Vitamin C Excretion Problems

Remember to set up a table to record and process your titration data as follows:

aliquot size being titrated:________ mL

conversion factor of iodine being used: _________ mg vitamin C/mL iodine

 

	Trial I	Trial II	Trial III
finish:
start:	_–_________	_–_________	_–_________
iodine used:

The start for trial II should equal the finish of Trial I, etc (assuming no leakage of titrant between titrations). Once the three flasks are titrated, you average the iodine used by adding them up and dividing by three.

The answers to the problems are at the bottom of the page.

PROBLEMS:

1. Standardization:
1.00 mL aliquots of 1% ascorbic acid were titrated in triplicate with iodine of unknown strength.  Successive readings on the buret were: 12.94, 24.35, 35.73, 46.00 mL.  What is the conversion factor for this iodine?

2. Assay of urine:
10 mL aliquots of urine were titrated in triplicate with iodine having a conversion factor of 0.932 mg vitamin C/mL iodine.  The following are successive readings on the buret:  15.91, 16.08, 16.28 and 16.47 mL.  What is the average amount of vitamin C in the 10 mL aliquot?

3. Assay of orange juice:
5 mL of orange juice was found to contain 2.37 mg of vitamin C.  How much vitamin C is there in 100 mL?

4. Calculation of urine production:
What is the urine production rate per hour if the bladder was voided at 2:30 and 510 mL was collected at 4:30?

5. Calc. of Vit C excretion rate: 
If a person produces urine with 1.43 mg vitamin C/10 mL aliquot, and they produced 167 mL in an hour, what is the excretion rate/hr?

6. Calculation of urine production:
A person who drank a lot of Coke produced 230 mL in 20 minutes.  What was their urinary production rate per hour?

7. Calculation of urine production:
A person voided after breakfast at 8:27 AM.  At 12:15 PM, he produced a total of 396 mL of urine.  What was his hourly rate of urine production?  (Hint: express total time as hours, calculating fraction of hr as # of minutes/60)

8. Calculation of urine production:
A poor A&P student voided her bladder at the beginning of Lab (2:12 PM–she came in late…).  At 4:12 PM, she produced 438 mL of urine.  What is her rate of production of urine per hour?

9. Calc. of Vit C excretion rate: 
The student in the previous question titrated 10 mL of urine from question 8 in triplicate with iodine whose conversion factor was  0.729 mg vitamin C/mL iodine.  She got the following successive numbers: 12.01, 14.79, 17.51 and 20.53 mL.

a: What was the content of vitamin C in 10 mL of her urine?
b. What was the total number of 10 mL aliquots which she produced in an hour?
c: What was the total amount of vitamin C which she excreted in an hour?

(Here is problem 9 worked out if you would like to compare it to your work.)

Answers:

1.  0.907 mg vit C/mL iodine
2.  0.174 mg vit C/10 mL
3.  47.4 mg vit C/100 mL
4.  255 mL/hour
5.  23.9 mg vit C/hr
6.  690 mL/hr
7.  104 mL/hr
8.  219 mL/hr
9a.  2.07 mg vit C/10 mL
9b.  21.9 aliquots
9c.  45.3 mg vit C/hr