Vitamin C Titration Lab Prep What formulas or calculations w

Vitamin C Titration Lab Prep: What formulas or calculations will I need for this lab? How do I answer questions once I get the data? I don\'t have the info yet as it is for tomorrow, but I would like to be a bit prepared.

Sample 1 20.0 mL Sample 2 1. Volume of juice pipetted (mL) 2. Final buret reading for i, solution (mL) 3. Initial buret reading for l2 solution (mL) 4. Volume of iodine solution used (mL) 5. Molarity of I2 solution 6. Moles of l2 20.0 mL (molarity of 12 × liters 12 solution used) 7. Moles ascorbic acid in sample (equals moles 2 used) 8. Milligrams ascorbic acid in sample 9. Milligrams ascorbic acid per mL juice 10. Average milligrams ascorbic acid per mL juice. (moles ascorbic acid x 176.1 g/mole x 1000 mg/g) (show calculation)

Solution

1) a) final burette reading for iodine solution u will get from titration

b) initial burette reading is always zero ml

c) Volume of iodine solution used = average of 3 final burette readings

d) Molarity of iodine is given by teacher

e) for columns 6,7,8 formulae already given in those respective columns

f) Milligrams of ascorbic acid per ml of sample:

assume, you got 10mg ascorbic acid in sample

20ml sample = 10mg ascorbic acid

1ml sample = (10 x 1) / 20 = 0.5mg/ml ascorbic acid

g) Average mg ascorbic acid per ml sample:

(mg ascorbic acid per ml of sample A + mg of ascorbic acid per ml of sample B) / 2

h) Amount of ascorbic acid in one cup orange juice:

1 cup = 236.5ml

Assume, 1ml sample = 0.5mg ascorbic acid

therefore, 236.5 ml sample = (236.5 x 0.5) / 1 = 118.25 mg of ascorbic acid in 236.5ml sample

Note:

In points f) and h) i have taken an imaginary value i.e. 10mg 0f ascorbic acid and 0.5mg of ascorbic acid. You have to put the values you get in class in the same formula.

2) 1 cup juice = 130% vitamin C = 130g vitamin C in 100ml = 130 x 10³ mg in 100ml .....(1g = 10³ mg)

130 x 10³ mg is present in 100ml

so, 60mg will be present in = (100 x 60) / 130 x 10³ = 0.0462 ml

Therefore, an adult must drink 0.0462ml from that cup to have 60mg of vitamin C

3) This method is used in determination of vitamin C concentration using iodine by redox titration. Vitamin C is also known as ascorbic acid. It is one of the essentia antioxidants for human body.

When iodine is added during titration, ascorbic acid is oxidised to dehydroascorbic acid and iodine is reduced to iodide ions.

Ascorbic acid + I₂ 2I^- + dehydroascorbic acid

Hence, because of this reaction, in presence of ascorbic acid iodine is reduced to iodide ions. When all ascorbic acid molecules are oxidised, the remaining excess iodine reacts with starch indicator to give blue-black starch-iodine complex which is the end point for titration.