Multiple Choice
What does the very small value of the ionization constant of water, k_w, indicate about the autoionization of water?
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17. Acid and Base Equilibrium
Auto-Ionization
Multiple Choice
Which of the following correctly represents the autoionization reaction for water?
A
H_2O(l) ightarrow H^+(aq) + OH^-(aq)
B
2 H_2O(l) ightarrow H_3O^+(aq) + OH^-(aq)
C
2 H_2O(l) ightarrow 2 H^+(aq) + 2 OH^-(aq)
D
H_2O(l) + OH^-(aq) ightarrow H_3O^+(aq)
Verified step by step guidance1
Understand that the autoionization of water involves two water molecules interacting, where one acts as an acid (proton donor) and the other as a base (proton acceptor).
Write the general form of the autoionization reaction: one water molecule donates a proton (H\^+) to another water molecule, forming hydronium (H\_3O\^+) and hydroxide (OH\^-) ions.
Express this reaction as: \(2\ H\_2O(l) \rightarrow H\_3O\^+(aq) + OH\^-(aq)\), which correctly shows the proton transfer and the species formed.
Recognize that the reaction \(H\_2O(l) \rightarrow H\^+(aq) + OH\^-(aq)\) is incomplete because free protons (H\^+) do not exist alone in aqueous solution; they are always associated with water molecules as hydronium ions.
Eliminate options that show incorrect stoichiometry or species, such as those with 2 H\^+ or involving hydroxide as a reactant, since autoionization is a self-ionization process of pure water.
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