Day 42: Vitamin C Analysis


Science 9 Students spent the class performing a lab where they use an indicator to determine relative amount of vitamin c in fruit drinks.  The lab was too complex for them to design all of their own procedures.  Instead, the lab is broken into two parts.  In Part A, students are given a dark blue iodine starch solution and a vitamin c tablet.  There job was to crush the tablet into a 100 mL water solution and then slowly dropwise add the solution to the iodine.  At some point the dark blue turns clear, indicating that the vitamin c has reacted with all of the iodine.

For Part B the students were to design a procedure for using the above calibration to determine the amount of vitamin c in different juices.  This proved to be quite difficult for some groups.  Several then started off with fruit juices and added the iodine solution to it dropwise.  They couldn’t see any colour changes, other than dilution, because should have been adding the juice to the iodine. I was a bit surprised at how many groups got this wrong. What didn’t surprise me is how almost all students immediately starting working on the lab prior to actually clarifying and writing a procedure.

The majority of students were able to use good reasoning and determined that apple juice, which took the fewest number of drops to clear the blue iodine colour, had the most vitamin c.

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