HESI A2 Chemistry Practice Questions

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: 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: D

Rationale: The correct answer is D: Silicon. Silicon has an atomic mass greater than that of sodium (Na). Sodium has an atomic mass of 22.99 g/mol, whereas silicon has an atomic mass of 28.09 g/mol. Therefore, silicon's atomic mass is greater than that of sodium. Boron (A), oxygen (B), and fluorine (C) all have atomic masses lower than sodium, making them incorrect choices in this context.

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: 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