Nokea
Which of the following elements does not exist as a diatomic molecule?
- A. boron
- B. fluorine
- C. oxygen
- D. nitrogen
Correct Answer: A
Rationale: The correct answer is boron (A). Diatomic molecules consist of two atoms of the same element bonded together. Boron does not naturally form diatomic molecules in its elemental state. Fluorine (FÄ‚‚), oxygen (OÄ‚‚), and nitrogen (NÄ‚‚) are examples of elements that exist as diatomic molecules in their elemental forms. Boron typically forms covalent bonds with other elements but does not naturally exist as a diatomic molecule.
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In a double replacement reaction, which of the following occurs?
- A. Energy in the form of heat or light is often produced.
- B. The reactants are usually a metal and a nonmetal.
- C. A gas, solid precipitate, or compound forms in the exchange of ions.
- D. All statements are true.
Correct Answer: C
Rationale: In a double replacement reaction, the cations and anions of two compounds switch places to form two new compounds. During this process, a gas, solid precipitate, or compound can be formed as the exchange of ions occurs. This often results in the formation of a new product that is insoluble and forms a solid precipitate, a gas that bubbles out, or a compound that remains in the solution. Therefore, choice C is correct as it accurately describes the typical outcomes of a double replacement reaction.
What are buffers?
- A. Proteins
- B. Solutions that resist changes in pH
- C. Catalysts in a reaction
- D. Inhibitors in a reaction
Correct Answer: B
Rationale: Buffers are solutions that resist changes in pH by neutralizing small amounts of acids or bases that may be added to them. They help maintain a stable pH environment and are commonly used in various biological and chemical processes to prevent drastic changes in acidity or alkalinity. Buffers do not act as catalysts or inhibitors in reactions. Their main purpose is to stabilize pH levels and ensure a relatively constant pH within a system, making them essential in maintaining the proper conditions for many biological reactions and processes.
What is the term for the reactant that is entirely consumed in a reaction?
- A. limiting reactant
- B. reducing agent
- C. reaction intermediate
- D. reagent
Correct Answer: A
Rationale: The term for the reactant that is entirely consumed in a reaction is the limiting reactant. The limiting reactant is crucial in determining the maximum amount of product that can be formed as it is fully consumed in the reaction. The other choices, reducing agent, reaction intermediate, and reagent, do not specifically refer to the reactant that is completely consumed during the reaction process. Identifying the limiting reactant is essential for calculating the theoretical yield of a reaction and understanding the stoichiometry of the reaction.
A flask that weighs 345.8 g is filled with 225 mL of carbon tetrachloride. The weight of the flask and carbon tetrachloride is found to be 703.55 g. From this information, calculate the density of carbon tetrachloride.
- A. 1.59 g/mL
- B. 2.76 g/mL
- C. 1.4 g/mL
- D. None are correct.
Correct Answer: A
Rationale: To find the density of carbon tetrachloride, we need to use the formula Density = Mass / Volume. The mass of carbon tetrachloride can be calculated by subtracting the weight of the empty flask from the weight of the flask filled with carbon tetrachloride: Mass of carbon tetrachloride = 703.55 g - 345.8 g = 357.75 g. Now, we can calculate the density: Density = Mass / Volume = 357.75 g / 225 mL = 1.59 g/mL. Therefore, the correct answer is A, 1.59 g/mL.
What occurs to an atom with a negative charge?
- A. Gained an electron
- B. Lost an electron
- C. Gained a proton
- D. Lost a proton
Correct Answer: A
Rationale: When an atom has a negative charge, it means it has gained an electron. Electrons are negatively charged particles, so when an atom gains an electron, it becomes negatively charged. This process is known as gaining an electron to achieve stability through a full outer electron shell. Atoms gain or lose electrons to attain a stable electron configuration, typically following the octet rule. In this case, gaining an electron is the correct choice as it results in the atom having a negative charge.