Shawn910018的部落格

Experiment date: 2013/10/29

1. Principle:

We’ll learn how to use lodine to titration the Vitamin C in juice or Vitamin C

tables. And find out the damage level from air or temperature at the same time. We can also learn the meaning and the way to use acid-base back titration.

1. Chemicals and their Properties:

H₂SO₄ (CAS 7758-01-2):                167.0005 g/mol d:1.84g/cm³ mp: 10 °C

bp: 337 °C

KBrO₃ (CAS 7664-93-9):               148.1 g/mol d: 3.27 g/cm³ mp: 350 °C dp: 370 °C Looks: White powder

Na₂S₂O₃ (CAS 7772-98-7):            158.09774 g/mol d:1.84g/cm³ mp: 48.3 °C

KBr (CAS 7758-02-3):                   119.0023 g/mol d: 2.75g/cm³ mp: 734 °C

bp: 1435 °C

KI (CAS 7681-11-0):                      166.0028 g/mol       d: 3.123 g/cm³ mp: 681 °C bp: 1330 °C

Starch iodide (CAS 9005-25-8):     d: 1.5 g/cm³            Looks: White powder

Vitamin C (CAS 50-81-7):              d: 1.694g/cm³  mp: 190–192 °C bp: 553 °C

1. Tools:

1. Pasteur pipette (10mL)

2. Erlenmeyer flasks (125mL)

3. Mortar and pestle

4. Volumetric flask(50mL)

5. Filter paper

6. Burettes

1. Safety and Waste Disposal:

Safety : Always wear your coat, gloves and eye protection.

1. Procedure:

Part. A (Vitamin C tables)

1. Take a table of Vitamin C, and find its weight.
2. Use the mortar and pestle to make it into powder.
3. Quickly use KBrO₃ to titration it until it become a little bet yellow. Write down its weight.
4. Add 0.5g KI, and add 5mL starch with water after KI is totally dissolute. Then use Na₂S₂O₃ to titration it until it is not looking blue. Write down the amount of Na₂S₂O₃ that had been used.
5. Calculate the amount of each of the Vitamin C table.

Part. B (Juice)

1. Filter about 100mL of juice.
2. Put 20mL of juice from step one to a 50mL volumetric flask. Then add 0.5g KBr and fill the volumetric flask with 1M H₂SO₄. Put it in a Erlenmeyer flask, and then start to titration as fast as possible. Write down the Vitamin C in the juice.
3. Take another 20mL juice and put in another Erlenmeyer flasks and put in hot water with a stopper for 20 minutes. After it cold down, Put it in a volumetric flask. Add 0.5g KBr and fill the volumetric flask with 1M H₂SO₄. Put it in a Erlenmeyer flask, and then start to titration as fast as possible. Write down the Vitamin C in which is destroyed because of heat.
4. Take another 20mL juice and put in another Erlenmeyer flasks and stir hard in the air for 20 minutes. Put it in a volumetric flask. Then add 0.5g KBr and fill the volumetric flask with 1M H₂SO₄. Put it in a Erlenmeyer flask, and then start to titration as fast as possible. Write down the Vitamin C in which is destroyed because of the reaction with air.

1. Results:

1. Discussion:

It is really hard to control the titration’s speed. We obviously fail 3 times, so we need to restart it. And the second try we just do it as good as possible. This time, we just did it. And the second Erlenmeyer flask’s Vitamin C is a little bit too much, we think it maybe is because we make some accident while we are titration. Because even a little bit more or less, the change is very huge.

1. References:

Wikipedia

1. Reflection and Feedback:

The second bottle of vitamin C is too big so it could be some kind of error.

And the other two number is close to each other, I think is because the second one we add too little Na₂S₂O₃ so there are not the real data or just others we stop too slow then the last titration is too over.