HESI A2 Chemistry Practice Test

Correct Answer: B

Rationale: The correct answer is B: 20. Essential amino acids are those that the human body cannot produce on its own and must be obtained from diet. Humans require 9 essential amino acids. Since the total number of amino acids required for human life is 20, including the 9 essential ones, the correct answer is 20. Choices A, C, and D are incorrect because they do not align with the established fact that humans need 20 amino acids for survival, with 9 being essential.

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: C

Rationale: The statement that the volume of a gas is directly proportional to its absolute temperature at constant pressure aligns with Charles' Law. This law states that for a fixed amount of gas at a constant pressure, the volume of the gas is directly proportional to its absolute temperature. As the temperature increases, the volume of the gas also increases proportionally. This relationship is depicted by the equation V1/T1 = V2/T2. The other choices are incorrect because the Combined Gas Law involves pressure, volume, and temperature changes simultaneously; Boyle's Law describes the inverse relationship between pressure and volume at constant temperature, and the Ideal Gas Law is a combination of Boyle's, Charles', and Avogadro's Laws.

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: 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.