HESI A2 Chemistry Practice Test

Correct Answer: D

Rationale: Rationale: 1. Statement A is correct as solubility is indeed defined by the concentration in a saturated solution. 2. Statement B is correct as substances with very low solubilities are typically considered insoluble. 3. Statement C is correct as a saturated solution cannot dissolve any more solute. 4. Therefore, all statements (A, B, and C) are correct, making option D the correct choice. Other options are incorrect as they do not accurately define solubility or saturated solutions.

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.

Correct Answer: A

Rationale: Correct Answer: A Rationale: 1. pH is a measure of hydrogen ion concentration in a solution. 2. The formula for pH is pH = - log[H+]. 3. This formula indicates an inverse logarithmic relationship between pH and H+ concentration. 4. The effective concentration of hydrogen ions directly influences pH. 5. The molarity of H+ ions is crucial in determining the pH value of a solution. Summary: Choice A is correct as it accurately describes the relationship between pH and hydrogen ion concentration, supported by the logarithmic formula. Choices B, C, and D are incorrect as they misinterpret the role of pH and its relationship to hydrogen ions in a solution.

Correct Answer: D

Rationale: The correct answer is D, the law of constant composition. This law states that a compound always contains the same elements in the same proportion by mass. In the case of water, the ratio of hydrogen to oxygen by mass is always 1:8, regardless of the source or quantity of water. This is a key principle in chemistry and helps identify and characterize different compounds. A: The law of multiple proportions deals with the ratios of different elements that can combine to form different compounds, not the same compound. B: The law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. C: The law of conservation of energy states that energy cannot be created or destroyed, but this is not directly related to the composition of compounds.

Correct Answer: B

Rationale: The correct answer is B because an amphoteric substance can both donate and accept protons, making it capable of acting as both an acid and a base depending on the reaction it is involved in. Choices A, C, and D are incorrect because they present limited definitions that do not encompass the dual nature of amphoteric substances. A and C are too restrictive, focusing on only one aspect of the substance's behavior, while D is entirely inaccurate as amphoteric substances can indeed act as both a base and an acid.