HESI A2 Chemistry Practice Questions

Correct Answer: D

Rationale: The correct answer is D: Silicon. Silicon has an atomic mass greater than that of sodium (Na). Sodium has an atomic mass of 22.99 g/mol, whereas silicon has an atomic mass of 28.09 g/mol. Therefore, silicon's atomic mass is greater than that of sodium. Boron (A), oxygen (B), and fluorine (C) all have atomic masses lower than sodium, making them incorrect choices in this context.

Correct Answer: B

Rationale: The correct formula for calcium carbonate is CaCO₃. Calcium carbonate consists of one calcium ion (Ca²⁺) and one carbonate ion (CO₃²⁻). The calcium ion has a 2+ charge while the carbonate ion has a 2- charge, so they combine in a 1:1 ratio to balance the charges. Therefore, the correct formula is CaCO₃. Choice A (CaSO₃) is incorrect because it represents calcium sulfite, not calcium carbonate. Choice C (Ca(OH)₂) is incorrect as it represents calcium hydroxide, not calcium carbonate. Choice D (CH₃OH) is incorrect as it represents methanol, not calcium carbonate.

Correct Answer: C

Rationale: The correct answer is C: metalloids. Arsenic and silicon are classified as metalloids due to their properties that are intermediate between metals and nonmetals. Metalloids have characteristics of both metals and nonmetals, such as varying conductivity, reactivity, and physical appearance. Arsenic and silicon exhibit this behavior, making them suitable examples of metalloids. Incorrect Answers: A: Metals - Arsenic and silicon do not exhibit typical metallic properties such as high electrical conductivity and luster. B: Nonmetals - While silicon can exhibit nonmetallic properties, arsenic does not fit the characteristics of a nonmetal. D: Heavy metals - Heavy metals typically refer to metals with high atomic weights, which is not the defining characteristic of arsenic and silicon.

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: 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.