You titrate samples exactly the same as you did your standard. Record the initial and final volume of iodine solution required to produce the color change at the endpoint.
Titrating Juice Samples
- Add 25.00 ml of juice sample to a 125 ml Erlenmeyer flask.
- Titrate until the endpoint is reached. (Add iodine solution until you get a color that persists longer than 20 seconds.)
- Repeat the titration until you have at least three measurement that agree to within 0.1 ml.
Titrating Real Lemon
Real Lemon is nice to use because the maker lists vitamin C, so you can compare your value with the packaged value. You can use another packaged lemon or lime juice, provided the amount of vitamin C is listed on the packaging. Keep in mind, the amount can change (diminish) once the container has been opened or after it has been stored for a long time.
- Add 10.00 ml of Real Lemon into a 125 ml Erlenmeyer flask.
- Titrate until you have at least three measurements that agree within 0.1 ml of iodine solution.
- Vitamin C Tablet - Dissolve the tablet in ~100 ml distilled water. Add distilled water to make 200 ml of solution in a volumetric flask.
- Fresh Fruit Juice - Strain the juice through a coffee filter or cheese cloth to remove pulp and seeds, since they could get stuck in the glassware.
- Packaged Fruit Juice - This also may require straining.
- Fruits & Vegetables - Blend a 100 g sample with ~50 ml of distilled water. Strain the mixture. Wash the filter with a few milliliters of distilled water. Add distilled water to make a final solution of 100 ml in a volumetric flask.