Which of the following compounds/ions can act as bronsted acid as well as a bronsted base?

Options

A. `HCO_(3)^(-)`
B. `K_(2)CO_(3)`
C. `H_(2)SO_(4)`
D. `H_(2)PO_(4)^(-)`

Answer

To determine which of the given compounds or ions can act as both a Brønsted acid and a Brønsted base, we need to analyze each option based on their ability to donate and accept protons (H⁺ ions).

### Step-by-Step Solution:

1. **Understanding Brønsted Acids and Bases**:
- A Brønsted acid is a substance that donates a proton (H⁺).
- A Brønsted base is a substance that accepts a proton (H⁺).

2. **Analyzing Each Compound/Ion**:
- **Option 1: HCO₃⁻ (Bicarbonate Ion)**:
- **As a Brønsted base**: It can accept a proton to form H₂CO₃ (carbonic acid).
\[ \text{HCO}_3^- + \text{H}^+ \rightarrow \text{H}_2\text{CO}_3 \]
- **As a Brønsted acid**: It can donate a proton to form CO₃²⁻ (carbonate ion).
\[ \text{HCO}_3^- \rightarrow \text{CO}_3^{2-} + \text{H}^+ \]
- **Conclusion**: HCO₃⁻ can act as both a Brønsted acid and a Brønsted base.

- **Option 2: K₂CO₃ (Potassium Carbonate)**:
- **As a Brønsted base**: It can accept a proton to form KHCO₃ (potassium bicarbonate).
\[ \text{K}_2\text{CO}_3 + \text{H}^+ \rightarrow \text{KHCO}_3 + \text{K}^+ \]
- **As a Brønsted acid**: It does not have any protons to donate.
- **Conclusion**: K₂CO₃ cannot act as a Brønsted acid.

- **Option 3: H₂SO₄ (Sulfuric Acid)**:
- **As a Brønsted acid**: It can donate a proton to form HSO₄⁻ (hydrogen sulfate).
\[ \text{H}_2\text{SO}_4 \rightarrow \text{HSO}_4^- + \text{H}^+ \]
- **As a Brønsted base**: It cannot accept a proton as it does not have any basic sites.
- **Conclusion**: H₂SO₄ cannot act as a Brønsted base.

- **Option 4: H₂PO₄⁻ (Dihydrogen Phosphate Ion)**:
- **As a Brønsted base**: It can accept a proton to form H₃PO₄ (phosphoric acid).
\[ \text{H}_2\text{PO}_4^- + \text{H}^+ \rightarrow \text{H}_3\text{PO}_4 \]
- **As a Brønsted acid**: It can donate a proton to form HPO₄²⁻ (hydrogen phosphate).
\[ \text{H}_2\text{PO}_4^- \rightarrow \text{HPO}_4^{2-} + \text{H}^+ \]
- **Conclusion**: H₂PO₄⁻ can act as both a Brønsted acid and a Brønsted base.

3. **Final Answer**:
- The compounds that can act as both Brønsted acids and Brønsted bases are:
- **HCO₃⁻ (Bicarbonate Ion)**
- **H₂PO₄⁻ (Dihydrogen Phosphate Ion)**

### Summary of Results:
- **Correct Options**: HCO₃⁻ and H₂PO₄⁻