HESI A2 Chemistry Practice Questions

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: 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: D

Rationale: The correct answer is D: column. Elements in the same column of the periodic table, also known as groups, have similar properties due to the same number of valence electrons. This similarity is a result of the elements' electronic configuration, leading to comparable chemical behavior. In contrast, rows (choice A) represent periods, indicating elements with increasing atomic numbers but not necessarily similar properties. Principal energy levels (choice B) are related to the energy levels of electrons in an atom, not the grouping of elements. Choice C, period, refers to elements arranged horizontally on the periodic table, which do not share the same properties as elements in the same column.

Correct Answer: C

Rationale: To calculate the molar mass of hydrogen iodide (HI), we add the atomic masses of hydrogen (1 g/mol) and iodine (127 g/mol). Therefore, the molar mass of HI is 1 + 127 = 128 g/mol. Rounding to the nearest whole number, the mass of one mole of hydrogen iodide is 128 g/mol, making choice C (87 g/mol) incorrect. Choices A (2 g/mol) and B (58 g/mol) are also incorrect as they do not reflect the correct molar mass of hydrogen iodide.