Chemistry HESI A2 Practice Test

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. Amino acids typically contain an amine group (R-NH2) and a carboxylic acid group (R-COOH). The amine group acts as a base, accepting protons, while the carboxylic acid group acts as an acid, donating protons. This combination allows amino acids to participate in acid-base reactions and form peptide bonds in proteins. Choice B is incorrect because R-CHO is an aldehyde group, not typically found in amino acids. Choice C is incorrect because R-OH is a hydroxyl group and R-COOR is an ester group, neither of which are characteristic functional groups of amino acids. Choice D is incorrect as R-O-R is an ether group, not commonly present in amino acids, and R-COOH alone is not sufficient as amino acids also require an amine group.

Correct Answer: B

Rationale: The correct answer is B: < 7. Acids have a pH below 7 because they release hydrogen ions when dissolved in water, making the solution acidic. A pH of 7 is neutral, not acidic. Choices A (7.5) and C (> 7) are incorrect because they indicate values above 7, which would be alkaline/basic. Choice D (7) is incorrect because it represents a neutral pH, not acidic. Thus, the correct answer is B as it accurately represents the pH range of acids.

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.