Determining if a Substance is a Sugar, a Starch, a Protein, or a Lipid

We were given four unknown substances (A, B, C and D), and we had to figure out which one was a sugar, a starch, a protein, or a lipid. What did we do? We performed four simple tests that, for the most part, with a color change told us the results. We did them one at a time so we could eliminate a substance per test. The first test we did was the Biuret test in which we found that none of the substances were proteins, and; therefore we could not eliminate any of the substances. Second, we did the Benedict’s test in which we only saw a change in substance A, which lead us to believe that substance A was a sugar. After eliminating substance A, we did the brown paper test that does not have a color change for a result but lives an oil spot which is simple to identify. The presence of an oil spot on the brown paper told us that substance C was a lipid. Finally, we preformed the iodine test on the last two substances, which showed us that substance B was starch because it reacted and cha...