HESI A2
Chemistry HESI A2 Quizlet
1. Which number represents the number of protons in an element?
- A. Atomic mass
- B. Mass number
- C. Atomic number
- D. Proton number
Correct answer: C
Rationale: The correct answer is C: Atomic number. The atomic number corresponds to the number of protons in an element. Protons are positively charged subatomic particles found in the nucleus of an atom. Each element has a unique atomic number, which defines its identity based on the number of protons it contains. Choice A, Atomic mass, is incorrect as it refers to the average mass of an atom of an element. Choice B, Mass number, represents the total number of protons and neutrons in an atom's nucleus. Choice D, Proton number, is not a commonly used term in chemistry to indicate the number of protons.
2. To the nearest whole number, what is the mass of one mole of sodium chloride?
- A. 36 g/mol
- B. 43 g/mol
- C. 58 g/mol
- D. 72 g/mol
Correct answer: C
Rationale: The molar mass of sodium chloride (NaCl) is calculated by adding the atomic masses of sodium (Na) and chlorine (Cl). The atomic mass of sodium is approximately 23 g/mol and chlorine is approximately 35.5 g/mol. Adding these two atomic masses gives us a molar mass of approximately 58 g/mol for sodium chloride (NaCl). Therefore, the correct answer is C, 58 g/mol. Choice A (36 g/mol) is incorrect as it does not account for the individual atomic masses of sodium and chlorine. Choice B (43 g/mol) and choice D (72 g/mol) are also incorrect as they do not reflect the accurate molar mass of sodium chloride.
3. What is another name for aqueous HI?
- A. hydroiodic acid
- B. hydrogen monoiodide
- C. hydrogen iodide
- D. hydriodic acid
Correct answer: D
Rationale: The correct name for aqueous HI is 'hydriodic acid.' When hydrogen iodide (HI) dissolves in water, it forms hydriodic acid. Therefore, 'hydriodic acid' is the appropriate term for aqueous HI. Choice A, 'hydroiodic acid,' is incorrect as it does not reflect the nature of the compound in the aqueous state. Choice B, 'hydrogen monoiodide,' is not a widely recognized term for this compound. Choice C, 'hydrogen iodide,' is the name for HI in the gaseous state, not when it's dissolved in water.
4. What term refers to the average of the masses of each of its isotopes as they occur in nature?
- A. Atomic number
- B. Mass number
- C. Atomic mass
- D. Neutron number
Correct answer: C
Rationale: The correct answer is atomic mass. Atomic mass is the weighted average of the masses of an element's isotopes. It takes into account the abundance of each isotope in nature to provide a more accurate representation of the element's overall mass. Choice A, atomic number, represents the number of protons in an atom. Choice B, mass number, refers to the total number of protons and neutrons in an atom's nucleus. Choice D, neutron number, specifically focuses on the count of neutrons in an atom's nucleus. These choices do not directly relate to the average mass of isotopes as asked in the question.
5. What type of intermolecular force is a dipole attraction?
- A. Strong
- B. Weak
- C. Medium
- D. Very strong
Correct answer: B
Rationale: A dipole attraction is considered a weak intermolecular force. It occurs between molecules with permanent dipoles, where the positive end of one molecule is attracted to the negative end of another molecule. While dipole-dipole interactions are stronger than dispersion forces, they are weaker than hydrogen bonding or ion-dipole interactions. Therefore, the correct answer is 'Weak.' Choices A, C, and D are incorrect because dipole attractions are not classified as strong, medium, or very strong intermolecular forces, but rather fall into the category of weak intermolecular forces.
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