Nokea
Which of the following statements is most accurate regarding the compound 2Hâ‚‚O?
- A. 2Hâ‚‚O has a total of 2 hydrogen atoms.
- B. 2Hâ‚‚O represents two water molecules.
- C. Hâ‚‚O represents two water molecules.
- D. None of the above.
Correct Answer: B
Rationale: The chemical formula 2Hâ‚‚O represents two water molecules. Each water molecule (Hâ‚‚O) consists of 2 hydrogen atoms and 1 oxygen atom. Therefore, 2Hâ‚‚O denotes two separate water molecules, making choice B the correct statement
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What is a combustion reaction?
- A. It is endothermic.
- B. It substitutes one element for another.
- C. It always shares electrons.
- D. It is a reaction that involves oxygen.
Correct Answer: D
Rationale: A combustion reaction is a type of chemical reaction that involves a substance reacting with oxygen gas to produce heat and light. This reaction is exothermic, releasing energy in the form of heat and light. The correct answer is D because combustion reactions specifically involve oxygen as a reactant, leading to the production of heat and light as byproducts.
What does carbonic acid become within the human body?
- A. Digests food
- B. Kills viruses
- C. Maintains pH of blood
- D. Grows hair
Correct Answer: C
Rationale: Carbonic acid, formed when carbon dioxide dissolves in water, plays a crucial role in maintaining the pH balance of the blood. It acts as a buffer to prevent drastic changes in blood pH, which is vital for the body's proper functioning. Carbonic acid does not digest food, kill viruses, or contribute to hair growth. Therefore, options A, B, and D are incorrect roles of carbonic acid within the human body, making maintaining the pH of blood (Option C) the correct answer.
A block on your desk acts as a paperweight with measurements of 3 cm by 4 cm by 6 cm. The block has a mass of 184.32 g. What is its density?
- A. 13,271.04 g/cm³
- B. 2.56 g/cm³
- C. 0.39 g/cm³
- D. None of the above
Correct Answer: B
Rationale: Density is calculated by dividing mass by volume. To find the volume of the block, multiply its dimensions (3 cm x 4 cm x 6 cm = 72 cm³). Dividing the mass (184.32 g) by the volume (72 cm³) gives a density of 2.56 g/cm³. Therefore, the correct answer is B.
What are van der Waals forces?
- A. the weak forces of attraction between two molecules
- B. the strong forces of attraction between two molecules
- C. hydrogen bonds
- D. conjugal bonds
Correct Answer: A
Rationale: Van der Waals forces are weak intermolecular forces that occur between non-polar molecules. These forces result from temporary fluctuations in electron distribution within the molecules, leading to slight positive and negative charges. This results in weak attraction between molecules through van der Waals forces. Hydrogen bonds, in contrast, are stronger intermolecular forces that specifically occur between molecules containing hydrogen bonded to a highly electronegative atom like oxygen or nitrogen. Conjugal bonds do not exist in chemistry and are not relevant to intermolecular forces.
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.