Multiple Choice
At 60°C, the ion product constant of water, Kw, is 9.61 x 10^-14. What is the pH of pure water at this temperature?
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17. Acid and Base Equilibrium
Auto-Ionization
Multiple Choice
What does the very small value of the ionization constant of water, k_w, indicate about the autoionization of water?
A
Autoionization of water does not occur at all under normal conditions.
B
Autoionization of water occurs rapidly and results in a high concentration of H_3O^+ and OH^- ions.
C
Autoionization of water is a rare event and only a small fraction of water molecules ionize at any given time.
D
Autoionization of water is a highly favorable process and most water molecules are ionized.
Verified step by step guidance1
Understand that the ionization constant of water, \(K_w\), represents the equilibrium constant for the autoionization reaction of water: \(\mathrm{2\ H_2O \rightleftharpoons H_3O^+ + OH^-}\).
Recognize that a very small value of \(K_w\) means the equilibrium lies far to the left, favoring the reactants (water molecules) rather than the products (hydronium and hydroxide ions).
Interpret this small \(K_w\) value as indicating that only a tiny fraction of water molecules ionize at any given time, so the concentration of \(\mathrm{H_3O^+}\) and \(\mathrm{OH^-}\) ions is very low.
Conclude that the autoionization of water is a rare event under normal conditions, not a rapid or highly favorable process.
Therefore, the small \(K_w\) value reflects the fact that most water molecules remain in their molecular form, with only a small percentage existing as ions.
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