Determination of Fat in a Snickers’ Bar

In a recent paper [J. Chem. Educ. 1997, 74, 1108-1111], Snow, Dunn and Patel describe the experimental determination of fat in a SnickersTM candy bar.  The fat was removed by extraction with supercritical CO2, with the sample weighed before and after extraction.

(a) In a typical analysis a 1.011-g sample of candy was placed inside the extraction vessel along with Celite (an inert substance that just occupies extra space within the extraction vessel).  The weight of the vessel, candy and Celite before extraction was 101.380 g; after seven extractions the weight was 101.109 g.  A blank analysis showed that a loss of 3 mg of Celite per extraction.  Report the % w/w fat in the candy bar.

(b) Shown below are the results, % w/w fat, from 11 separate analysis of a single candy bar.

16.5 18.2 25.8 23.2 24.3 24.3 20.4 18.5 20.6 18.5 23.7

Report the mean, standard deviation, relative standard deviation, and 95% confidence interval for this data.  Explain the significance of each of these values.

(c) The precision of an analytical method can be limited by the sample, the method or the analyst.  Considering the material being sampled, the type of analysis being conducted and the analysts (students like yourself), which do you think will be the limiting factor.  Briefly support your position.

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