To identify the correct relationship between substances in the given reaction:
[tex]\[
H_2CO_3 + H_2O \rightleftharpoons H_3O^+ + HCO_3^-
\][/tex]
We need to understand the concepts of acids, bases, and their conjugates:
1. Conjugate Acid-Base Pairs: In a chemical reaction, an acid donates a proton (H⁺) and becomes its conjugate base, while a base accepts a proton and becomes its conjugate acid.
Let's analyze the reaction step by step:
- Acids and Bases:
- [tex]\( H_2CO_3 \)[/tex] (carbonic acid) is a weak acid.
- [tex]\( H_2O \)[/tex] (water) acts as a base.
- [tex]\( H_3O^+ \)[/tex] (hydronium ion) is a strong acid.
- [tex]\( HCO_3^- \)[/tex] (bicarbonate) is the conjugate base of [tex]\( H_2CO_3 \)[/tex].
- Proton Transfer:
- [tex]\( H_2CO_3 \)[/tex] loses a proton to become [tex]\( HCO_3^- \)[/tex].
- [tex]\( H_2O \)[/tex] accepts a proton to become [tex]\( H_3O^+ \)[/tex].
From these points, let's examine each statement:
A. [tex]\( HCO_3^- \)[/tex] is the conjugate base of [tex]\( H_2CO_3 \)[/tex], not the conjugate acid. Thus, this statement is incorrect.
B. [tex]\( H_2O \)[/tex] is not the conjugate base of [tex]\( H_2CO_3 \)[/tex]. Instead, it is a base in this reaction. Thus, this statement is incorrect.
C. [tex]\( H_3O^+ \)[/tex] is the conjugate acid of [tex]\( H_2O \)[/tex]. When [tex]\( H_2O \)[/tex] accepts a proton, it becomes [tex]\( H_3O^+ \)[/tex]. This statement is correct.
D. [tex]\( H_2CO_3 \)[/tex] is the acid, not the conjugate base of [tex]\( H_3O^+ \)[/tex]. Thus, this statement is incorrect.
Therefore, the correct answer is:
[tex]\[
\boxed{\text{C. } H_3O^+ \text{ is the conjugate acid of } H_2O.}
\][/tex]
