HESI A2
HESI A2 Chemistry Questions
1. Which element has the highest atomic number?
- A. Uranium
- B. Hydrogen
- C. Radon
- D. Bismuth
Correct answer: A
Rationale: The correct answer is Uranium. The atomic number represents the number of protons in an atom's nucleus. Among the options provided, Uranium has the highest atomic number, which is 92. Hydrogen has an atomic number of 1, Radon has an atomic number of 86, and Bismuth has an atomic number of 83. Therefore, Uranium is the element with the highest atomic number in the given choices.
2. What is the correct formula for iron III oxide?
- A. IO
- B. FeS
- C. Fe₂O₃
- D. OFe₂₃
Correct answer: C
Rationale: The correct formula for iron III oxide is Fe2O3. In this formula, Fe represents iron and O represents oxygen. Iron III oxide consists of two iron (Fe) ions combined with three oxygen (O) ions. Thus, the correct formula is Fe2O3. Choice A (IO) is incorrect as it does not represent the correct combination of iron and oxygen ions. Choice B (FeS) is incorrect as it represents iron sulfide, not iron III oxide. Choice D (OFe₂₃) is incorrect as it does not follow the correct chemical nomenclature for iron III oxide.
3. What is the correct name of MgO?
- A. Manganese oxide
- B. Magnesium oxide
- C. Magnesium oxate
- D. Magnesium hydroxide
Correct answer: B
Rationale: The correct name of MgO is Magnesium oxide. Mg represents the chemical symbol for magnesium, and O represents the chemical symbol for oxygen. When these elements combine, they form magnesium oxide. Option A, Manganese oxide, is incorrect as it refers to a compound of manganese and oxygen, not magnesium. Option C, Magnesium oxate, is not a valid chemical compound name. Option D, Magnesium hydroxide, refers to a different compound consisting of magnesium, oxygen, and hydrogen.
4. What does the mass number minus the atomic number equal?
- A. Number of electrons
- B. Number of neutrons
- C. Number of protons
- D. Number of isotopes
Correct answer: B
Rationale: The mass number of an atom represents the total number of protons and neutrons in its nucleus. The atomic number indicates the number of protons in the nucleus. The difference between the mass number and the atomic number provides the number of neutrons present in the nucleus of an atom. Therefore, mass number minus atomic number equals the number of neutrons. Choice A is incorrect because the number of electrons is not determined by the mass number and atomic number. Choice C is incorrect as it represents the number of protons, not the difference between the mass number and atomic number. Choice D is incorrect as isotopes refer to atoms of the same element with different numbers of neutrons, not the difference between mass number and atomic number.
5. Which law states that matter can neither be created nor destroyed during a chemical reaction?
- A. Law of Conservation of Energy
- B. Law of Conservation of Mass
- C. Law of Constant Composition
- D. Law of Multiple Proportions
Correct answer: B
Rationale: The correct answer is B, the Law of Conservation of Mass. This law, formulated by Antoine Lavoisier, states that matter cannot be created or destroyed in a chemical reaction. It is a fundamental principle in chemistry that explains the preservation of mass during chemical reactions, indicating that the total mass of the reactants is equal to the total mass of the products. The other choices are incorrect because: A: The Law of Conservation of Energy states that energy cannot be created or destroyed, not matter. C: The Law of Constant Composition refers to compounds having the same composition by mass regardless of their source or how they were prepared, not about the conservation of matter in reactions. D: The Law of Multiple Proportions describes the ratios in which elements combine to form compounds, not the conservation of mass.
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