HESI A2 Chemistry Questions

Correct Answer: C

Rationale: The correct answer is C: Argon. Noble gases are elements in Group 18 of the periodic table with full valence electron shells, making them stable and non-reactive. Argon is a noble gas with 8 valence electrons, fulfilling the octet rule. Hydrogen (A) is a nonmetal in Group 1, Fluorine (B) is a halogen in Group 17, and Nitrogen (D) is a nonmetal in Group 15, none of which are noble gases.

Correct Answer: A

Rationale: The correct answer is A: Decomposition reaction. In a decomposition reaction, a compound is broken down into its individual components. This process involves the breaking of chemical bonds within the compound, resulting in the formation of simpler substances. This type of reaction is characterized by one reactant and multiple products. In contrast, the other choices - B: Combustion reaction, C: Neutralization reaction, and D: Single displacement reaction - do not involve the breaking down of a compound into its components but rather involve different types of chemical transformations. Combustion reaction involves the reaction of a substance with oxygen to produce heat and light, neutralization reaction involves the reaction between an acid and a base to form water and a salt, and single displacement reaction involves the replacement of one element in a compound by another element.

Correct Answer: D

Rationale: The correct answer is D: hydriodic acid. In aqueous solution, HI dissociates into H+ and I- ions, forming hydriodic acid. Choice A (hydroiodic acid) is incorrect as it does not reflect the presence of water in the compound. Choice B (hydrogen monoiodide) is incorrect as it incorrectly implies the presence of only one iodide ion. Choice C (hydrogen iodide) is incorrect as it does not specify the compound in aqueous solution. Therefore, the correct term for aqueous HI is hydriodic acid.

Correct Answer: A

Rationale: The mass number is the sum of protons and neutrons in an atom. Given 6 protons and 6 neutrons, the mass number would be 6+6=12. Electrons do not contribute significantly to the mass number. Therefore, the correct answer is A: 12. Choice B is incorrect as it adds the protons, neutrons, and electrons together. Choice C only considers the number of protons. Choice D is incorrect as it only includes the number of protons.

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.