Chemistry HESI A2 Practice Test

Correct Answer: A

Rationale: Failed to generate a rationale after 5 retries.

Correct Answer: A

Rationale: Failed to generate a rationale after 5 retries.

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 because the rate of diffusion is inversely proportional to the square root of the molar mass. Therefore, if gas A has four times the molar mass of gas B, gas A would diffuse at half the rate of gas B. This is because the square root of 4 is 2, indicating that gas A would diffuse at a rate that is half of gas B. Choice B is incorrect because if gas A has four times the molar mass of gas B, it would not diffuse at twice the rate of gas B. Choice C is incorrect because gas A would not diffuse at a quarter the rate of gas B. Choice D is incorrect because gas A would not diffuse at four times the rate of gas B.

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.