The pH of a 0.54M solution of boric acid (HBO3) is measured to be 4.75. Calculate the acid dissociation constant K of boric acid. Round your answer to 2 significant digits. K = ☐ ? x10 X D

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Chapter14: Acids And Bases
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### Calculating the Acid Dissociation Constant (\(K_a\)) of Boric Acid

The problem provides the following information:
- **Solution concentration**: 0.54 M (Molar)
- **Compound**: Boric acid (\(H_3BO_3\))
- **Measured pH**: 4.75

#### Task:
Calculate the acid dissociation constant (\(K_a\)) of boric acid. Round your answer to two significant digits.

#### Step-by-Step Solution:

1. **Determine the concentration of \(H^+\) ions** using the pH value.
   \[
   [H^+] = 10^{-\text{pH}} = 10^{-4.75}
   \]

2. **Express the concentration in scientific notation**.
   \[
   [H^+] \approx 1.78 \times 10^{-5} \, \text{M}
   \]

3. **Set up the expression for \(K_a\)**:
   For a weak acid \(HA\) dissociating into \(H^+\) and \(A^-\):
   \[
   K_a = \frac{[H^+][A^-]}{[HA]}
   \]
   Given that the concentration of \(H^+\) is equal to the concentration of \(A^-\) at equilibrium and the initial concentration of \(HA\) is reduced by the concentration of \(H^+\):
   \[
   \left[H_3BO_3\right] \approx [HA] = 0.54 \, \text{M} - [H^+] \approx 0.54 \, \text{M}
   \]

4. **Simplify the \(K_a\) expression**:
   \[
   K_a = \frac{(1.78 \times 10^{-5})^2}{0.54} = \frac{3.17 \times 10^{-10}}{0.54} \approx 5.87 \times 10^{-10}
   \]

### Completion:
After rounding to two significant digits, the acid dissociation constant \(K_a\) of boric acid is:
\[ K_a \approx 5.9 \times 10^{-10} \]

Here you should input the value for \(K_a\) as: 

\[ K_a = 5.
Transcribed Image Text:### Calculating the Acid Dissociation Constant (\(K_a\)) of Boric Acid The problem provides the following information: - **Solution concentration**: 0.54 M (Molar) - **Compound**: Boric acid (\(H_3BO_3\)) - **Measured pH**: 4.75 #### Task: Calculate the acid dissociation constant (\(K_a\)) of boric acid. Round your answer to two significant digits. #### Step-by-Step Solution: 1. **Determine the concentration of \(H^+\) ions** using the pH value. \[ [H^+] = 10^{-\text{pH}} = 10^{-4.75} \] 2. **Express the concentration in scientific notation**. \[ [H^+] \approx 1.78 \times 10^{-5} \, \text{M} \] 3. **Set up the expression for \(K_a\)**: For a weak acid \(HA\) dissociating into \(H^+\) and \(A^-\): \[ K_a = \frac{[H^+][A^-]}{[HA]} \] Given that the concentration of \(H^+\) is equal to the concentration of \(A^-\) at equilibrium and the initial concentration of \(HA\) is reduced by the concentration of \(H^+\): \[ \left[H_3BO_3\right] \approx [HA] = 0.54 \, \text{M} - [H^+] \approx 0.54 \, \text{M} \] 4. **Simplify the \(K_a\) expression**: \[ K_a = \frac{(1.78 \times 10^{-5})^2}{0.54} = \frac{3.17 \times 10^{-10}}{0.54} \approx 5.87 \times 10^{-10} \] ### Completion: After rounding to two significant digits, the acid dissociation constant \(K_a\) of boric acid is: \[ K_a \approx 5.9 \times 10^{-10} \] Here you should input the value for \(K_a\) as: \[ K_a = 5.
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