- Weigh a 250-300 mg (±1 mg) sample of your unknown. Dissolve it in 10 ml distilled water and transfer it with washings into a 50-ml volumetric flask. Add 25 ml of 0.5 M NaIO4. Fill to 50 ml. Mix. Record the time.
- Prepare a blank: The same as above sans sugar.
- Incubate at 37°C.
- At timed intervals (15 min, 1 hr, 24 hr, 48 hr) remove 1-ml samples from both the experimental and blank, and add to 125-ml flasks containing 5 ml 1N (0.5M) sulfuric acid and 5 ml of 20% KI. A large amount of iodine will form immediately.
- Titrate it immediately with 0.1 N sodium thiosulfate - adding it slowly so that a yellow color persists during the titration. When the solution becomes very pale yellow add starch indicator, and continue titrating until the dark color just disappears. (A total of 12-20 ml of thiosulfate will probably be consumed.)
- Record your pairs of values until two sets are identical indicating that the reaction has reached completion.
- The more periodate consumed, the less iodine will result. Thus the difference in iodine between the experimental and blank is related to the amount of periodate consumed. Use this equation:
- Upon completion of periodate consumption, transfer 5 ml of the periodate reaction mixture and the blank to small beakers and add 1 ml of ethylene glycol to each beaker.
- At room temperature, swirl for 5 minutes as the glycol rids the mix of excess periodate.
- Add one drop of phenolphthalein to each beaker, and titrate with 0.05 N NaOH until a definite pink color appears.
- Record your data!
- The moles of formic acid formed is directly related to the amount of base consumed in the titration.
