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: Synthesis reaction. In a synthesis reaction, two or more reactants combine to form a single product. This type of reaction is characterized by the formation of a more complex molecule from simpler ones. The other choices are incorrect because: B: Combustion reaction involves the rapid combination of a substance with oxygen, producing heat and light. C: Decomposition reaction involves the breakdown of a compound into simpler substances. D: Double displacement reaction involves the exchange of ions between two compounds to form two new compounds.

Correct Answer: B

Rationale: The correct answer is B: Ionic bonds. Ionic compounds are held together by the attraction between positively and negatively charged ions. This attraction is created when one atom donates electrons to another, forming ions with opposite charges that attract each other. Covalent bonds (A) involve sharing electrons, not transferring them. Hydrogen bonds (C) are weaker interactions between hydrogen atoms and electronegative atoms like oxygen or nitrogen. Metallic bonds (D) involve the delocalized sharing of electrons in a sea of electrons within a metal structure.

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: Oxygen. During photosynthesis, plants use carbon dioxide and water to produce glucose and oxygen. Oxygen is released as a byproduct of this process through the stomata in plant leaves. Carbon dioxide (A) is actually used up during photosynthesis, not released. Nitrogen (C) and Helium (D) are not involved in the process of photosynthesis.