I took fresh orange juice and added 40.0 ml to a flask then added 1.0ml of a sta
ID: 1009805 • Letter: I
Question
I took fresh orange juice and added 40.0 ml to a flask then added 1.0ml of a starch indicator solution,
I added 0.015 M of iodine solution to a 50 ml burette.
After 5.67 ml had been dispenced, it changed from orange to dark orange. The volume of the flask was at 46.69 ml.
AFter a repeat with OLD (WEAK) orange juice, it took 2.70 ml dispenced to turn it to darker orange. The flask volume was at 43.71.
1. How many moles of iodine were needed to reach the end point during one of your fine titrations of the fresh orange juice? Choose the closest answer.
A.1.0 × 10-3 moles
B.1.0 × 10-1 moles
C.1.5 × 10-4 moles
D.1.0 × 10-4 moles
2. How many moles of iodine were needed to reach the end point during one of your fine titrations of the week old orange juice? Choose the closest answer.
A.3.5 × 10-4 moles
B.1.0 × 10-4 moles
C.4.1 × 10-1 moles
D.4.1 × 10-5 moles
3. Based on the results of your fine titration, how many moles of ascorbic acid are in 40 mL of fresh orange juice? Choose the closest answer.
A.0.00040 moles
B.0.10050 moles
C.0.00010 moles
D.0.40200 moles
4. Based on the results of your fine titration, how many moles of ascorbic acid are in 40 mL of week old orange juice? Choose the closest answer.
A.1.5 × 10-5 moles
B.4.1 × 10-2 moles
C.4.1 × 10-5 moles
D.2.7 × 10-5 moles
5. Based on the results of your fine titration, how many mg of ascorbic acid are in 40 mL of fresh orange juice? The molar mass of ascorbic acid is 176.12 g/mol. Choose the closest answer.
A.18 mg
B.10 mg
C.37 mg
D.60 mg
6. Which of the following conclusions are consistent with the data you obtained from your orange juice titrations?
A.Vitamin C is highly unstable after one week.
B.Vitamin C is highly unstable, degrading over time.
C.Vitamin C is highly stable for one week.
D.Vitamin C is highly stable over time.
Explanation / Answer
a) 1. How many moles of iodine were needed to reach the end point during one of your fine titrations of the fresh orange juice? Choose the closest answer.
Answer: The moles = Molarity X volume in litres
Volume = 5.67mL = 5.67 / 1000 L
Moles of Iodine = 0.015 X 5.67 / 1000 = 0.0851 millimoles = 0.851X 10^-4 moles, approx D.1.0 × 10-4 moles
2) How many moles of iodine were needed to reach the end point during one of your fine titrations of the week old orange juice
Answer: The moles = Molarity X volume in litres
Volume = 2.70mL = 2.70/ 1000 L
Moles of Iodine = 0.015 X 2.70 / 1000 = 0.0405 millimoles = 0.405 X 10^-4 moles, approx D.4.1 × 10-5 moles
3) the reaction is
ascorbic acid + I2 2 I + dehydroascorbic acid
So each mole of iodine will react with one mole of ascorbic acid present in juice
Moles present in 40mL juice = Moles of iodine used = 1.0 × 10-4 moles = 0.0001 moles
4) he reaction is
ascorbic acid + I2 2 I + dehydroascorbic acid
So each mole of iodine will react with one mole of ascorbic acid present in juice
Moles present in 40mL juice = Moles of iodine used = 4.1 × 10-5 moles
5) Mass of ascorbic acd= Moles X molecular weight = 1.0 × 10-4 moles X 176.12 g / mole = 17.6mg = 18mg
6) B.Vitamin C is highly unstable, degrading over time.