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Using your knowledge of what defines an acid and a base, answer the following question about this reaction.

[tex]
HCO _3^{-1}+ HPO _4^{-2} \leftrightarrow CO _3^{-2}+ H _2 PO _4^{-1}
[/tex]

In the reverse reaction, which species is acting as an acid?

a. [tex]HCO _3^{-1}[/tex]
b. [tex]HPO _4^{-2}[/tex]
c. [tex]CO _3^{-2}[/tex]
d. [tex]H _2 PO _4^{-1}[/tex]



Answer :

GinnyAnswer
To determine which species is acting as an acid in the reverse reaction, we need to understand the definitions of acids and bases. According to the Brønsted-Lowry theory:

- Acid: A species that donates a proton (H^+).
- Base: A species that accepts a proton (H^+).

In the given reaction:
[tex]\[ HCO_3^{-} + HPO_4^{2-} \leftrightarrow CO_3^{2-} + H_2PO_4^{-} \][/tex]

We need to examine the reverse reaction:
[tex]\[ CO_3^{2-} + H_2PO_4^{-} \leftrightarrow HCO_3^{-} + HPO_4^{2-} \][/tex]

In this reverse reaction:

1. Identify proton transfer:
- [tex]\( H_2PO_4^{-} \)[/tex] could potentially donate a proton (H^+) to become [tex]\( HPO_4^{2-} \)[/tex].
- [tex]\( CO_3^{2-} \)[/tex] is not likely to donate a proton because it’s already in its basic form and would prefer to accept a proton to become [tex]\( HCO_3^{-} \)[/tex].

2. Determine the acid:
- [tex]\( H_2PO_4^{-} \)[/tex] (dihydrogen phosphate ion) donates a proton and transforms into [tex]\( HPO_4^{2-} \)[/tex] (hydrogen phosphate ion).

Therefore, the species that acts as an acid by donating a proton in the reverse reaction is [tex]\( \mathbf{H_2PO_4^{-}} \)[/tex].

The correct answer is:
d. [tex]\( H_2PO_4^{-} \)[/tex]

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