Describe the procedure you would follow to determine the concentration of Vitamin C in a sample if the volume of DCPIP required to reach the endpoint was more than the 25-mL flask could hold. Note the titration must still be carried out in the flask. Be sure to include any calculations you would need to perform.
I don't know the exact procedure you're using but if the original solution is in a volumetric flask you simply take an aliquot and go from there.
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To determine the concentration of Vitamin C in a sample using DCPIP titration, there are a few steps you can follow if the volume of DCPIP required to reach the endpoint exceeds the capacity of a 25-mL flask. Here's a step-by-step procedure:
1. Prepare a solution of known concentration of Vitamin C. This solution will serve as the standard solution against which the sample will be compared. Dilute the stock Vitamin C solution to achieve a concentration within the expected range of the sample.
2. Set up the titration apparatus. Place the 25-mL flask on a white tile or paper to facilitate color change observation. The titration apparatus consists of a burette filled with the DCPIP solution and a pipette to measure the sample.
3. Pipette a smaller volume of the sample into the flask. Start by measuring a sample volume that can be easily handled by the 25-mL flask, for example, 5 mL.
4. Add a few drops of indicator solution. In this case, DCPIP is used as the indicator. DCPIP is typically blue in its oxidized form and turns colorless when reduced.
5. Start the titration by slowly adding DCPIP from the burette to the sample in the flask, while continuously swirling the flask. The blue color of the DCPIP will begin to fade as it reacts with Vitamin C in the sample.
6. Watch for the color change. The endpoint is reached when the blue color of DCPIP disappears completely, indicating that all the DCPIP has been reduced by the Vitamin C. Record the volume of DCPIP added from the burette.
7. Calculate the concentration of Vitamin C in the sample. Since the volume of DCPIP required to reach the endpoint exceeded the flask's capacity, you'll need to make some calculations to determine the concentration of Vitamin C.
First, calculate the concentration of Vitamin C in the sample using the equation:
Concentration of Vitamin C in sample = (Volume of DCPIP in moles) x (Moles of Vitamin C per mole of DCPIP) / Volume of sample in liters
To calculate the moles of DCPIP used, convert the volume of DCPIP added to liters:
Volume of sample in liters = (Volume of DCPIP added) / 1000
The moles of DCPIP used can be determined using its concentration and the volume added:
Moles of DCPIP used = (Volume of DCPIP added in liters) x (Concentration of DCPIP)
Lastly, use the stoichiometry of DCPIP and Vitamin C to determine the moles of Vitamin C used:
Moles of Vitamin C used = (Moles of DCPIP used) x (Moles of Vitamin C per mole of DCPIP)
With these values, you can calculate the concentration of Vitamin C in the sample.
Remember to repeat the titration at least three times to obtain consistent and accurate results.