If `Na_2 CO_3` is added to the solution of `H_3 CO_3` the pH of `H_2 CO_3` solution

Options

A. decreases
B. increases
C. remains constant
D. cannot be predicted

Answer

To determine how the pH of a solution of carbonic acid (H₂CO₃) is affected when sodium carbonate (Na₂CO₃) is added, we can follow these steps:

### Step 1: Understand the Components
- Sodium carbonate (Na₂CO₃) is a salt that, when dissolved in water, dissociates into sodium ions (Na⁺) and carbonate ions (CO₃²⁻).
- Carbonic acid (H₂CO₃) is a weak acid.

**Hint:** Remember that salts can affect the pH of a solution based on their acidic or basic nature.

### Step 2: Analyze the Reaction
- When Na₂CO₃ is added to the H₂CO₃ solution, the carbonate ions (CO₃²⁻) can react with the hydrogen ions (H⁺) present in the solution.
- The reaction can be represented as:
\[ CO₃^{2-} + H⁺ \rightarrow HCO₃^{-} \]
- This reaction decreases the concentration of H⁺ ions in the solution.

**Hint:** Look for how the addition of a salt can interact with the existing acid in the solution.

### Step 3: Effect on H⁺ and OH⁻ Concentration
- As the concentration of H⁺ ions decreases due to the reaction with CO₃²⁻, the concentration of hydroxide ions (OH⁻) effectively increases.
- The pH of a solution is determined by the concentration of H⁺ ions; a decrease in H⁺ concentration leads to an increase in pH.

**Hint:** Recall that pH is inversely related to H⁺ concentration.

### Step 4: Conclusion on pH Change
- Since the addition of Na₂CO₃ results in a decrease in H⁺ concentration and an increase in OH⁻ concentration, the overall effect is that the solution becomes more basic.
- Therefore, the pH of the H₂CO₃ solution will increase when Na₂CO₃ is added.

**Hint:** Consider how the pH scale works: lower H⁺ concentration means a higher pH value.

### Final Answer
The pH of the H₂CO₃ solution will increase upon the addition of Na₂CO₃.