MR. OSMAN: Hello, and welcome to this Core Practical video. My name is Mr. Osman, a science
teacher at Claremont High School in London. Today, I'm going to take you to the Core Practicals,
investigating the use of chemical reagents in identifying starch, reducing sugars, proteins,
and lipids. To carry out this experiment you will need the following equipment-- eye protection,
water, 10ml measuring cylinder, spatula, powdered food or suitable food samples, paper towels,
test tube, boiling tubes, racks and bungs, a stirrer, iodine solution and dropper bottle,
Benedict solution, biuret solution, ethanol, dimple spotting tile, and a water bath set
to 70 degrees Celsius. Always remember to wipe the spatula and stirrer in between tests
with a paper towel to prevent cross contamination during the experiment.
To test for the presence of starch, place one spatula of powdered food on a dish or
a spotting tile. Using a dropper, place a few drops of iodine solution onto the food
sample. In your results table, record the letter or name of the food and any changes
in the color of the solution.
To test for the presence of protein, place a spatula of powdered food into a test tube.
Add about one centimeters cubed of the water to the tube and stir to mix. Add biuret solution
to the tube and stir. If you're using potassium hydroxide solution and copper sulfate solution
instead of biuret, you need to add about one centimeters cubed of potassium hydroxide solution
to the tube and stir, then add two drops of copper sulfate solution and stir. Record the
letter or type of food and the color of the solution after a few minutes.
To test for the presence of lipids, the scientific term for fats and oils, place a spatula of
powdered food into a test tube. Add about two to three centimeters cubed of ethanol
to the tube. Place a bung firmly in the end of the tube and shake the tube vigorously.
Allow the content to settle. Pour the liquid from the top of the mixture into a boiling
tube half filled with water. Record the letter of the food and whether the water is cloudy
or remains transparent.
To test for the presence of reducing sugars, place a spatula of powdered food into the
boiling tube. Add one centimeters cubed of the water to the tubes and add equal volumes
of Benedict solution to each one and mix. Place the tubes in a water bath at about 70
Celsius for a few minutes.
Record the letter of the food you have tested and the color of the final solution. Use your
knowledge of the substances the reagent tests for to help you identify the food types from
the list you are given. Your teacher may give you further unknown substances to test to
extend your confidence in the techniques shown within this practical.