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 first need to understand the definitions of Brønsted acids and bases:

1. **Brønsted Acid**: A substance that can donate a proton (H⁺).
2. **Brønsted Base**: A substance that can accept a proton (H⁺).

Now, let's analyze each option step by step.

### Step 1: Analyze HCO₃⁻ (Bicarbonate Ion)
- **As a Brønsted Acid**: HCO₃⁻ can donate a proton (H⁺) to form CO₃²⁻ (carbonate ion).
- Reaction: HCO₃⁻ → CO₃²⁻ + H⁺
- **As a Brønsted Base**: HCO₃⁻ can accept a proton (H⁺) to form H₂CO₃ (carbonic acid).
- Reaction: HCO₃⁻ + H⁺ → H₂CO₃

**Conclusion**: HCO₃⁻ can act as both a Brønsted acid and a Brønsted base.

### Step 2: Analyze K₂CO₃ (Potassium Carbonate)
- **As a Brønsted Acid**: K₂CO₃ does not have any hydrogen atoms that can be donated as protons.
- **As a Brønsted Base**: K₂CO₃ can accept protons to form HCO₃⁻.
- Reaction: K₂CO₃ + H⁺ → 2K⁺ + HCO₃⁻

**Conclusion**: K₂CO₃ can only act as a Brønsted base, not an acid.

### Step 3: Analyze H₂SO₄ (Sulfuric Acid)
- **As a Brønsted Acid**: H₂SO₄ can donate a proton (H⁺) to form HSO₄⁻ (hydrogen sulfate ion).
- Reaction: H₂SO₄ → HSO₄⁻ + H⁺
- **As a Brønsted Base**: H₂SO₄ cannot accept a proton because it does not have any sites available for protonation.

**Conclusion**: H₂SO₄ can only act as a Brønsted acid, not a base.

### Step 4: Analyze H₂PO₄⁻ (Dihydrogen Phosphate Ion)
- **As a Brønsted Acid**: H₂PO₄⁻ can donate a proton (H⁺) to form HPO₄²⁻ (hydrogen phosphate ion).
- Reaction: H₂PO₄⁻ → HPO₄²⁻ + H⁺
- **As a Brønsted Base**: H₂PO₄⁻ can accept a proton (H⁺) to form H₃PO₄ (phosphoric acid).
- Reaction: H₂PO₄⁻ + H⁺ → H₃PO₄

**Conclusion**: H₂PO₄⁻ can act as both a Brønsted acid and a Brønsted base.

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