Titrage colorimétrique (dosage) | 1ère spé | Chimie
Table of Contents
Introduction
This tutorial provides a comprehensive guide on colorimetric titration, a key technique in chemistry for determining the concentration of a solution. By following these steps, you will learn how to perform a colorimetric titration, recognize the equivalence point, and calculate the concentration of the titrated solution.
Step 1: Understanding Titration
- Titration is a quantitative analytical method used to determine the concentration of a solute in a solution.
- It involves adding a titrant (a solution of known concentration) to a titrand (the solution of unknown concentration) until the reaction reaches its equivalence point.
- The equivalence point is where the amount of titrant added reacts completely with the titrand.
Practical Tips
- Ensure all glassware is clean to avoid contamination.
- Prepare a proper workspace with all materials at hand, including the titrant and the solution to be analyzed.
Step 2: Identifying the Equivalence Point
- The equivalence point can often be identified using an indicator that changes color at a specific pH.
- In colorimetric titration, the color change is monitored visually to determine when the titration is complete.
Common Pitfalls
- Adding too much titrant can lead to overshooting the equivalence point.
- Be cautious with the choice of indicator; it should be suitable for the specific reaction and pH range.
Step 3: Performing Colorimetric Titration
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Set Up Your Apparatus
- Use a burette to dispense the titrant.
- Place the titrand solution in a flask and add the appropriate indicator.
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Conduct the Titration
- Slowly add the titrant from the burette to the titrand while swirling the flask.
- Observe the color change closely. Stop adding the titrant once you see a permanent color change.
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Record the Volume of Titrant Used
- Note the initial and final volume readings on the burette to determine the volume of titrant added.
Step 4: Calculating the Concentration of the Titrand
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Use the formula to calculate the concentration of the titrand once you have reached the equivalence point:
[ C_1V_1 = C_2V_2 ]
Where:
- (C_1) = concentration of the titrant
- (V_1) = volume of the titrant used
- (C_2) = concentration of the titrand (unknown)
- (V_2) = volume of the titrand
Example Calculation
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If you used 0.1 M NaOH as the titrant and added 25 mL to 50 mL of an unknown HCl solution, you would set up the equation:
[ 0.1 \times 25 = C_2 \times 50 ]
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Solving for (C_2) gives you the concentration of the HCl solution.
Conclusion
Colorimetric titration is an essential technique for determining the concentration of unknown solutions. By following the outlined steps, you can successfully conduct a titration, identify the equivalence point, and calculate the concentration of the titrand. Remember to practice careful measurement and observation to ensure accurate results. For further study, consider exploring different indicators and their suitability for various titrations.