Nokea
Which substance forms hydroxide ions when placed in water?
- A. Lemon juice
- B. Battery acid
- C. Vinegar
- D. Lye
Correct Answer: D
Rationale: The correct answer is D, lye. Lye, also known as sodium hydroxide (NaOH), is a strong base that forms hydroxide ions (OH-) when placed in water. When lye dissolves in water, it dissociates into sodium ions (Na+) and hydroxide ions, making it an alkaline substance. Lemon juice, battery acid, and vinegar do not form hydroxide ions when placed in water. Lemon juice contains citric acid, battery acid contains sulfuric acid, and vinegar contains acetic acid, none of which produce hydroxide ions when dissolved in water.
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Why does the diffusion rate increase as a substance is heated?
- A. The kinetic energy of particles increases.
- B. The space between particles increases.
- C. The density of particles decreases.
- D. The size of particles increases.
Correct Answer: A
Rationale: The correct answer is A. When a substance is heated, the kinetic energy of particles increases, causing them to move faster. This increased movement allows the particles to spread out more rapidly, leading to a higher diffusion rate. Choice B is incorrect because heating does not directly affect the space between particles. Choice C is incorrect because heating does not necessarily lead to a decrease in the density of particles. Choice D is incorrect because the size of particles does not necessarily increase when a substance is heated. Therefore, the correct explanation for the increase in diffusion rate is the rise in kinetic energy of particles.
Which of the following represents a hydride ion?
- A. Hâ»
- B. Hâº
- C. OHâ»
- D. HCl
Correct Answer: A
Rationale: The hydride ion is denoted by Hâ», indicating that it has gained an extra electron to complete its valence shell, resulting in a full octet and a net charge of -1. This ion is commonly found in metal hydrides and plays a significant role in various chemical reactions. Option B, Hâº, represents a proton with a positive charge. Option C, OHâ», represents the hydroxide ion, consisting of oxygen and hydrogen. Option D, HCl, is a compound composed of hydrogen and chlorine ions, not a hydride ion.
What is the charge of a beta particle?
- A. -1
- B. +1
- C. +2
- D. No charge
Correct Answer: A
Rationale: A beta particle has a charge of -1. Beta particles are high-energy, high-speed electrons emitted during radioactive decay processes. Since electrons carry a charge of -1, beta particles also carry a charge of -1. This negative charge indicates that beta particles are negatively charged. Option B is incorrect as it suggests a positive charge, which is not the case for beta particles. Option C is incorrect as it indicates a higher positive charge, which is not true for beta particles. Option D is incorrect as beta particles do have a charge, which is negative.
Which one does not name a polar molecule?
- A. NH₃
- B. Hâ‚‚S
- C. SOâ‚‚
- D. COâ‚‚
Correct Answer: A
Rationale: The correct answer is NH₃. The molecule NH₃ does not represent a polar molecule because nitrogen and hydrogen in this molecule have a small difference in electronegativity that does not result in a significant polar covalent bond. In contrast, molecules H₂S, SO₂, and CO₂ have polar covalent bonds due to larger electronegativity differences, making them polar molecules. Therefore, options B, C, and D are polar molecules, unlike option A.
What happens in a single displacement reaction?
- A. A compound decomposes into two substances.
- B. An active element displaces a less active element.
- C. A precipitate solid forms from the reaction of two solutions.
- D. The oxidation states of atoms in the reactants change.
Correct Answer: B
Rationale: In a single displacement reaction, an active element displaces a less active element in a compound. This process involves one element replacing another in a compound, resulting in the formation of a new compound. Option A is incorrect because a single displacement reaction does not involve the decomposition of a compound into two substances. Option C is incorrect because it describes a precipitation reaction, not a single displacement reaction. Option D is incorrect because it describes oxidation-reduction reactions, not specifically single displacement reactions.