Nokea
An atom of oxygen has more electrons than a neutral oxygen atom. What is this called?
- A. Isotope
- B. Ion
- C. Both are correct
- D. None of the above
Correct Answer: B
Rationale: The correct answer is 'B: Ion.' An ion is formed when an atom gains or loses electrons, resulting in a net positive or negative charge. In this case, an oxygen atom with more electrons than the usual number is referred to as an oxygen ion. Isotopes, on the other hand, are atoms of the same element with different numbers of neutrons. Therefore, an atom of oxygen having more electrons than a neutral oxygen atom is best described as an ion, not an isotope.
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In a double replacement reaction, which of the following occurs?
- A. Energy in the form of heat or light is not always produced.
- B. The reactants can involve a variety of elements.
- C. A gas, solid precipitate, or compound forms in the exchange of ions.
- D. All of the above.
Correct Answer: C
Rationale: In a double replacement reaction, two compounds exchange ions to form two new compounds. This often results in the formation of a gas, a solid precipitate, or a new compound. Choice A is not always true as energy production can vary in different reactions. Choice B is not a defining characteristic of double replacement reactions, as the reactants can involve a variety of elements. Therefore, the correct answer is C, as it accurately describes a common outcome of double replacement reactions.
What does the term 'atomic number' represent?
- A. Number of neutrons
- B. Number of protons
- C. Number of electrons
- D. Number of isotopes
Correct Answer: B
Rationale: The atomic number represents the number of protons in the nucleus of an atom. This number uniquely identifies an element and determines its placement in the periodic table. The number of neutrons and electrons can vary among different isotopes of an element, but the number of protons remains constant, defining the element's atomic number. Therefore, the correct answer is the number of protons (Choice B).
Arrange the following unknown fluids in the correct order of how they would separate in a beaker, listed from bottom to top, based on the given measurements.
- A. A, B, C
- B. A, C, B
- C. C, A, B
- D. B, A, C
Correct Answer: B
Rationale: To determine the order of separation in a beaker, we need to consider the densities of the fluids. Density (d) = mass (m) / volume (V). Comparing the densities of the fluids, we find: Fluid A: d = 2060g / 2000mL = 1.03 g/mL, Fluid B: d = 672g / 850mL = 0.79 g/mL, Fluid C: d = 990g / 1100mL = 0.90 g/mL. Since fluids separate in a beaker based on their densities (with the highest density sinking to the bottom), the correct order from bottom to top is B (highest density), then C, and finally A (lowest density). Therefore, the correct answer is A,C,B.
What is the term for the number of protons in an atom?
- A. atomic identity
- B. atomic mass
- C. atomic weight
- D. atomic number
Correct Answer: D
Rationale: The term for the number of protons in an atom is the atomic number. The atomic number is a fundamental property of an element, representing the number of protons in an atom's nucleus. It serves as the unique identity of an element and determines its position on the periodic table and its chemical behavior. Atomic mass refers to the average mass of an atom, including protons, neutrons, and electrons, while atomic weight is the average weight of an element considering the abundance of its isotopes. 'Atomic identity' is not a standard term in chemistry to describe the number of protons in an atom, making option D, 'atomic number,' the correct answer.
What characterizes bases or alkaline solutions?
- A. Hydrogen acceptors
- B. Solutions of low pH
- C. Hydrogen donors
- D. Amphoteric
Correct Answer: A
Rationale: Bases or alkaline solutions are characterized by their ability to accept protons (hydrogen ions), making them hydrogen acceptors. When a base reacts with an acid, it accepts protons from the acid, forming water and a salt. This property distinguishes bases from acids, which donate protons. Therefore, the correct choice is A, as bases do not donate protons but instead accept them. This property allows bases to neutralize acids and regulate pH levels in solutions, making them crucial in maintaining the balance of acidity and alkalinity in various chemical systems.