if `NaCO_(3)` is added to the solution of `H_(2)CO_(3)`, the of `H_(2)CO_(3)` solution

Options

A. decreases
B. remains constant
C. increases
D. connot be predicted

Answer

To solve the question of how the addition of sodium carbonate (Na2CO3) affects the solution of carbonic acid (H2CO3), we can break it down into steps:

### Step 1: Understand the Components
- Sodium carbonate (Na2CO3) is a salt that can dissociate in water to form sodium ions (Na+) and carbonate ions (CO3^2-).
- Carbonic acid (H2CO3) is a weak acid that can dissociate into bicarbonate (HCO3^-) and hydrogen ions (H+).

### Step 2: Write the Reaction
When Na2CO3 is added to the solution of H2CO3, the carbonate ions (CO3^2-) can react with the hydrogen ions (H+) from the carbonic acid:
\[ \text{H}_2\text{CO}_3 \rightleftharpoons \text{H}^+ + \text{HCO}_3^- \]
The carbonate ions can react with the hydrogen ions to form bicarbonate:
\[ \text{CO}_3^{2-} + 2\text{H}^+ \rightarrow \text{H}_2\text{CO}_3 \]

### Step 3: Analyze the Effect on H2CO3 Concentration
- When Na2CO3 is added, it provides additional carbonate ions (CO3^2-), which will react with the hydrogen ions (H+) from H2CO3.
- This reaction effectively reduces the concentration of free hydrogen ions in the solution, which shifts the equilibrium of the dissociation of H2CO3 to the left (according to Le Chatelier's principle).
- As a result, the concentration of H2CO3 will **decrease** because more of it is being converted back from bicarbonate and hydrogen ions.

### Conclusion
Thus, when Na2CO3 is added to the solution of H2CO3, the concentration of H2CO3 will **decrease**.