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: 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.

Correct Answer: A

Rationale: The correct answer is A: 92. Uranium-235 has an atomic number of 92, which represents the number of protons in its nucleus. Neutrons are calculated by subtracting the atomic number from the mass number (235 - 92 = 143), so there are 143 neutrons in uranium-235. This makes option A the correct choice. Options B, C, and D are incorrect because they do not accurately reflect the number of neutrons in uranium-235 based on its atomic number and mass number.

Correct Answer: B

Rationale: Failed to generate a rationale after 5 retries.