Virtual lab: vitamin C assay [44 points; variable points / question in purple]

 

This virtual laboratory activity is based on the handout to the corresponding in-person lab activity is determine the concentration of vitamin C in various fruits.

background questions [16 points]

1. what is a calibration (or standard) curve ?

2. what is the basis of a least-squares regression analysis ?

3. describe the syntax / protocol in using MS Excel to generate the calibration curve. as appropriate, include sketches / screen shots to clarify your response

4. msds on I2 (aq)

While the video (~ 6 : 20") shows an experimental method, the in-person version of the lab activity uses a lot less chemicals and the mathematical analysis is somewhat simplified. One of reactions in this lab activity is a redox reaction

 [reaction 1]

and the concentration of vitamin C, [vit C], is related to other variables by the equation

[vit C] VvitC = [I2] VI2     [you will learn about this equation later in the course]

and solving for [vit C] is

[vit C] = {[I2] / VvitC} VI2

so a graph of [vit C] versus VI2 will be a straight line with a slope = {[I2] / VvitC}, which is a constant. Excel can do linear regression (note to set the y-intercept to zero) to find the value of the slope, which can then be used to find [vit C], when the VI2 is known..

5. In addition to the preceding chemical equation, there is another chemical equation

starch (colorless) +  I2  -->  starch - I2 complex (color)    [reaction 2]

what is the role / purpose of this reaction ? [5 points]

6. Do the virtual laboratory activity using Excel to simulate the data from the chemical reaction, where you will be given the data to generate a standard (or calibration) curve, then find the concentration of vitamin C in various simulated food items using the standard curve.    Compare the values of the simulated vit C content in the simulated food items , qualitatively, based on 5 simulation trails and the average & standard deviation of the vit C content in the simulated food items. [15 points]

7. addtional questions [9 points]

a. vitamin C is an antioxidant;  what is an antioxidant ?

b. what are the biological effects of oxidizing agents ?

c. based upon the preceding questions, what is a potential biological effect of vitamin C ?