Nokea
How many moles of water are produced when 0.5 moles of methane (CH4) react with excess oxygen?
- A. 0.5 moles
- B. 1 mole
- C. 2 moles
- D. 3 moles
Correct Answer: B
Rationale: The balanced chemical equation for the combustion of methane is: CH4 + 2O2 -> CO2 + 2H2O. This equation shows that 1 mole of methane produces 2 moles of water. Therefore, when 0.5 moles of methane react, they will produce 1 mole of water. The ratio of water to methane is 2:1, meaning that for every mole of methane that reacts, it produces 2 moles of water. Since only 0.5 moles of methane are reacting, the amount of water produced will be half of what would be produced if 1 mole of methane reacted, resulting in 1 mole of water being produced. Choice A is incorrect because it does not consider the stoichiometry of the reaction. Choices C and D are incorrect as they do not align with the balanced chemical equation and the stoichiometric ratios involved in the reaction.
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Which of the following is an example of a nonpolar solvent?
- A. Water
- B. Ethanol
- C. Acetone
- D. Hydrochloric acid
Correct Answer: B
Rationale: - Water (option A) is a polar solvent due to its uneven distribution of charge, with the oxygen atom being partially negative and the hydrogen atoms being partially positive.
- Ethanol (option B) is a nonpolar solvent because it has a symmetrical molecular structure that does not result in significant charge separation.
- Acetone (option C) is a polar solvent as it contains a carbonyl group that results in a partial negative charge on the oxygen atom.
- Hydrochloric acid (option D) is a polar solvent due to the presence of the highly electronegative chlorine atom, which results in a partial negative charge.
Where is the thymus gland, crucial for immune system development, located?
- A. Chest
- B. Abdomen
- C. Pelvis
- D. Head and neck
Correct Answer: A
Rationale: The thymus gland is located in the chest, specifically in the upper part of the chest behind the breastbone (sternum). It plays a crucial role in the development and maturation of T-lymphocytes (T cells), which are important for the immune system's function. Choice B (Abdomen), C (Pelvis), and D (Head and neck) are incorrect locations for the thymus gland. The thymus is not found in the abdomen, pelvis, head, or neck regions; it is uniquely situated in the upper chest area.
What information can be obtained from the mass number of an element?
- A. The number of protons in the nucleus
- B. The total number of protons and neutrons
- C. The number of electrons in the valence shell
- D. The element's chemical reactivity
Correct Answer: B
Rationale: The mass number of an element represents the total number of protons and neutrons in the nucleus. This information is crucial for determining the atomic mass of the element and understanding its stability and isotopes. The number of protons in the nucleus (option A) is represented by the atomic number, not the mass number. The number of electrons in the valence shell (option C) is related to the element's position in the periodic table and its chemical properties, but it is not directly determined by the mass number. The element's chemical reactivity (option D) is influenced by the number and arrangement of electrons in the atom's energy levels, not by the mass number.
Which of the following colligative properties refers to the elevation of the boiling point of a solution?
- A. Freezing point depression
- B. Vapor pressure lowering
- C. Osmotic pressure
- D. Boiling point elevation
Correct Answer: D
Rationale: The correct answer is D, 'Boiling point elevation.' Boiling point elevation is a colligative property that describes the increase in the boiling point of a solvent when a non-volatile solute is added to it. This occurs because the presence of solute particles in the solvent lowers the vapor pressure of the solution, requiring a higher temperature to reach the same vapor pressure as the pure solvent. Choices A, B, and C are incorrect. Freezing point depression refers to the lowering of the freezing point of a solution, vapor pressure lowering is the reduction in vapor pressure due to the presence of solute particles, and osmotic pressure is the pressure required to prevent the flow of solvent molecules across a semipermeable membrane in osmosis.
How many moles of oxygen are required to completely react with 5 moles of propane (C3H8) in the combustion reaction?
- A. 5 moles
- B. 10 moles
- C. 15 moles
- D. 20 moles
Correct Answer: C
Rationale: In the balanced chemical equation for the combustion of propane (C3H8): C3H8 + 5O2 → 3CO2 + 4H2O, 1 mole of propane (C3H8) reacts with 5 moles of oxygen (O2). To determine the moles of oxygen required to react with 5 moles of propane, we use the molar ratio: 5 moles propane x 5 moles oxygen / 1 mole propane = 25 moles oxygen. However, since the question specifically asks for the moles of oxygen needed to react with 5 moles of propane, the correct answer is 15 moles of oxygen. Choice A, 5 moles, is incorrect because this is the amount of propane provided, not the oxygen required. Choice B, 10 moles, is incorrect as it does not correspond to the molar ratio in the balanced equation. Choice D, 20 moles, is incorrect as it is not in line with the stoichiometry of the reaction.