HESI A2 Chemistry

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 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: 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: D

Rationale: The correct answer is D: ionization energy. Ionization energy is the energy needed to remove an electron from an atom. The outermost electron requires the least amount of energy to remove as it is farthest from the nucleus. This process results in the formation of a positively charged ion. Explanation: 1. Covalent bonding (A) refers to the sharing of electrons between atoms, not the energy required to remove an electron. 2. Electronegativity (B) is the ability of an atom to attract electrons in a chemical bond, not the energy needed to remove an electron. 3. Atomic radius (C) is the size of an atom, which does not directly relate to the energy required to remove an electron.

Correct Answer: D

Rationale: The correct answer is D, H₂O. Water (H₂O) contains a polar covalent bond. This is because oxygen is more electronegative than hydrogen, creating an unequal sharing of electrons, resulting in a partial negative charge on oxygen and a partial positive charge on hydrogen. This polarity makes water a universal solvent and gives rise to properties like surface tension and hydrogen bonding. Choices A, B, and C (O, F, Br) do not form polar covalent bonds as they do not have significantly different electronegativities compared to the other element in the bond.