HESI A2 Chemistry Practice Test

Correct Answer: B

Rationale: The correct answer is B: Alpha radiation. Alpha radiation emits helium ions, which are essentially helium nuclei. These particles are large and have a low penetrating ability, so they can be stopped by a piece of paper. Beta radiation (choice A) consists of fast-moving electrons and can penetrate paper but can be stopped by aluminum. Gamma radiation (choice C) is high-energy electromagnetic radiation that requires thick lead or concrete to stop. X-ray radiation (choice D) is similar to gamma radiation and also requires dense materials for shielding. Therefore, alpha radiation is the only type that fits the description of emitting helium ions and being stopped by a piece of paper.

Correct Answer: A

Rationale: The correct answer is A: A higher concentration of reactants causes more effective collisions per unit time, leading to an increased reaction rate. This is because a higher concentration means there are more reactant molecules in a given volume, increasing the chances of collisions between them. With more collisions occurring, the likelihood of effective collisions (those with sufficient energy and correct orientation) also increases, resulting in a faster reaction rate. Choices B, C, and D are incorrect: B: A lower concentration of reactants causes fewer effective collisions per unit time, leading to a decreased reaction rate - This is incorrect as lower concentration reduces the number of collisions, including effective collisions, hence decreasing the reaction rate. C: A higher concentration of reactants causes more effective collisions per unit time, leading to a decreased reaction rate - This is contradictory and illogical as a higher concentration increasing effective collisions would logically lead to an increased reaction rate. D: A higher concentration of reactants causes fewer effective collisions per unit time, leading

Correct Answer: B

Rationale: The typical oxidation state of oxygen in most compounds is -2. Oxygen is highly electronegative and tends to gain 2 electrons to achieve a stable octet configuration. This results in an oxidation state of -2 in compounds like water (H2O) and carbon dioxide (CO2). Therefore, choice B is correct. Choice A (-1) is incorrect because oxygen rarely has an oxidation state of -1 in compounds. Choice C (0) is incorrect as oxygen doesn't usually have an oxidation state of 0; it prefers to gain electrons. Choice D (-3) is incorrect as it is an uncommon oxidation state for oxygen in compounds.

Correct Answer: B

Rationale: The correct answer is B: Alpha radiation. Alpha radiation emits helium ions, which are essentially helium nuclei. These particles are large and have a low penetrating ability, so they can be stopped by a piece of paper. Beta radiation (choice A) consists of fast-moving electrons and can penetrate paper but can be stopped by aluminum. Gamma radiation (choice C) is high-energy electromagnetic radiation that requires thick lead or concrete to stop. X-ray radiation (choice D) is similar to gamma radiation and also requires dense materials for shielding. Therefore, alpha radiation is the only type that fits the description of emitting helium ions and being stopped by a piece of paper.

Correct Answer: D

Rationale: Boyle's Law states that the pressure of an ideal gas is inversely proportional to its volume when temperature and amount of gas are constant. This can be mathematically expressed as P1V1 = P2V2. As volume decreases, pressure increases and vice versa. Henry's Law relates gas solubility in liquids, Dalton's Law is about partial pressures of gases, and Brown's Law does not exist in the context of ideal gas laws. Thus, the correct answer is D (Boyle's Law).