Chapter 6: Problem 34

Identify the species which can give both conjugate acid and conjugate base. (a) \(\mathrm{NH}_{4}^{+}\) (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) (c) \(\mathrm{PO}_{4}^{-3}\) (d) \(\mathrm{H}_{3} \mathrm{O}^{+}\)

Short Answer

Expert verified

Answer: (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

Step by step solution

Identify potential conjugate acids and conjugate bases

The given species are as follows: (a) \(\mathrm{NH}_{4}^{+}\) (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) (c) \(\mathrm{PO}_{4}^{3-}\) (d) \(\mathrm{H}_{3} \mathrm{O}^{+}\) Now we will examine each species one by one to see if they can act as both a conjugate acid and a conjugate base.

Analyzing \(\mathrm{NH}_{4}^{+}\)

\(\mathrm{NH}_{4}^{+}\) can donate a proton (H+) to become \(\mathrm{NH}_{3}\), which means it can act as a conjugate acid. However, it cannot accept any more protons as it already carries a positive charge and will become unstable. So, \(\mathrm{NH}_{4}^{+}\) can not act as a conjugate base.

Analyzing \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

\(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) can donate a proton to become \(\mathrm{H}\mathrm{PO}_{4}^{2-}\), which means it can act as a conjugate acid. It can also accept a proton to become \(\mathrm{H}_{3} \mathrm{PO}_{4}\), which means it can act as a conjugate base. Therefore, \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) can act as both a conjugate acid and a conjugate base.

Analyzing \(\mathrm{PO}_{4}^{3-}\)

\(\mathrm{PO}_{4}^{3-}\) can accept a proton to become \(\mathrm{H}\mathrm{PO}_{4}^{2-}\), which means it can act as a conjugate base. However, it cannot donate any more protons as it has none available. Therefore, \(\mathrm{PO}_{4}^{3-}\) can not act as a conjugate acid.

Analyzing \(\mathrm{H}_{3} \mathrm{O}^{+}\)

\(\mathrm{H}_{3} \mathrm{O}^{+}\) can donate a proton to become \(\mathrm{H}_{2} \mathrm{O}\), which means it can act as a conjugate acid. However, it cannot accept any more protons as it already carries a positive charge and will become unstable. So, \(\mathrm{H}_{3} \mathrm{O}^{+}\) can not act as a conjugate base.

Final Answer

From the analysis, only \(\mathrm{H}_{2}\mathrm{PO}_{4}^{-}\) can act as both a conjugate acid and a conjugate base. The correct answer is (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\).

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Identify the species which can give both conjugate acid and conjugate base. (a) \(\mathrm{NH}_{4}^{+}\) (b) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) (c) \(\mathrm{PO}_{4}^{-3}\) (d) \(\mathrm{H}_{3} \mathrm{O}^{+}\)

Short Answer

Step by step solution

Identify potential conjugate acids and conjugate bases

Analyzing \(\mathrm{NH}_{4}^{+}\)

Analyzing \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\)

Analyzing \(\mathrm{PO}_{4}^{3-}\)

Analyzing \(\mathrm{H}_{3} \mathrm{O}^{+}\)

Final Answer

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