Answered

Which of these equations correctly expresses the self-ionization of water?

A. [tex]H_2O + H_2O^+ \leftrightarrow H_2O + OH^-[/tex]

B. [tex]H_2O + H_2O \leftrightarrow 2OH^-[/tex]

C. [tex]H_3O + H_2O \leftrightarrow 2H_3O^\circ[/tex]

D. [tex]H_2O + H_2O \leftrightarrow H_3O^+ + OH^-[/tex]



Answer :

To determine which of these equations correctly expresses the self-ionization of water, let's first understand the process itself.

The self-ionization (or autoionization) of water is the process wherein two water molecules interact to produce a hydronium ion (H[tex]\(_3\)[/tex]O[tex]\(^+\)[/tex]) and a hydroxide ion (OH[tex]\(^-\)[/tex]). The correct representation of this reaction is as follows:

[tex]\[ 2 \text{H}_2\text{O} \leftrightarrow \text{H}_3\text{O}^+ + \text{OH}^- \][/tex]

Now, let's compare each given option to this accurate equation:

1. Option 1:
[tex]\[ \text{H}_2\text{O} + \text{H}_2\text{O}^+ \leftrightarrow \text{H}_2\text{O} + \text{OH}^- \][/tex]
This equation suggests that one water molecule and a water cation (H[tex]\(_2\)[/tex]O[tex]\(^+\)[/tex]) produce a water molecule and a hydroxide ion. This configuration is incorrect because it doesn't represent the formation of both a hydronium and hydroxide ion from two water molecules.

2. Option 2:
[tex]\[ \text{H}_2\text{O} + \text{H}_2\text{O} \leftrightarrow 2 \text{OH}^- \][/tex]
This equation implies that two water molecules produce two hydroxide ions, which is incorrect because it doesn't produce a hydronium ion, which is an essential part of the self-ionization process.

3. Option 3:
[tex]\[ \text{H}_3\text{O} + \text{H}_2\text{O} \leftrightarrow 2 \text{H}_3\text{O}^\circ \][/tex]
This suggests that a hydronium ion and a water molecule produce two hydronium ions, which is incorrect because it lacks the production of a hydroxide ion.

4. Option 4:
[tex]\[ \text{H}_2\text{O} + \text{H}_2\text{O} \leftrightarrow \text{H}_1\text{O}^+ + \text{OH}^- \][/tex]
This equation indicates that two water molecules produce a hypothetical H[tex]\(_1\)[/tex]O[tex]\(^+\)[/tex] (which is not a commonly recognized species in chemistry) and a hydroxide ion. This is certainly incorrect.

Upon evaluating these options, we can see that none of them match the exact form:

[tex]\[ 2 \text{H}_2\text{O} \leftrightarrow \text{H}_3\text{O}^+ + \text{OH}^- \][/tex]

However, if we are to select the closest option based on the concept of ion production, Option 1 at least represents an ion exchange involving water and has some similarity to part of the process even though it is not perfect.

Thus, the answer would be Option 1:

[tex]\[ \boxed{H _2 O + H _2 O ^{+} \leftrightarrow H _2 O + OH ^{-}} \][/tex]