Chemistry HESI A2 Practice Test

Correct Answer: C

Rationale: The given chemical equation shows aluminum replacing hydrogen in sulfuric acid, which is a single replacement reaction. In this type of reaction, one element displaces another in a compound. Here, Al replaces H in H2SO4 to form Al2(SO4)3 and HNO3. The other choices are incorrect because a decomposition reaction involves a single compound breaking down into simpler substances, a synthesis reaction involves two or more substances combining to form a new compound, and a double replacement reaction involves the exchange of ions between two compounds.

Correct Answer: B

Rationale: The correct formula for silver hydroxide is AgOH. Silver is a transition metal with a +1 charge, and hydroxide is OH⁻. To balance the charges, one silver ion combines with one hydroxide ion to form AgOH. Choice A (AgO) is incorrect because it does not include the hydroxide ion. Choice C (AgH) is incorrect as it suggests silver bonding with hydrogen, which is not the case. Choice D (AgH₂O) is incorrect as it implies silver bonding with water molecules, which is not the formula for silver hydroxide.

Correct Answer: B

Rationale: The molar mass of a substance is the mass of one mole of that substance. The molar mass of water (H2O) can be calculated by adding the atomic masses of its components (2 hydrogen atoms + 1 oxygen atom). Hydrogen's atomic mass is approximately 1 g/mol, and oxygen's atomic mass is approximately 16 g/mol. Therefore, the molar mass of water is 2(1) + 16 = 18 g/mol. This makes choice B (18 g/mol) the correct answer. Choices A, C, and D are incorrect because they do not reflect the accurate molar mass calculation of water based on the atomic masses of its components.

Correct Answer: A

Rationale: The correct answer is A (pH 3) for lemon juice. Lemon juice is acidic due to citric acid content, resulting in a low pH value. The pH scale ranges from 0-14, with 7 being neutral. Lemon juice with a pH of 3 is considered highly acidic. Choice B (pH 5) is less acidic than choice A. Choice C (pH 7) is neutral, which is not characteristic of lemon juice. Choice D (pH 9) is alkaline, opposite to the acidity of lemon juice. Lemon juice's low pH value contributes to its sour taste and preservation properties.

Correct Answer: A

Rationale: The correct answer is A: 0 moles. In the given scenario, the volume of the solution is 0 L, which means there is no solution to contain any amount of salt. Molarity is the concentration of a solution in moles of solute per liter of solution. Since the volume is 0 L, there are no moles of salt present. Choice B, C, and D are incorrect because they suggest there are moles of salt present, which is not possible when the volume of the solution is 0 L.