HESI A2
Chemistry HESI A2 Practice Test
1. A salt solution has a molarity of 5 M. How many moles of this salt are present in 0 L of this solution?
- A. 0
- B. 1.5
- C. 2
- D. 3
Correct answer: A
Rationale: Molarity is defined as the number of moles of solute per liter of solution. A molarity of 5 M indicates there are 5 moles of salt in 1 liter of the solution. Since the volume of the solution is 0 liters, multiplying the molarity by 0 liters results in 0 moles of salt (5 moles/L x 0 L = 0 moles). Therefore, the correct answer is 0. Option B, 1.5, is incorrect because it doesn't consider the volume being 0 liters. Options C and D, 2 and 3 respectively, are also incorrect as they do not account for the zero volume of the solution. Hence, there are no moles of salt present in 0 liters of the solution.
2. 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.
3. What is the normal body temperature in °C?
- A. 36°C
- B. 37°C
- C. 35°C
- D. 40°C
Correct answer: B
Rationale: The normal body temperature for humans is 37°C. This temperature is considered average and is a standard reference point for assessing an individual's health status. It is essential for the body to maintain this temperature to ensure optimal functioning of various physiological processes. Choice A (36°C) is incorrect as it is slightly below the normal body temperature. Choice C (35°C) is also incorrect as it is significantly lower than the normal body temperature. Choice D (40°C) is incorrect as it is significantly higher than the normal body temperature and would indicate a fever or other health issue.
4. 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.
5. When an acid is added to a base, water and a salt form. What kinds of bonds form in these two compounds?
- A. Liquid and metallic
- B. Polar and nonpolar covalent
- C. Polar covalent and ionic
- D. Ionic only
Correct answer: C
Rationale: In water, the bond formed between the oxygen atom and the hydrogen atoms is a polar covalent bond. The oxygen atom attracts the shared electrons more strongly, creating a partial negative charge on the oxygen and a partial positive charge on the hydrogen atoms. In the salt formed, the bond between the metal cation and the nonmetal anion is predominantly an ionic bond. The metal cation donates electrons to the nonmetal anion, resulting in the formation of oppositely charged ions that are held together by electrostatic attractions. Choices A and B are incorrect because water and salts do not form bonds that are liquid and metallic, or polar and nonpolar covalent. Choice D is incorrect as it oversimplifies the types of bonds present in water and salts, failing to differentiate between the covalent bond in water and the ionic bond in the salt.
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