HESI A2 Chemistry Practice Questions

Correct Answer: A

Rationale: The net charge of an ionic compound is 0 because it consists of positively charged cations and negatively charged anions that balance each other out. Positively charged ions are formed by losing electrons, while negatively charged ions are formed by gaining electrons. In an ionic compound, the total positive charge from cations equals the total negative charge from anions, resulting in a net charge of 0. Other choices are incorrect: B: -1 - Not all ionic compounds have a net charge of -1. C: +1 - Not all ionic compounds have a net charge of +1. D: Variable - While some ionic compounds may have variable charges for transition metals, the net charge of the compound as a whole remains 0 due to the equal number of positive and negative charges.

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.

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: 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: 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.