HESI A2 Chemistry Practice Questions

Correct Answer: B

Rationale: The correct answer is B (H₂SO₄) because it is a strong acid that completely dissociates into ions in water, leading to a high concentration of H⁺ ions. This is indicated by its ability to donate multiple protons. Choice A (CH₃COOH) is a weak acid that only partially dissociates. Choice C (NH₃) is a weak base that accepts protons rather than donating them. Choice D (KOH) is a strong base that dissociates completely in water but is not an acid.

Correct Answer: C

Rationale: Rationale for the correct answer (C): A saturated solution has the maximum concentration of solute dissolved in the solvent. At this point, the rate of dissolution equals the rate of crystallization, achieving a dynamic equilibrium. As a result, adding more solute will not increase its concentration further. Choice A is incorrect because a saturated solution has exactly the right amount of solute dissolved. Choice B is incorrect because a saturated solution is at its maximum solubility. Choice D is incorrect because a precipitate would indicate an unsaturated solution.

Correct Answer: B

Rationale: The correct answer is B: Pyridine (C5H5N) because it is not a hydrocarbon. Hydrocarbons are compounds composed of only carbon and hydrogen atoms. Pyridine contains nitrogen in addition to carbon and hydrogen, making it a heterocyclic compound. Methane, ethane, and propane are all hydrocarbons as they only contain carbon and hydrogen atoms. Pyridine is not a hydrocarbon as it contains nitrogen in its chemical structure, making it the only non-hydrocarbon option among the choices.

Correct Answer: A

Rationale: The correct answer is A: +1. In KCl, potassium is a group 1 element, which always has an oxidation state of +1 in its compounds. Chlorine, a group 17 element, has an oxidation state of -1 in most compounds. Therefore, the oxidation state of potassium in KCl must be +1 to balance the -1 oxidation state of chlorine. Choices B, C, and D are incorrect because they do not align with the known oxidation states of potassium and chlorine in this compound.

Correct Answer: A

Rationale: The net charge of an ionic compound is 0 because it consists of positively charged cations and negatively charged anions that balance each other out. Positively charged ions are formed by losing electrons, while negatively charged ions are formed by gaining electrons. In an ionic compound, the total positive charge from cations equals the total negative charge from anions, resulting in a net charge of 0. Other choices are incorrect: B: -1 - Not all ionic compounds have a net charge of -1. C: +1 - Not all ionic compounds have a net charge of +1. D: Variable - While some ionic compounds may have variable charges for transition metals, the net charge of the compound as a whole remains 0 due to the equal number of positive and negative charges.