What is the resultant pH after mixing 30.0 mL of 0.50 M HCI with 20.0 mL of 0.90 M NaOH? Express your answer in decimal notation rounded to four significant figures.

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**Problem Statement:**

What is the resultant pH after mixing 30.0 mL of 0.50 M HCl with 20.0 mL of 0.90 M NaOH? Express your answer in decimal notation rounded to four significant figures.

**Solution Explanation:**

To solve this problem, follow these steps:

1. **Calculate the moles of HCl and NaOH:**
   - Moles of HCl = Volume (L) × Concentration (M) = \(0.030 \, \text{L} \times 0.50 \, \text{M} = 0.015 \, \text{moles}\)
   - Moles of NaOH = Volume (L) × Concentration (M) = \(0.020 \, \text{L} \times 0.90 \, \text{M} = 0.018 \, \text{moles}\)

2. **Determine the limiting reactant:**
   - NaOH is in excess since it has 0.018 moles compared to 0.015 moles of HCl.

3. **Calculate the moles of excess NaOH:**
   - Moles of excess NaOH = 0.018 - 0.015 = 0.003 moles

4. **Calculate the concentration of the excess NaOH in the final solution:**
   - Total volume of the solution = 30.0 mL + 20.0 mL = 50.0 mL = 0.050 L
   - Concentration of NaOH = 0.003 moles / 0.050 L = 0.06 M

5. **Calculate the pH of the solution:**
   - pH = 14 - pOH
   - pOH = -log[OH⁻] = -log(0.06)
   - pOH ≈ 1.2218
   - pH = 14 - 1.2218 = 12.7782

Therefore, the resultant pH of the solution is **12.78** when rounded to four significant figures.
Transcribed Image Text:**Problem Statement:** What is the resultant pH after mixing 30.0 mL of 0.50 M HCl with 20.0 mL of 0.90 M NaOH? Express your answer in decimal notation rounded to four significant figures. **Solution Explanation:** To solve this problem, follow these steps: 1. **Calculate the moles of HCl and NaOH:** - Moles of HCl = Volume (L) × Concentration (M) = \(0.030 \, \text{L} \times 0.50 \, \text{M} = 0.015 \, \text{moles}\) - Moles of NaOH = Volume (L) × Concentration (M) = \(0.020 \, \text{L} \times 0.90 \, \text{M} = 0.018 \, \text{moles}\) 2. **Determine the limiting reactant:** - NaOH is in excess since it has 0.018 moles compared to 0.015 moles of HCl. 3. **Calculate the moles of excess NaOH:** - Moles of excess NaOH = 0.018 - 0.015 = 0.003 moles 4. **Calculate the concentration of the excess NaOH in the final solution:** - Total volume of the solution = 30.0 mL + 20.0 mL = 50.0 mL = 0.050 L - Concentration of NaOH = 0.003 moles / 0.050 L = 0.06 M 5. **Calculate the pH of the solution:** - pH = 14 - pOH - pOH = -log[OH⁻] = -log(0.06) - pOH ≈ 1.2218 - pH = 14 - 1.2218 = 12.7782 Therefore, the resultant pH of the solution is **12.78** when rounded to four significant figures.
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