Multiple Choice
On the pH scale, pH is a measure of the concentration of which species in an aqueous solution?
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17. Acid and Base Equilibrium
The pH Scale
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On the pH scale, what does a solution with indicate at ?
A
The solution is strongly acidic, with .
B
The solution is basic, with .
C
The solution is neutral, with .
D
The solution is acidic, with .
Verified step by step guidance1
Recall that pH is defined as \(\mathrm{pH} = -\log{[\mathrm{H}^+]}\), where \([\mathrm{H}^+]\) is the concentration of hydrogen ions in the solution.
At 25°C, pure water autoionizes to produce equal concentrations of hydrogen ions and hydroxide ions, each at \$1 \times 10^{-7}$ M, resulting in a neutral solution.
A pH of 7 corresponds to \([\mathrm{H}^+] = 1 \times 10^{-7}\) M, which matches the concentration of \([\mathrm{OH}^-]\) in pure water at 25°C.
Since \([\mathrm{H}^+] = [\mathrm{OH}^-]\), the solution is neither acidic nor basic but neutral.
Therefore, a solution with pH = 7 at 25°C indicates neutrality, meaning \([\mathrm{H}^+] = [\mathrm{OH}^-]\).
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