Chemistry HESI A2 Practice Test

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: -1. In HCl, hydrogen is always assigned an oxidation state of +1. Since the overall charge of HCl is 0, the oxidation state of chlorine must be -1 to balance the charge. Chlorine is more electronegative than hydrogen and tends to gain an electron in this compound. Therefore, the oxidation state of the chlorine atom in HCl is -1. Choice A: +1 - Hydrogen is always assigned an oxidation state of +1 in compounds. Choice C: +2 - Chlorine does not have an oxidation state of +2 in HCl. Choice D: -2 - Chlorine's oxidation state is not -2 in HCl.

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: D

Rationale: The correct answer is D: OH⁻. In water solutions of bases, OH⁻ ions are dominant as they are responsible for the basic properties. Bases release OH⁻ ions when dissolved in water, leading to an increase in pH. MgCl₂ and 2HCl do not contribute to basicity as they do not release OH⁻ ions. H⁺ ions, found in strong acids, are associated with acidic properties and would not dominate in a base solution.

Correct Answer: D

Rationale: To determine how many times more acidic a substance is based on pH, we use the formula: times more acidic = 10^(pH difference). In this case, the pH difference is 3 - 5 = -2. So, times more acidic = 10^(-2) = 1/1000. Therefore, a substance with a pH of 3 is 1,000 times more acidic than a substance with a pH of 5. Choice A (8) is incorrect because it does not reflect the pH difference between 3 and 5. Choice B (2) is incorrect as it does not consider the logarithmic scale of pH. Choice C (100) is incorrect as it does not accurately calculate the pH difference and the corresponding acidity factor.