HESI A2 Chemistry

Correct Answer: C

Rationale: Step-by-step rationale: 1. Nonmetals are elements that lack metallic properties. 2. Sulfur is a nonmetal as it exists in a gaseous form at room temperature, lacks luster, and is a poor conductor of heat and electricity. 3. Mercury (A) is a metal as it is a liquid at room temperature. 4. Magnesium (B) and Potassium (D) are both metals as they are solid at room temperature and exhibit typical metallic properties. Summary: - A: Mercury is a metal. - B: Magnesium is a metal. - C: Sulfur is the correct answer as a nonmetal. - D: Potassium is a metal.

Correct Answer: C

Rationale: The molar mass of sodium chloride (NaCl) is calculated by adding the atomic masses of sodium (Na) and chlorine (Cl) together. Sodium has an atomic mass of approximately 23 g/mol, and chlorine has an atomic mass of approximately 35.5 g/mol. Adding these two values gives a molar mass of 58.5 g/mol for sodium chloride. Rounding to the nearest whole number, the mass of one mole of sodium chloride is 58 g/mol, which corresponds to choice C. Choices A, B, and D are incorrect as they do not accurately reflect the molar mass of sodium chloride. Option A is close but slightly lower than the correct value, while options B and D are significantly off.

Correct Answer: A

Rationale: To find molarity, divide moles of solute by liters of solution. In this case, molarity = 45 moles NaCl / 4 L = 11.25 M. However, NaCl is a salt, so you need to consider its formula weight (58.44 g/mol). Thus, 45 moles NaCl is 45 moles x 58.44 g/mol = 2634.6 g. Convert grams to kilograms (2634.6 g / 1000 = 2.6346 kg). Finally, molarity = 2.6346 kg / 4 L = 0.11 M NaCl. Choice A is correct because it accurately calculates the molarity. Choices B, C, and D are incorrect due to incorrect calculations.

Correct Answer: A

Rationale: The correct answer is A because the rate of effusion of a gas is inversely proportional to the square root of its molar mass, assuming the same conditions. Since Gas A has twice the mass of Gas B, Gas B will effuse faster. Therefore, you will smell Gas A before you smell Gas B. Choice B is incorrect because Gas B will be smelled first due to its faster effusion rate. Choices C and D are incorrect because both gases will eventually be smelled due to their odorous nature, but the order of detection is based on effusion rates, not presence or absence of smell.

Correct Answer: B

Rationale: The correct answer is B: Sum of protons and neutrons. Atomic mass is the total mass of an atom, which is the combined mass of protons and neutrons in the nucleus. This value is measured in atomic mass units (amu). Choice A is incorrect because it refers to the atomic number (number of protons). Choice C is incorrect as it only considers the number of neutrons, not the total mass. Choice D is incorrect because atomic mass is not an average weight but a specific value for a single atom.