HESI A2 Chemistry

Correct Answer: C

Rationale: The correct answer is C: black. Red and white phosphorus are well-known allotropes. Black phosphorus is another important allotrope with a layered structure. It is stable at room temperature and has unique electronic properties. Green, gray, and silver are not commonly recognized allotropic forms of phosphorus, making them incorrect choices.

Correct Answer: B

Rationale: The correct answer is B (-1) because in NaOH, Na is a group 1 metal with an oxidation state of +1, and H is typically +1. Since the compound is neutral, the oxidation state of oxygen must be -1 to balance the charges. Choice A (-2) is incorrect because oxygen rarely has an oxidation state of -2 in compounds. Choice C (0) is incorrect as oxygen is not in its elemental form. Choice D (+2) is incorrect as it is not a common oxidation state for oxygen in compounds.

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: C

Rationale: The correct answer is C: Between 6 and 8. Tap water is typically slightly alkaline, with a pH range between 6.5 and 8.5. This is considered neutral to slightly basic, as pure water has a pH of 7. The pH scale ranges from 0 to 14, with 7 being neutral. Choices A, B, and D are incorrect because tap water is not highly acidic (A), acidic (B), or highly alkaline (D). Tap water falls within the slightly basic range on the pH scale.

Correct Answer: B

Rationale: The correct answer is B: Acid. Acids are hydrogen or proton donors, corrosive to metals, turn blue litmus paper red (indicating acidity), and become less acidic when mixed with a base due to neutralization reaction. Bases (choice A) are proton acceptors and do not exhibit these characteristics. Salts (choice C) are formed from the reaction between an acid and a base and do not fit all the given criteria. Hydroxides (choice D) are bases and do not donate protons or exhibit the acidic properties described.