2. Dr. Dahm has a 0.4 M solution of nitrous acid. If he takes 3 mL of this solution and dilutes it to 100 mL calculate the pH of the new solution. (assume that no dissociation takes place until the new solution is made.) Ka = 4.6´ 10-4 HNO₂(aq) + H₂O(1) NO₂ (aq) H,O*(aq) +

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Chapter17: Spontaneity, Entropy, And Free Energy
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Problem 110CWP
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### Problem Statement

Dr. Dahm has a 0.4 M solution of nitrous acid. If he takes 3 mL of this solution and dilutes it to 100 mL, calculate the pH of the new solution. Assume that no dissociation takes place until the new solution is made. The dissociation constant, \( K_a \), for nitrous acid is \( 4.6 \times 10^{-4} \).

### Chemical Reaction

\[ \text{HNO}_2(aq) + \text{H}_2\text{O}(l) \rightarrow \text{H}_3\text{O}^+(aq) + \text{NO}_2^-(aq) \]

### Explanation

1. **Dilution Calculation:**
   - Initial concentration (\( C_i \)) = 0.4 M
   - Initial volume (\( V_i \)) = 3 mL
   - Final volume (\( V_f \)) = 100 mL

   Use the dilution formula:

   \[
   C_f = \frac{C_i \times V_i}{V_f}
   \]

   Calculate the new concentration (\( C_f \)) after dilution.

2. **pH Calculation:**
   - Use the dissociation constant (\( K_a \)) to find the concentration of \( \text{H}_3\text{O}^+ \).
   - Calculate the pH using:

   \[
   \text{pH} = -\log [\text{H}_3\text{O}^+]
   \]

The task involves using chemical equilibrium concepts to find the pH of the solution after dilution.
Transcribed Image Text:### Problem Statement Dr. Dahm has a 0.4 M solution of nitrous acid. If he takes 3 mL of this solution and dilutes it to 100 mL, calculate the pH of the new solution. Assume that no dissociation takes place until the new solution is made. The dissociation constant, \( K_a \), for nitrous acid is \( 4.6 \times 10^{-4} \). ### Chemical Reaction \[ \text{HNO}_2(aq) + \text{H}_2\text{O}(l) \rightarrow \text{H}_3\text{O}^+(aq) + \text{NO}_2^-(aq) \] ### Explanation 1. **Dilution Calculation:** - Initial concentration (\( C_i \)) = 0.4 M - Initial volume (\( V_i \)) = 3 mL - Final volume (\( V_f \)) = 100 mL Use the dilution formula: \[ C_f = \frac{C_i \times V_i}{V_f} \] Calculate the new concentration (\( C_f \)) after dilution. 2. **pH Calculation:** - Use the dissociation constant (\( K_a \)) to find the concentration of \( \text{H}_3\text{O}^+ \). - Calculate the pH using: \[ \text{pH} = -\log [\text{H}_3\text{O}^+] \] The task involves using chemical equilibrium concepts to find the pH of the solution after dilution.
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