Chemistry HESI A2 Practice Test

Correct Answer: B

Rationale: The correct answer is B: 8. Carbon-14 has 6 protons, so to find the number of neutrons, subtract the atomic number from the atomic mass. Carbon-14 has an atomic mass of approximately 14, so 14 (atomic mass) - 6 (protons) = 8 neutrons. Choice A (10) is incorrect because it doesn't correspond to the correct calculation for carbon-14. Choice C (6) is the number of protons, not neutrons. Choice D (12) is incorrect as it does not align with the calculated number of neutrons in carbon-14.

Correct Answer: D

Rationale: The correct answer is D: Time. Time does not directly impact rates of reaction; rather, it is the duration over which a reaction occurs. Temperature affects reaction rates by increasing kinetic energy, surface area by exposing more reactant molecules, and pressure by affecting collision frequency. Time is not an influencing factor in itself, but the overall reaction rate may depend on the time taken for the reaction to complete.

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 answer is B: Days-long. Medical isotopes used in medicine typically have a short half-life to minimize radiation exposure to patients. A days-long half-life strikes a balance between decay rate and practical usability in medical procedures. Choice A (Seconds-long) would be too short for practical use. Choices C (Years-long) and D (Many years long) would result in prolonged radiation exposure, increasing health risks for patients.

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.