Determination of vitamin C content Honors Chemistry

background [prelab assignment (20 points) due at the beginning of lab; put a copy in your lab NB]

what is a calibration (or standard) curve ?

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

sketch a data table (i.e. not calculations) for your experimental measurements (i.e. review the purpose & content of your lab report)

msds on I2 (aq)

purpose

determine / compare the concentration of vitamin C in various samples based on the following reactions

starch (colorless) +  I2  -->  starch - I2 complex (color)

and using a calibration / standard curve.

fulfill various aspects of the NGSS science & engineering standards.

materials

microwell plates; micropipets

aqueous solution of starch, I2 (0.2 g I2 + 0.17 g KI / 200 mL), various [known] of vitamin C, and various fruits / juices

methods

mix 200 µL of a vitamin C solution & 5 drops of the starch solution in a well of a microplate

add and count # drops of the I2 (aq) solution until there is a permenant color change in the solution; record its value

data analysis

student design

 

Content of lab report [35 points]

results (10 points)

calibration / standard curve; include the equation & R2 value for the curve

determination of vitamin C content in your sample; show your work

discussion  [20 points]

statistical data analysis:  comparison of vitamin C content in various samples, include interpretation of p-value

questions

vitamin C is an antioxidant;  what is an antioxidant ?

what are the biological effects of oxidizing agents ?

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

describe / list two NGSS science & engineering practices that correlates to an aspect of this laboratory activity; provide an example in the lab & this lab report that meets these practices

web resource

MS Excel tutorial to curve-fit (i.e. regression analysis; may need to "add-in" analysis tool kit)

lab activity source (examples):  site 1  &  site 2  [access 4 / 2009]