HESI A2
HESI A2 Chemistry
1. What is the correct electron configuration for magnesium?
- A. 1s² 2s²
- B. 1s² 2s² 2p⁶
- C. 1s² 2s² 2p⁶ 3s²
- D. 1s² 2s² 2p⁶ 3s² 3p¹
Correct answer: C
Rationale: The electron configuration of an element is determined by following the Aufbau principle, which states that electrons fill orbitals starting from the lowest energy level. Magnesium has an atomic number of 12, meaning it has 12 electrons. The electron configuration of magnesium fills the 1s, 2s, 2p, and 3s orbitals to accommodate all 12 electrons. Therefore, the correct electron configuration for magnesium is 1s² 2s² 2p⁶ 3s². Choice A is incorrect as it only includes 4 electrons and stops at the 2s orbital. Choice B is incorrect as it includes 8 electrons and stops at the 2p orbital. Choice D is incorrect as it includes 13 electrons and extends to the 3p orbital, which is beyond the actual electron configuration of magnesium.
2. What is the correct formula for silver hydroxide?
- A. AgO
- B. AgOH
- C. AgH
- D. AgH₂O
Correct answer: B
Rationale: The correct formula for silver hydroxide is AgOH. Silver hydroxide is formed by the combination of the silver ion (Ag⁺) with the hydroxide ion (OH⁻) to create AgOH. It is essential to note that the hydroxide ion consists of one oxygen and one hydrogen atom, thus the formula AgOH. Choices A, C, and D are incorrect as they do not accurately represent the composition of silver hydroxide.
3. What defines a balanced chemical equation?
- A. An equation where the number of atoms of each element is the same on both sides
- B. An equation where there are more products than reactants
- C. An equation where the number of molecules is balanced
- D. An equation with equal masses on both sides
Correct answer: A
Rationale: A balanced chemical equation is one in which the number of atoms of each element is the same on both sides. This balance ensures the law of conservation of mass is upheld, where the total mass of the reactants equals the total mass of the products. Options B, C, and D are incorrect. Option B is incorrect as a balanced equation has an equal number of products and reactants. Option C is incorrect as balancing refers to the number of atoms, not molecules. Option D is incorrect as balancing is based on the number of atoms, not masses. Therefore, option A is the correct choice as it accurately describes a balanced chemical equation.
4. What are the three types of intermolecular forces?
- A. Ionic, covalent, hydrogen
- B. Hydrogen bonding, dipole interactions, dispersion forces
- C. Van der Waals, ionic, covalent
- D. Hydrogen, Van der Waals, dispersion forces
Correct answer: B
Rationale: The three types of intermolecular forces are hydrogen bonding, dipole interactions, and dispersion forces. Option A includes ionic and covalent bonds, which are intramolecular forces, not intermolecular. Option C includes van der Waals forces, which encompass dipole interactions and dispersion forces, but also includes ionic and covalent bonds. Option D is close but misses dipole interactions, which are distinct from hydrogen bonding and dispersion forces. Therefore, option B is the correct choice as it includes the three specific types of intermolecular forces.
5. How many electrons are in a neutral atom of neon?
- A. 9
- B. 10
- C. 11
- D. 12
Correct answer: B
Rationale: The atomic number of neon is 10, which represents the number of protons in its nucleus. In a neutral atom, the number of electrons is equal to the number of protons to maintain electrical neutrality. Therefore, a neutral atom of neon contains 10 electrons, matching the 10 protons within the nucleus. Choice A (9 electrons) is incorrect as it doesn't correspond to the atomic number of neon. Choices C (11 electrons) and D (12 electrons) are also incorrect as they do not align with the correct atomic number of neon.
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