Multiple Choice
On the pH scale, pH is a measure of what quantity in an aqueous solution?
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17. Acid and Base Equilibrium
The pH Scale
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At , what is the pH of pure distilled water?
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Verified step by step guidance1
Recall that pure distilled water undergoes autoionization, producing equal concentrations of hydrogen ions (H\_3O\^+) and hydroxide ions (OH\^-) at 25\degree C.
The ion product constant for water (K\_w) at 25\degree C is given by the equation: \(K\_w = [\mathrm{H_3O^+}][\mathrm{OH^-}] = 1.0 \times 10^{-14}\).
Since the concentrations of H\_3O\^+ and OH\^- are equal in pure water, let \([\mathrm{H_3O^+}] = [\mathrm{OH^-}] = x\). Then, \(x^2 = 1.0 \times 10^{-14}\).
Solve for \(x\) by taking the square root: \(x = \sqrt{1.0 \times 10^{-14}}\) which gives the concentration of H\_3O\^+ ions in pure water.
Calculate the pH using the formula: \(\mathrm{pH} = -\log[\mathrm{H_3O^+}] = -\log x\). This will give the pH of pure distilled water at 25\degree C.
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