HESI A2 Chemistry

Correct Answer: C

Rationale: The correct answer is C, pink. Phenolphthalein is colorless in acidic solutions and turns pink in the presence of a base due to a shift in pH causing a structural change. This color change is a result of the molecule's ability to act as a pH indicator, making it ideal for titrations. Choice A, clear, is incorrect as phenolphthalein is not colorless in the presence of an acid. Choice B, blue, is incorrect as phenolphthalein does not turn blue in any pH range. Choice D, red, is incorrect as phenolphthalein turns pink, not red, in the presence of a base.

Correct Answer: B

Rationale: The correct answer is B: 19 protons. Potassium's atomic number is 19, which represents the number of protons in its nucleus. Protons are positively charged particles in an atom. Option A (18) is incorrect as it does not match the atomic number of Potassium. Options C (20) and D (21) are also incorrect as they do not correspond to Potassium's atomic number. Thus, the correct answer is B (19) based on the periodic table.

Correct Answer: B

Rationale: The correct answer is B: Butane. In this compound, CH₃-CH₂-CH₂-CH₃, there are four carbon atoms connected in a straight chain, making it a butane. The prefix "but-" indicates that there are four carbon atoms, and the suffix "-ane" indicates that the compound contains only single bonds between the carbon atoms. Therefore, the correct name is Butane. Choice A: Cyclobutane is incorrect because it would be a cyclic compound with four carbon atoms forming a ring. Choice C: Butene is incorrect because it would have a double bond between two carbon atoms, making it an alkene. Choice D: Butyne is incorrect because it would have a triple bond between two carbon atoms, making it an alkyne.

Correct Answer: A

Rationale: The correct answer is A: Zinc sulfate. ZnSO₄ consists of zinc (Zn) and sulfate (SO₄) ions. The name of an ionic compound follows the pattern of cation name + anion name with appropriate suffixes. In this case, "sulfate" is the correct name for the polyatomic ion SO₄, so the compound is named zinc sulfate. Incorrect choices: B: Zinc sulfide - Sulfide is a different anion (S²⁻) than sulfate. C: Zinc sulfur - Incorrect as it doesn't specify the anion involved. D: Zinc oxide - Oxide is a different anion (O²⁻) than sulfate.

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.