HESI A2
Chemistry HESI A2 Practice Test
1. Which ion would you expect to dominate in water solutions of bases?
- A. MgCl₂
- B. 2HCl
- C. H⁺
- D. OH⁻
Correct answer: D
Rationale: In water solutions of bases, the dominant ion would be OH⁻ (hydroxide ion). Bases release OH⁻ ions when dissolved in water, increasing the concentration of hydroxide ions and leading to a higher pH. This is in contrast to acids, which release H⁺ ions. Therefore, in water solutions of bases, the presence of OH⁻ ions signifies the basic nature of the solution. Choices A, B, and C are incorrect because MgCl₂ is a salt, 2HCl is a compound consisting of two hydrogen ions and one chloride ion, and H⁺ represents a hydrogen ion typically associated with acids, not bases.
2. Which element would you expect to be least reactive?
- A. Li
- B. Cr
- C. Nd
- D. Xe
Correct answer: D
Rationale: Xenon (Xe) is a noble gas located in Group 18 of the periodic table. Noble gases are known for their stable and unreactive nature due to having a full outer shell of electrons. Therefore, xenon would be expected to be the least reactive among the given elements. Choice A (Li) is a metal in Group 1 of the periodic table, which tends to be reactive, especially with water. Choice B (Cr) is a transition metal known for its reactivity in some forms. Choice C (Nd) is a rare earth element, which can exhibit varying reactivity depending on the compound or environment.
3. To the nearest whole number, what is the mass of one mole of water?
- A. 16 g/mol
- B. 18 g/mol
- C. 20 g/mol
- D. 22 g/mol
Correct answer: B
Rationale: The molar mass of water (H₂O) is calculated by adding the atomic masses of two hydrogen atoms (each with a molar mass of approximately 1 g/mol) and one oxygen atom (with a molar mass of approximately 16 g/mol). Therefore, the molar mass of water is approximately 18 g/mol, making choice B the correct answer. Choice A (16 g/mol) is incorrect because it represents the molar mass of oxygen, not water. Choices C (20 g/mol) and D (22 g/mol) are incorrect as they do not correspond to the molar mass of water.
4. What is the charge of an alpha particle?
- A. -1
- B. +1
- C. +2
- D. No charge
Correct answer: C
Rationale: An alpha particle consists of two protons and two neutrons, resulting in a total charge of +2 due to the presence of two positively charged protons. Therefore, the correct answer is C, indicating a charge of +2. Choices A, B, and D are incorrect because an alpha particle is positively charged due to the two protons it contains, resulting in a charge of +2.
5. 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.
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