HESI A2 Chemistry Practice Test

Correct Answer: A

Rationale: The correct answer is A because at high pressure and high temperature, real gases have increased kinetic energy and are closer together, leading to decreased intermolecular forces. This results in gas molecules behaving more like ideal gases with negligible volume and no intermolecular interactions. Choice B is incorrect because at low pressure, real gases have low kinetic energy and are far apart, causing intermolecular forces to become more significant, deviating from ideal behavior. Choice C is incorrect as the boiling point of water is a specific condition related to water and does not necessarily indicate ideal gas behavior. Choice D is incorrect because under certain conditions of high pressure and high temperature, real gases can approach ideal behavior, demonstrating that real gases can exhibit ideal behavior under specific circumstances.

Correct Answer: B

Rationale: The correct answer is B: Alloys. Alloys are mixtures of 2 or more metals, where the metals are evenly distributed at a microscopic level. This creates unique properties different from the individual metals. Solutions (A) involve a solute dissolved in a solvent, not necessarily metals. Compounds (C) are formed by chemical bonding between elements, not just a mixture. Suspensions (D) are mixtures where particles are suspended in a fluid but eventually settle out, unlike alloys which are uniform mixtures.

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: B

Rationale: Dalton's law states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the individual gases. In the given equation, Ptot = Pa + Pb, it directly represents Dalton's law where Ptot is the total pressure and Pa and Pb are component pressures. This equation shows that the total pressure is the sum of the pressures contributed by each gas in the mixture. Therefore, choice B is correct. Henry's law deals with the solubility of a gas in a liquid, not the relationship between the total and partial pressures of gases in a mixture (Choice A). Boyle's law relates pressure and volume of a gas at constant temperature, not the total and partial pressures of gases in a mixture (Choice C). Gay-Lussac's law describes the relationship between pressure and temperature of a gas at constant volume, not the total and partial pressures of gases in a mixture (Choice D).

Correct Answer: A

Rationale: The correct answer is A: Brownian motion. This phenomenon was first observed by Robert Brown in 1827. Brownian motion is the random movement of small particles suspended in a liquid, caused by the unbalanced impacts of molecules on the particle. This motion is a result of the constant and random motion of molecules in the liquid colliding with the particle, causing it to move in a zigzag pattern. Grey's kinesis (choice B) and Boyle's wave (choice C) are not valid terms associated with this concept and are therefore incorrect. Choice D (None of the above) is also incorrect as Brownian motion accurately describes the phenomenon described in the question.