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 follow these steps:

### Step 1: Understand the nature of sodium carbonate
Sodium carbonate (Na2CO3) is a salt formed from a strong base (sodium hydroxide, NaOH) and a weak acid (carbonic acid, H2CO3). This means that it has basic properties when dissolved in water.

**Hint:** Remember that salts derived from strong bases and weak acids tend to be basic in nature.

### Step 2: Dissolution of sodium carbonate in water
When solid sodium carbonate is added to water, it dissolves and dissociates into its constituent ions:
\[ \text{Na}_2\text{CO}_3 \rightarrow 2 \text{Na}^+ + \text{CO}_3^{2-} \]

**Hint:** Focus on the ions produced when sodium carbonate dissolves in water.

### Step 3: Reaction of carbonate ions with water
The carbonate ions (CO3^2-) can react with water (H2O) to produce bicarbonate ions (HCO3^-) and hydroxide ions (OH^-):
\[ \text{CO}_3^{2-} + \text{H}_2\text{O} \rightleftharpoons \text{HCO}_3^- + \text{OH}^- \]

This reaction shows that the carbonate ions increase the concentration of hydroxide ions in the solution.

**Hint:** Consider how the carbonate ions interact with water and what products are formed.

### Step 4: Effect on hydroxide ion concentration
The formation of hydroxide ions (OH^-) from the reaction above leads to an increase in the concentration of hydroxide ions in the solution.

**Hint:** Increasing hydroxide ion concentration indicates a basic solution.

### Step 5: Effect on pH
Since pH is a measure of the hydrogen ion concentration, an increase in hydroxide ions will result in a decrease in hydrogen ion concentration (H3O^+), leading to an increase in pH. Thus, the pH of the solution will rise.

**Hint:** Remember that pH and hydroxide ion concentration are inversely related to hydrogen ion concentration.

### Conclusion
Based on the above reasoning, the addition of solid sodium carbonate to pure water causes an increase in pH.

**Final Answer:** The correct option is B: an increase in pH.