HESI A2 Chemistry Practice Questions

Correct Answer: A

Rationale: The correct answer is A: H⁻. A hydride ion is formed when a hydrogen atom gains an extra electron, resulting in a negatively charged ion. The notation for a hydride ion is H⁻, indicating the presence of a single hydrogen atom with a negative charge. This is the only choice that accurately represents a hydride ion. Explanation of incorrect choices: B: H⁺ - This represents a hydrogen ion with a positive charge, not a hydride ion. C: OH⁻ - This represents a hydroxide ion, not a hydride ion. D: HCl - This is a compound consisting of a hydrogen atom and a chlorine atom, not a hydride ion.

Correct Answer: D

Rationale: The molarity of a solution is defined as the number of moles of solute per liter of solution. This is because molarity is a measure of concentration and represents the ratio of moles of solute to liters of solution. In this case, the molarity of an aqueous sugar solution would be best defined as moles of sugar per liter of solution (Choice D). Explanation: A: Grams of sugar per milliliter of solution - This choice does not consider the volume of the solution and is not a standard unit for molarity. B: Moles of sugar per milliliter of solution - Molarity is defined per liter of solution, not per milliliter. C: Grams of sugar per liter of solution - Molarity is based on moles, not grams, and it is per liter of solution, not per milliliter. Summary: Choice A and B do not account for the volume of the solution, and Choice C uses the incorrect unit

Correct Answer: B

Rationale: To balance the equation Fe + Cl2 → FeCl3, we need to ensure the same number of each type of atom on both sides. Starting with Fe, we have 1 Fe on the left and 1 Fe on the right, so Fe is balanced. Next, we have 2 Cl on the left from Cl2 and 3 Cl on the right from FeCl3. To balance Cl, we need to multiply Cl2 by 3 to get 6 Cl atoms on each side. Therefore, the correct balanced equation is: 2Fe + 3Cl2 → 2FeCl3. Choice A (2Fe + 2Cl2 → 2FeCl3) is incorrect because it doesn't balance the Cl atoms properly. Choice C (3Fe + 2Cl2 → 3FeCl3) is incorrect because it doesn't balance the Fe atoms. Choice D (3Fe + 3Cl2 → 6FeCl3)

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: C

Rationale: The correct answer is C: 5 g. After 10 years, half of the cobalt-60 decays, leaving 10 g. After 5 more years, another half will decay, leaving 5 g. This is because the half-life of cobalt-60 is 5 years, meaning it takes 5 years for half of the initial amount to decay. Choices A, B, and D are incorrect because they do not take into account the concept of half-life and the exponential decay of radioactive substances.