October 20, 2009
* Add a small piece of cracker in test tube #1 and add Lugol’s solution.
* The cracker turned a black colour when the Lugol’s solution was added to it. This was a positive result, meaning that the cracker contains starch.
* Add a bigger piece of cracker in test tube #2, add 5 mL of Benedict’s solution, place in a boiling water bath, and record observations after 5 minutes.
* There was no change in colour after the Benedict’s solution was added to the cracker. This was a negative result, meaning that the cracker is not a mono- or di- saccahride.
* Chew a cracker for 2 minutes, then spit the sample into test tube #3 and add Lugol’s solution. Let sit for 15 minutes and observe what happens
* The solution turned a black colour when the Lugol’s solution was added to it. This was a positive result, meaning that cracker contains starch.
* Chew a piece of cracker for 2 minutes without swallowing, then spit sample into test tube #4, let sit for 15 minutes, add 5mL of Benedict’s reagent, place test tube in hot water bath, and record observations after 5 minutes.
* When the solution was added to the hot water bath, the solution went from blue, to green, to yellow, and finally to orange as time progressed. This was a positive result, meaning that the amylase in our saliva broke the polysaccharides in the cracker into mono- and di- saccharides. As a result, the Benedict’s reagent changed colour because it indicated the presence of mono- and di- saccharides in the solution.
There weren’t any differences in the results of step 4 when compared with the results of step 2. This is because all the Lugol’s solution is doing is indicating if starches are present. Starches are present no matter if the cracker is solid or...
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