HESI A2 Chemistry Practice Questions

Correct Answer: A

Rationale: The correct answer is A: -1. Beta particles are high-speed electrons emitted during radioactive decay. They have a negative charge due to their electron nature. Electrons are negatively charged particles. The other choices are incorrect because beta particles do not have a positive charge like choices B and C, and they do have a charge, contrary to choice D.

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: 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: B

Rationale: The correct answer is B: London dispersion force. This is the weakest intermolecular force because it occurs between temporary dipoles induced by momentary fluctuations in electron distribution. It is present in all molecules, regardless of polarity. Dipole-dipole interactions (A) are stronger as they involve permanent dipoles, hydrogen bonding (C) is stronger and specific to molecules with hydrogen directly bonded to highly electronegative atoms, and ionic bonding (D) is the strongest intermolecular force due to the electrostatic attraction between oppositely charged ions.

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.