Nokea
Which of the following statements is most accurate about chemical formulas?
- A. 2Hâ‚‚O has a total of 2 hydrogen atoms
- B. 2Hâ‚‚O represents two water molecules
- C. Hâ‚‚Oâ‚‚ represents two water molecules
- D. None of the above
Correct Answer: B
Rationale: The correct answer is 'B: 2Hâ‚‚O represents two water molecules.' The chemical formula for water is Hâ‚‚O, which consists of two hydrogen atoms and one oxygen atom per molecule. Therefore, when it is written as 2Hâ‚‚O, it indicates two water molecules. Option B accurately represents this, making it the most accurate statement among the choices.
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Which of the following describes atomic mass?
- A. Mass of protons and electrons
- B. Mass of neutrons and electrons
- C. Average mass of that element's isotopes
- D. Number of moles in a solution
Correct Answer: C
Rationale: The correct answer is C: Average mass of that element's isotopes. Atomic mass is the weighted average mass of the isotopes of an element, considering the natural abundance of each isotope. It is not just the sum of protons and neutrons or neutrons and electrons. Understanding atomic mass is crucial in chemistry as it helps in determining the molar mass of elements, which is essential in various chemical calculations such as stoichiometry and reaction equations.
What is 119 K in degrees Celsius?
- A. 32C
- B. -154C
- C. 154C
- D. -32C
Correct Answer: B
Rationale: To convert from Kelvin to Celsius, you subtract 273.15 from the temperature in Kelvin. Therefore, 119 K - 273.15 = -154C. Hence, 119 K is equivalent to -154C. The correct answer is -154C, as it results from the conversion formula from Kelvin to Celsius.
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.
At very high temperatures, which state of matter is most commonly present?
- A. Solid
- B. Liquid
- C. Gas
- D. None of the above
Correct Answer: C
Rationale: At very high temperatures, substances tend to exist in the gaseous state. This is because the high energy levels cause the particles to move more rapidly and break free from the solid or liquid state. The increased movement and energy lead to gases being commonly present at very high temperatures. Therefore, the correct answer is 'Gas.'
What is the pH of a solution with a pH of 7?
- A. Acidic
- B. Basic
- C. Neutral
- D. Positive
Correct Answer: C
Rationale: The correct answer is C: Neutral. A pH of 7 is considered neutral on the pH scale, which ranges from 0 to 14. A pH of 7 indicates a balance between acidic and basic properties in a solution, making it neither acidic nor basic. Values below 7 are acidic, above 7 are basic, and 7 is the midpoint representing neutrality. Therefore, a solution with a pH of 7 is neutral.