To analyze the pH and conclusions regarding sodium hydroxide, let's break down the information given.
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Understanding pH and pOH:
- pH is a measure of the hydrogen ion concentration (\( [H^+] \)) in a solution.
- pOH is a measure of the hydroxide ion concentration (\( [OH^-] \)) in a solution.
- pH + pOH = 14 (at 25°C).
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Given Information:
- The pH of the solution is 12.
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Calculation of pOH:
- pOH = 14 - pH = 14 - 12 = 2.
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Calculating the Concentration of OH- ions:
- The concentration of hydroxide ions (\( [OH^-] \)) can be derived from pOH: \[ pOH = -\log[OH^-] \implies [OH^-] = 10^{-pOH} = 10^{-2} = 0.01 \text{ M}. \]
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Conclusion about Sodium Hydroxide:
- Sodium hydroxide (NaOH) is known to be a strong base, meaning it dissociates completely in water to produce hydroxide ions (OH^-).
- Since the solution has a pH of 12, which indicates basicity, and the log concentration of OH^- ions correctly aligns with our calculations, we can conclude that sodium hydroxide is indeed a strong base.
Now, let's evaluate the statements:
A. The negative log of the concentration of OH- ions is 2. Sodium hydroxide is a strong acid.
(Incorrect: The conclusion about sodium hydroxide being a strong acid is false.)
B. The negative log of the concentration of OH- ions is 2. Sodium hydroxide is a strong base.
(Correct: The calculation is correct and it identifies sodium hydroxide as a strong base.)
C. The negative log of the concentration of OH- ions is 12. Sodium hydroxide is a strong base.
(Incorrect: The value for \( pOH \) should be 2, not 12.)
D. The negative log of the concentration of OH- ions is 12. Sodium hydroxide is a strong acid.
(Incorrect: Both the log value and conclusion about strong acid are false.)
Based on the analysis, the correct answer is B: The negative log of the concentration of OH- ions is 2. Sodium hydroxide is a strong base.
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