Enough of a monoprotic acid is dissolved in water to produce a 1.77 M solution. The pH of the resulting solution is 2.72. Calculate the K₂ for the acid. K₁ =

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### Question 19 of 45

**Problem:**

Enough of a monoprotic acid is dissolved in water to produce a 1.77 M solution. The pH of the resulting solution is 2.72. Calculate the \(K_a\) for the acid.

**Solution:**

\[ K_a = \boxed{\phantom{answer}} \]

*Explanation:*

Here, we are given:
- The concentration of the monoprotic acid solution: 1.77 M
- The pH of the solution: 2.72

To find the acid dissociation constant (\(K_a\)), follow these steps:

1. Use the pH to determine the concentration of hydrogen ions \([H^+]\):
\[ [H^+] = 10^{-\text{pH}} \]
\[ [H^+] = 10^{-2.72} \]

2. Write the dissociation equation for the monoprotic acid (HA):
\[ HA \rightleftharpoons H^+ + A^- \]

3. Set up the expression for the acid dissociation constant (\(K_a\)):
\[ K_a = \frac{[H^+][A^-]}{[HA]} \]
  
Since the acid is monoprotic, \([H^+] = [A^-]\).

4. Calculate \([H^+]\) using the given pH:
\[ [H^+] = 10^{-2.72} \approx 1.91 \times 10^{-3} \text{ M} \]

5. Knowing that \([A^-] = [H^+] = 1.91 \times 10^{-3} \text{ M}\) and the initial concentration of acid is 1.77 M, the concentration of un-dissociated acid \([HA]\) is:
\[ [HA] = 1.77 \text{ M} - 1.91 \times 10^{-3} \text{ M} \]

6. Plug these values into the \(K_a\) expression and solve for \(K_a\):
\[ K_a = \frac{(1.91 \times 10^{-3}) (1.91 \times 10^{-3})}{1.77 - 1.91 \times 10^{-3}} \]
\[ K_a \approx \frac{3.65 \times 10
Transcribed Image Text:### Question 19 of 45 **Problem:** Enough of a monoprotic acid is dissolved in water to produce a 1.77 M solution. The pH of the resulting solution is 2.72. Calculate the \(K_a\) for the acid. **Solution:** \[ K_a = \boxed{\phantom{answer}} \] *Explanation:* Here, we are given: - The concentration of the monoprotic acid solution: 1.77 M - The pH of the solution: 2.72 To find the acid dissociation constant (\(K_a\)), follow these steps: 1. Use the pH to determine the concentration of hydrogen ions \([H^+]\): \[ [H^+] = 10^{-\text{pH}} \] \[ [H^+] = 10^{-2.72} \] 2. Write the dissociation equation for the monoprotic acid (HA): \[ HA \rightleftharpoons H^+ + A^- \] 3. Set up the expression for the acid dissociation constant (\(K_a\)): \[ K_a = \frac{[H^+][A^-]}{[HA]} \] Since the acid is monoprotic, \([H^+] = [A^-]\). 4. Calculate \([H^+]\) using the given pH: \[ [H^+] = 10^{-2.72} \approx 1.91 \times 10^{-3} \text{ M} \] 5. Knowing that \([A^-] = [H^+] = 1.91 \times 10^{-3} \text{ M}\) and the initial concentration of acid is 1.77 M, the concentration of un-dissociated acid \([HA]\) is: \[ [HA] = 1.77 \text{ M} - 1.91 \times 10^{-3} \text{ M} \] 6. Plug these values into the \(K_a\) expression and solve for \(K_a\): \[ K_a = \frac{(1.91 \times 10^{-3}) (1.91 \times 10^{-3})}{1.77 - 1.91 \times 10^{-3}} \] \[ K_a \approx \frac{3.65 \times 10
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