Multiple Choice
Hair, skin, and nails are generally considered to be slightly acidic. Which pH range best describes their typical surface pH?
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17. Acid and Base Equilibrium
The pH Scale
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Which statement best describes an alkaline (basic) aqueous solution at 25 °C?
A
It has and .
B
It has and .
C
It has and .
D
It has and .
Verified step by step guidance1
Recall that pH is a measure of the hydrogen ion concentration in an aqueous solution, defined as \(\mathrm{pH} = -\log[\mathrm{H}^+]\).
Understand that at 25 °C, pure water is neutral with \(\mathrm{pH} = 7\), where the concentration of hydrogen ions \([\mathrm{H}^+]\) equals the concentration of hydroxide ions \([\mathrm{OH}^-]\).
Recognize that an alkaline (basic) solution has a pH greater than 7, which means the concentration of hydroxide ions \([\mathrm{OH}^-]\) is greater than the concentration of hydrogen ions \([\mathrm{H}^+]\).
Use the relationship between \([\mathrm{H}^+]\) and \([\mathrm{OH}^-]\) in water at 25 °C, given by the ion product constant of water: \(K_w = [\mathrm{H}^+][\mathrm{OH}^-] = 1.0 \times 10^{-14}\).
Conclude that for a basic solution, since \(\mathrm{pH} > 7\), it follows that \([\mathrm{OH}^-] > [\mathrm{H}^+]\), which best describes an alkaline aqueous solution at 25 °C.
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