HESI A2 Chemistry Practice Questions

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: +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: C

Rationale: The correct answer is C: 5 g. After 10 years, half of the cobalt-60 decays, leaving 10 g. After 5 more years, another half will decay, leaving 5 g. This is because the half-life of cobalt-60 is 5 years, meaning it takes 5 years for half of the initial amount to decay. Choices A, B, and D are incorrect because they do not take into account the concept of half-life and the exponential decay of radioactive substances.

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.