To find the concentration of NaOH in a titration problem involving sulfuric acid (H₂SO₄), you'll typically follow these steps:
1. Write the Balanced Chemical Equation:
First, write the balanced equation for the reaction between sodium hydroxide (NaOH) and sulfuric acid (H₂SO₄):
\[ 2 , \text{NaOH} + \text{H₂SO₄} \rightarrow \text{Na₂SO₄} + 2 , \text{H₂O} \]
This indicates that 2 moles of NaOH react with 1 mole of H₂SO₄.
2. Record Your Data:
Collect the following information from the experiment:
- The volume (in liters) of H₂SO₄ solution used in the titration.
- The concentration (in moles per liter, M) of the H₂SO₄ solution used.
- The volume (in liters) of NaOH solution required to reach the endpoint of the titration.
3. Calculate Moles of H₂SO₄:
Using the concentration and the volume of the H₂SO₄ solution, calculate the moles of H₂SO₄:
\[ \text{Moles of H₂SO₄} = \text{Concentration of H₂SO₄ (M)} \times \text{Volume of H₂SO₄ (L)} \]
4. Use Stoichiometry to Find Moles of NaOH:
From the balanced equation, you know that 2 moles of NaOH react with 1 mole of H₂SO₄. Therefore, you can find the moles of NaOH:
\[ \text{Moles of NaOH} = 2 \times \text{Moles of H₂SO₄} \]
5. Calculate Concentration of NaOH:
Finally, use the volume of NaOH solution used during the titration to find its concentration:
\[ \text{Concentration of NaOH (M)} = \frac{\text{Moles of NaOH}}{\text{Volume of NaOH (L)}} \]
Example Problem:
Given:
- Volume of H₂SO₄ = 0.025 L
- Concentration of H₂SO₄ = 0.1 M
- Volume of NaOH = 0.015 L
Steps:
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Calculate the moles of H₂SO₄:
\[ \text{Moles of H₂SO₄} = 0.1 , \text{M} \times 0.025 , \text{L} = 0.0025 , \text{moles} \]
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Calculate the moles of NaOH:
\[ \text{Moles of NaOH} = 2 \times 0.0025 , \text{moles} = 0.005 , \text{moles} \]
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Calculate the concentration of NaOH:
\[ \text{Concentration of NaOH} = \frac{0.005 , \text{moles}}{0.015 , \text{L}} \approx 0.333 , \text{M} \]
So, the concentration of the NaOH solution is approximately 0.333 M.
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