HESI A2 Chemistry Practice Questions

Correct Answer: C

Rationale: The correct formula for iron III oxide is Fe₂O₃. In this compound, iron has a +3 oxidation state and oxygen has a -2 oxidation state. By applying the criss-cross method to balance the charges, we get Fe₂O₃. Choice A (IO) is incorrect as it represents a combination of iodine and oxygen. Choice B (FeS) is incorrect as it represents iron and sulfur. Choice D (OFe₂₃) is incorrect as it has the elements in the wrong order and incorrect subscripts. Fe₂O₃ is the correct formula based on the charges and combining the elements in the correct ratios.

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: 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: The correct formula for iron III oxide is Fe₂O₃. In this compound, iron has a +3 oxidation state and oxygen has a -2 oxidation state. By applying the criss-cross method to balance the charges, we get Fe₂O₃. Choice A (IO) is incorrect as it represents a combination of iodine and oxygen. Choice B (FeS) is incorrect as it represents iron and sulfur. Choice D (OFe₂₃) is incorrect as it has the elements in the wrong order and incorrect subscripts. Fe₂O₃ is the correct formula based on the charges and combining the elements in the correct ratios.

Correct Answer: A

Rationale: The correct answer is A: 2. Helium-4 has an atomic number of 2, which represents the number of protons in its nucleus. Since the atomic number is the sum of protons and neutrons, and helium-4 has 2 protons, it must also have 2 neutrons to make the total atomic mass 4. Therefore, there are 2 neutrons in an atom of helium-4. Choice B: 3 is incorrect because it does not match the atomic number of helium-4. Choice C: 4 is incorrect as it is the total atomic mass of helium-4, not the number of neutrons. Choice D: 6 is incorrect as it does not correspond to the atomic structure of helium-4.