HESI A2
HESI A2 Chemistry
1. What is atomic mass?
- A. Number of protons in an atom
- B. Sum of protons and neutrons
- C. Number of neutrons in an atom
- D. Average weight of an element
Correct answer: B
Rationale: Atomic mass, also known as atomic weight, is the sum of the number of protons and neutrons in an atom. It represents the average mass of an atom of an element, taking into account the different isotopes and their relative abundance. Neutrons contribute to the atomic mass alongside protons, while the number of neutrons alone is not the definition of atomic mass. Choice A is incorrect because it refers only to the number of protons, not the complete atomic mass. Choice C is incorrect as it focuses solely on the number of neutrons, excluding the contribution of protons. Choice D is incorrect as it mentions the 'average weight of an element,' which is related to atomic mass but does not encapsulate the specific definition of atomic mass as the sum of protons and neutrons.
2. What is the name of the group of elements that contains chlorine, fluorine, and iodine?
- A. Alkali metals
- B. Halogens
- C. Transition metals
- D. Noble gases
Correct answer: B
Rationale: The correct answer is 'Halogens.' Halogens are a group of elements that include chlorine, fluorine, and iodine. These elements are part of Group 17 in the periodic table. They share similar properties such as high reactivity and the ability to readily form compounds. Choice A, 'Alkali metals,' is incorrect as alkali metals are found in Group 1 of the periodic table, which includes elements like lithium and sodium. Choice C, 'Transition metals,' is incorrect as transition metals are located in the middle section of the periodic table, not in Group 17. Choice D, 'Noble gases,' is incorrect as noble gases are in Group 18 and include elements like helium and neon, which are chemically inert.
3. Balance this equation: Fe + Cl2 → FeCl3
- A. 2Fe + 2Cl2 → 2FeCl3
- B. 2Fe + 3Cl2 → 2FeCl3
- C. 3Fe + 2Cl2 → 3FeCl3
- D. 3Fe + 3Cl2 → 6FeCl3
Correct answer: B
Rationale: In the given equation, Fe combines with Cl to form FeCl3. To balance the equation, we need to have the same number of each element on both sides. Since Cl is represented as Cl2 in the equation, we need 3 Cl2 molecules to balance Fe, resulting in 2Fe + 3Cl2 → 2FeCl3. Choice A is incorrect because it only balances Fe but not Cl2. Choice C is incorrect as it balances Fe but not Cl2. Choice D is incorrect as it balances Fe but overbalances Cl2.
4. What is the pH of a neutral solution?
- A. 7
- B. 0
- C. 14
- D. 4
Correct answer: A
Rationale: The correct answer is A: 7. A neutral solution has a pH of 7. In the pH scale, values below 7 are acidic, 7 is neutral, and values above 7 are basic. Therefore, a solution with a pH of 7 is considered neutral as it is neither acidic nor basic. Choices B, C, and D are incorrect because a pH of 0 indicates a strong acid, a pH of 14 indicates a strong base, and a pH of 4 indicates an acidic solution. None of these values represent a neutral solution.
5. What are bases or alkaline solutions known as?
- A. Hydrogen acceptors
- B. Solutions of low pH
- C. Hydrogen donors
- D. Amphoteric
Correct answer: A
Rationale: Bases or alkaline solutions are known as 'hydrogen acceptors.' They accept protons (H+) in chemical reactions, as opposed to acids that donate protons. This property allows bases to neutralize acids and form salts. Choice B, 'Solutions of low pH,' is incorrect because bases have high pH values, not low. Choice C, 'Hydrogen donors,' is incorrect as bases do not donate protons but accept them. Choice D, 'Amphoteric,' refers to substances that can act as both acids and bases, which is not the definition of bases. Therefore, the correct answer is A.
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