Science Buddies: "Ask an Expert"

My daughter completed the project about how much fat is in different foods. For the chocolate she used unsweetened baking chocolate. The resulting fat was a very dry, crumbly fat and it was between 70-80% fat versus the nutrition label which said 50% fat. In the other two foods (potato chips and almonds) she was slightly under the % fat shown on the label which seems to be more common. Do you know why her results would show a great % fat than is correct? Would using chocolate chips perform better?

Thank you!
Alison Cannon

Hi Alison,

I’m assuming that you’re working on the project described here:

https://www.sciencebuddies.org/science- ... od#summary

The high fat content result for your chocolate sample could be due to some leftover acetone in the fat extract. Assuming the weights and measures suggested in the project procedure, your result indicates that the extract mass was 2 g too high (70% of 10 g vs 50% of 10 g). The 2 g excess represents about 2.5 ml of acetone (density of 0.79 g/ml) or about 6% of the 40 ml used for the extraction.

My suggestion is to repeat the experiment with the chocolate sample. After completing the extraction, weigh the extract jar every 8 hours (or so) to track the weight loss due to acetone evaporation. The evaporation is complete when the weight doesn’t change with time.

I hope this helps. Please post again if you have more questions.

A. Norman