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Multiple Choice
On the pH scale for aqueous solutions, what is the smallest possible pH value (theoretical, not limited by practical measurement)?
A
B
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D
There is no fixed minimum; pH can be less than for sufficiently concentrated acids.
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Verified step by step guidance
1
Recall that pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration: \(\mathrm{pH} = -\log_{10}[\mathrm{H}^+]\).
Understand that the pH scale is commonly taught as ranging from 0 to 14, but this range is based on typical concentrations of hydrogen ions in dilute aqueous solutions.
Recognize that if the hydrogen ion concentration \([\mathrm{H}^+]\) is greater than 1 M (which can happen in very concentrated acidic solutions), then the pH value becomes negative because \(-\log_{10}[\mathrm{H}^+]\) will be less than zero.
Therefore, theoretically, there is no fixed minimum pH value; the pH can be less than 0 for sufficiently concentrated acids.
Conclude that the smallest possible pH value is not limited to 0, and the pH scale can extend below zero in theory.