Sample Laboratory Report

Kudos to the following people for getting excellent precision on their acid/base titrations:

Julie Barer Chris Phillips Jim Anderson	0.0066
Sara Banks Julie Bosacker	0.0050
Allison Watkins Claire Campbell	0.0071
Cathleen Johnson	0.0025

Laboratory #7 --- 3 April 1998

Changes to Laboratory Manual

Laboratory #6 --- 20 March 1998

Changes to Laboratory Manual

1. On page 6-3, Part C - Second line….. The line should read as follows: "…and 6.0 mL of water in a 125 mL Erlenmeyer flask. Using a graduated cylinder, add 5.0 mL of sample 1 (boiling water from…" The text in blue was inadvertently omitted.
2. On page 6-6, Question 3 should read as follows: "Determine the total recoveries of Vitamin C from the boiled and steamed samples. Total % Vitamin C = % Vitamin C in cooking water + % Vitamin C in pepper. What may account for the differences in the recoveries between the steamed and boiled samples?"
3. In the appendix to Experiment 6 (page 6-7), a subscript 2 was omitted from the second chemical equation. Iodine is produced not just I.
   

Important Things to Note or Remember

1. You will prepare a total of 5 liquid samples for ascorbic acid analysis. Save both the water used to steam and boil the green pepper as well as the pieces of pepper!
   Sample 1: Water used to BOIL green pepper;
   Sample 2: Water EXTRACT of BOILED green pepper;
   Sample 3: Water used to STEAM green pepper;
   Sample 4: Water EXTRACT of STEAMED green pepper;
   Sample 5: Water EXTRACT of RAW GREEN PEPPER.
2. Read your buret volumes to TWO decimal places (e.g. 20.17 mL)
3. Sample 5 serves as your control. It should provide the total amount of vitamin C contained in a raw pepper prior to any cooking. BY DEFINITION the % recovery of ascorbic acid from raw pepper is 100%!! (You can't have any more Vitamin C than that which is present in the original material or foodstuff)
4. Do your % recovery values make sense? Should they be lower or higher than 100% (i.e. the raw pepper)?

Laboratory #5 --- 13 March 1998

Changes to Laboratory Manual

1. On page 5-3, SOAP TEST - Number 2….. CROSS OUT cold tap water and REPLACE WITH deionized water.
2. On page 5-3, EDTA TITRATION - Number 1…. Change Appendix reference from 4 to 3.
3. Perform the soap tests BEFORE doing the EDTA titrations. This will give you a "ballpark" estimate of the water hardness. When making the calibration curve, the standards having a lot of calcium will create soap scum on the sides of the test bottles. Try your best to discriminate between soap suds and soap scum.

Water Hardness
ppm Calcium carbonate	Designation
0-43	Soft
43-150	Slightly Hard
150-300	Moderately Hard
300-450	Hard
>450	Very Hard

Laboratory #4 --- 6 March 1998

Changes to Laboratory Manual

Last Modified 12 March 1998 P. T. Jackson

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