HESI A2 Chemistry

Correct Answer: C

Rationale: The correct balanced equation is 2Fe + O₂ → 2FeO. This is because there is 1 Fe atom on each side, 2 O atoms on each side, and the ratio of Fe to O is 2:2. Choice A has incorrect coefficients for Fe and O, choice B has an incorrect ratio of Fe to O, and choice D also has incorrect coefficients for Fe and O. Thus, the correct answer is C as it maintains the balance of atoms on both sides of the equation.

Correct Answer: B

Rationale: The correct answer is B: London dispersion force. This is because London dispersion forces are the weakest intermolecular force, resulting in lower boiling points compared to the other options. London dispersion forces are temporary, induced forces caused by momentary fluctuations in electron distribution within molecules. Dipole-dipole interactions (A), Keesom interactions (C), and hydrogen bonding (D) are stronger intermolecular forces that require specific molecular properties such as permanent dipoles or hydrogen bonding, leading to higher boiling points. Therefore, London dispersion forces would result in the lowest boiling point among the options provided.

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 formula for potassium chloride is KCl. "K" represents potassium and "Cl" represents chloride. Potassium is a metal with a +1 charge, while chloride is a non-metal with a -1 charge. When these two ions combine, they form a neutral compound with a 1:1 ratio, resulting in the formula KCl. Choice A (NaCl) is incorrect because "Na" represents sodium, not potassium. Choice C (KCl) is also incorrect because it is the same as the correct answer. Choice D (ClK) is incorrect as the order of elements in a chemical formula matters, and in this case, it should be KCl to represent potassium chloride accurately.

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.