HESI A2
HESI A2 Chemistry
1. What is the boiling point of water in °C?
- A. 90°C
- B. 100°C
- C. 95°C
- D. 80°C
Correct answer: B
Rationale: The correct answer is 100°C. The boiling point of water in Celsius is 100°C, which is standard at sea level. This is the temperature at which water changes from a liquid to a gas phase under standard atmospheric pressure. Choice A (90°C), Choice C (95°C), and Choice D (80°C) are incorrect because they do not represent the standard boiling point of water at sea level.
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. How many protons does Potassium have?
- A. 18
- B. 19
- C. 20
- D. 21
Correct answer: B
Rationale: Potassium, with the atomic symbol K, has 19 protons, which is equal to its atomic number. The number of protons determines the element's identity, and in the case of Potassium, it is 19. Choice A (18) is incorrect as it does not correspond to Potassium's proton number. Choice C (20) and Choice D (21) are also incorrect as they do not match the actual number of protons in Potassium.
4. Among the following elements, which is a nonmetal?
- A. Mercury
- B. Magnesium
- C. Sulfur
- D. Potassium
Correct answer: C
Rationale: Sulfur is a nonmetal as it is located on the right side of the periodic table. Nonmetals generally exhibit properties such as being brittle, poor conductors of heat and electricity, and having lower melting points compared to metals. Mercury (A), Magnesium (B), and Potassium (D) are all metals due to their metallic properties. Mercury is a liquid metal at room temperature, Magnesium is a solid metal, and Potassium is a solid metal as well. Therefore, the correct answer is C, Sulfur.
5. What type of chemical reaction is represented by AB → A + B?
- A. Synthesis
- B. Decomposition
- C. Single replacement
- D. Double replacement
Correct answer: B
Rationale: The chemical equation AB → A + B represents a decomposition reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. In this specific reaction, compound AB is decomposed into its elements, A and B, making it a decomposition reaction. Choice A, Synthesis, involves the combination of two or more substances to form a more complex product, which is not the case here. Choices C and D, Single replacement and Double replacement, involve the exchange of ions between compounds or elements, which is not happening in the given reaction.
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