HESI A2 Chemistry Questions

Correct Answer: C

Rationale: The correct answer is C: Ammonia. Ammonia is a base because it can accept protons (H+ ions) to form ammonium ions (NH4+). It can also react with water to form ammonium hydroxide, which is a strong base. Water (choice A) is neutral, not a base. Sodium chloride (choice B) is a salt formed from the reaction of a strong acid and a strong base, not a base itself. "Salt" (choice D) is a general term for any ionic compound formed from the neutralization of an acid and a base, not specifically a base.

Correct Answer: A

Rationale: The correct answer is A: Covalent bond. In a covalent bond, two atoms share electrons to complete their outer electron shells and achieve stability. This sharing results in a strong bond between the atoms. Ionic bonds involve the transfer of electrons, metallic bonds involve a "sea" of shared electrons in a metal lattice, and hydrogen bonds are weaker interactions between a hydrogen atom and an electronegative atom. Covalent bonds are the only option where electrons are shared between atoms to form a stable bond.

Correct Answer: B

Rationale: The correct answer is B: periods. Periods are the horizontal rows in the periodic table that represent the energy levels of the elements. They indicate the number of electron shells present in an element. Groups (A) are the vertical columns, representing elements with similar chemical properties. Families (C) are also vertical columns that share similar characteristics. Sets (D) is a generic term and not specific to the periodic table structure. Therefore, the correct term for the horizontal rows of the periodic table is periods.

Correct Answer: A

Rationale: Silicon is a metalloid because it exhibits properties of both metals and non-metals. It is a semiconductor, has a shiny appearance, and conducts electricity to some extent. Lead is a metal, helium is a noble gas, and aluminum is a metal. Therefore, the correct answer is A: Silicon.

Correct Answer: B

Rationale: The correct answer is B: It releases heat. In an exothermic reaction, energy is released in the form of heat to the surroundings. This results in a temperature increase in the surrounding environment. The other choices are incorrect because: A: It absorbs heat - This is a characteristic of an endothermic reaction, where heat is absorbed from the surroundings. C: It remains neutral - This does not describe the nature of an exothermic reaction, which involves the release of heat. D: It requires energy input - This is more in line with an endothermic reaction, where energy input is needed to drive the reaction.