HESI A2 Chemistry Questions

Correct Answer: A

Rationale: The correct answer is A: 7. In a neutral solution, the concentration of H+ ions equals the concentration of OH- ions, resulting in a pH of 7. This signifies a balance between acidity and alkalinity. Choice B (0) is incorrect as it represents a strong acid, choice C (14) is incorrect as it represents a strong base, and choice D (4) is incorrect as it indicates an acidic solution.

Correct Answer: B

Rationale: The correct answer is B: Nitrogen. Nitrogen makes up about 78% of Earth's atmosphere, making it the main component of air. Oxygen (A) is the second most abundant gas in the atmosphere at around 21%. Carbon dioxide (C) is present in much lower concentrations, around 0.04%. Argon (D) is also a minor component of air, at less than 1%. Nitrogen's high percentage in the atmosphere is the reason it is considered the main component of air.

Correct Answer: A

Rationale: The correct answer is A: Neutralization reaction. In this reaction, an acid and a base combine to form water and a salt. This process involves the transfer of protons from the acid to the base, resulting in the formation of water and a salt. Neutralization reactions are characterized by the formation of a neutral product (water) from the acidic and basic reactants. Option B: Decomposition reaction involves a compound breaking down into simpler substances. Option C: Combustion reaction involves a substance reacting with oxygen to produce heat and light. Option D: Redox reaction involves the transfer of electrons between reactants. These options do not accurately describe the reaction between an acid and a base to form water and salt.

Correct Answer: D

Rationale: The correct answer is D: Baking soda. Baking soda, or sodium bicarbonate, has a pH value greater than 7, typically around 8.4 when dissolved in water. This is because it is a basic compound that releases hydroxide ions when dissolved in water, resulting in a pH above 7. In contrast, choices A, B, and C have pH values below 7. Water (choice A) is neutral with a pH of 7, vinegar (choice B) is acidic with a pH below 7, and lemon juice (choice C) is also acidic due to the presence of citric acid. Therefore, baking soda is the only substance among the choices that has a pH value greater than 7.

Correct Answer: B

Rationale: The correct answer is B: Fluorine. Halogens are a group of elements in the periodic table that include Fluorine, Chlorine, Bromine, Iodine, and Astatine. They are highly reactive nonmetals with seven valence electrons, making them very electronegative. Fluorine specifically is the most reactive and electronegative element, commonly found in compounds like fluoride toothpaste. A: Oxygen is not a halogen. It is a nonmetal but belongs to the chalcogen group in the periodic table. C: Sodium is a metal and belongs to the alkali metal group, not a halogen. D: Carbon is a nonmetal but is not a halogen. It belongs to the p-block elements on the periodic table.