical usability in medical procedures. Choice A (Seconds-long) would be too short for practical use. Choices C (Years-long) and D (Many years long) would result in prolonged radiation exposure, increasing health risks for patients.

Correct Answer: C

Rationale: The correct answer is C: Polar covalent and ionic. When an acid reacts with a base, water and a salt are produced. In water, the bonds between hydrogen and oxygen are polar covalent due to the electronegativity difference between the two atoms. In the salt formed, the bond between the cation and anion is ionic, as one atom donates electrons to the other, resulting in a strong electrostatic attraction. Choice A (Liquid and metallic) is incorrect as it does not describe the bonds formed in water and the salt. Choice B (Polar and nonpolar covalent) is incorrect because nonpolar covalent bonds do not form in this scenario. Choice D (Ionic only) is incorrect because water forms polar covalent bonds, in addition to the ionic bonds in the salt.

Correct Answer: C

Rationale: The correct answer is C: +2. An alpha particle consists of two protons and two neutrons, giving it a total charge of +2. Protons have a charge of +1 each, and neutrons have no charge. Therefore, the total charge of an alpha particle is +2. Choice A (-1) is incorrect because it is the charge of an electron. Choice B (+1) is incorrect because it represents the charge of a proton. Choice D (No charge) is incorrect because alpha particles have a positive charge due to the presence of protons.

Correct Answer: D

Rationale: The correct answer is D: Time. Time does not directly impact rates of reaction; rather, it is the duration over which a reaction occurs. Temperature affects reaction rates by increasing kinetic energy, surface area by exposing more reactant molecules, and pressure by affecting collision frequency. Time is not an influencing factor in itself, but the overall reaction rate may depend on the time taken for the reaction to complete.

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.