The addition of solid sodium carbonates to pure water causes

Options

A. An increases in the hydronium ion concentration
B. An increase in pH
C. No change in pH
D. A decreases in the hydroxide ion concentration.

Answer

To solve the question regarding the addition of solid sodium carbonate (Na2CO3) to pure water, we can analyze the process step by step.

### Step-by-Step Solution:

1. **Understanding Sodium Carbonate**: Sodium carbonate is a salt that is known to be basic in nature. When it is added to water, it will undergo a reaction.

2. **Dissolution in Water**: When solid sodium carbonate is added to water, it dissolves and dissociates into its ions:
\[ \text{Na}_2\text{CO}_3 (s) \rightarrow 2 \text{Na}^+ (aq) + \text{CO}_3^{2-} (aq) \]

3. **Reaction of Carbonate Ions**: The carbonate ions (\(\text{CO}_3^{2-}\)) can react with water. This reaction can be represented as:
\[ \text{CO}_3^{2-} (aq) + \text{H}_2\text{O} (l) \rightleftharpoons \text{HCO}_3^{-} (aq) + \text{OH}^- (aq) \]
In this reaction, carbonate ions react with water to produce bicarbonate ions (\(\text{HCO}_3^{-}\)) and hydroxide ions (\(\text{OH}^-\)).

4. **Increase in Hydroxide Ion Concentration**: The formation of hydroxide ions (\(\text{OH}^-\)) in the solution increases the concentration of hydroxide ions in the water.

5. **Effect on pH**: The increase in hydroxide ion concentration leads to an increase in the pH of the solution. Since pH is a measure of the acidity or basicity of a solution, an increase in \(\text{OH}^-\) concentration indicates that the solution is becoming more basic (or alkaline).

6. **Conclusion**: Therefore, the addition of solid sodium carbonate to pure water results in an increase in pH due to the formation of hydroxide ions.

### Final Answer:
The addition of solid sodium carbonate to pure water causes an increase in pH, making the solution alkaline.