Bio- Cell

Cells Chemistry: Experiment

Instructions (Lab Report)

LEARNING GOALS

By the end of this unit, you should be able to do the following:

1. Describe the difference between organic and inorganic chemicals.

2. Relate oxygen content of a chemical to whether it is hydrophilic or hydrophobic.

3. Explain the relationship between starch, fiber, and complex carbohydrates and how

they relate to glucose, sugar, and simple sugars.

4. Describe how to use iodine, Benedict, and Biuret tests to identify starch, simple

sugars, and protein respectively.

5. Describe the color of a positive reaction and a negative reaction for iodine, Benedict,

and Biuret tests.

6. Describe how an emulsifier changes the mixing of oil and water.

7. Identify the Independent, Dependent, and Control Variables in your experiment.

MATERIALS NEEDED

1 bottle of iodine (Get "Iodine Tincture" or Betadine antiseptic in the pharmacy section.

DO NOT use decolorized iodine.)

1 bottle of blue or green food coloring

1 small potato

1 small onion

1 leaf of lettuce

1 stick of butter

1 egg yolk

vegetable oil (or other type of cooking oil)

tap water

sugar

corn starch

4 “starchy” foods from your kitchen (foods you think contain starch)

- Choose 1 liquid and 3 solids

3 “fatty” foods from your kitchen (foods you think contain 25% fat or more)

- Determine fat content by taking the grams of fat on the nutrition label by the total

gram weight of the serving. If the food is a liquid, divide by the total mL volume

as each mL is approximately 1 gram.

- Common fatty foods include artificial cheese (American or “sliced” cheese),

cheddar cheese, salad, bologna/potted meat (mash up first), potato chips, pork

rinds, chocolate candy, mayonnaise, peanut butter, and uncooked sausage or bacon

(chop up first).

3 – 6 drinking glasses

Coffee pot or microwave

Don't forget to fill out the Experiment Tracking Sheet for each section of the

exercise. Remember to take no more than 4 pictures for the lab report.

COMPLEX CARBOHYDRATES

Iodine turns blue-black in the presence of starch, but not fiber. You will be mixing iodine

with water, corn starch, lettuce, table sugar, vegetable oil, potato, onion, and three

“starchy” foods from the kitchen to test for starch.

Iodine Test

1. In a clear container, add several drops of iodine to 1/4 cup of water in a drinking

glass. Mix and observe. Notice the orange or amber color of iodine. This means

there is no starch present. This is a negative control experiment; keep it for

reference.

2. In a clear container, add 1/2 teaspoon of starch to 1/4 cup of water in a drinking

glass. Mix and observe the cloudy white color of starch. Add several drops of

iodine. Mix and observe. Notice the iodine/starch solution has turned black or

dark purple. This means there is starch present. This is a positive control

experiment; keep it for reference.

3. Tear a small lettuce leaf and drop iodine on the torn edge. Notice that the leaf may

turn a light orange, just like the water, but doesn’t turn black. This is another

negative control experiment showing that iodine doesn’t turn fiber black.

4. (Hypothesis) Repeat the test with sugar water, vegetable oil, and any of the

“starchy” foods you chose that are liquids.

5. Cut a small cube of potato, onion and a chunk from each of the three “starchy”

foods you chose that are solids.

6. (Hypothesis) Add several drops of iodine to each and observe the color for amber

or black color.

Conclusions - Which foods contained starch? Which did not? How did your hypothesis

match your results?

LIPIDS

Hydrophobic chemicals (like fat and other lipids) do not mix with water. Hot water mixed

with a food will melt the fats and cause them to float to the top in little bubbles or even a

complete layer. However, if an emulsifier is present, the fats will stay mixed with the

water. You will be mixing hot water with butter, egg yolk, and three “fatty” foods from

the kitchen to test for emulsifiers.

Test for Emulsifiers

Safety Note – This is the most dangerous experiment you will do all semester because you

will be working with hot water and drinking glasses. DO NOT touch drinking glasses

with your bare skin once hot water has been added. Wait at least 15 minutes for the water

to cool down before touching with bare skin.

1. Heat water to steaming in a coffee pot, the microwave, or from a very hot tap. DO

NOT boil water. (If using the microwave, use a microwave safe container and

heat in 30 second increments to avoid boiling.)

2. Add 1 cup of hot water to a drinking glass. Add a tablespoon of butter (1/8th or a

stick) to the hot water and stir for 30 seconds. Let the cup sit for 5 minutes.

3. Note the bubbles or layer of oil floating on top of the water. Add 1 drop of blue or

green food coloring and mix again. Note that the top layer does not absorb the

dye. The floating oil that excludes the dye means there is no emulsifier present.

This is a negative control; keep it for reference.

4. Separate an egg yolk from the white and break up the yolk in the bottom of a

drinking glass. (See YouTube for videos on how to separate an egg yolk.) Add 1

cup of hot water and stir for 30 seconds. Let the cup sit for 5 minutes.

5. Note that the egg yolk (which is 33% fat) stays mixed with the water. Add 1 drop

of blue or green food coloring and mix again. Note that the dye mixes throughout

the glass. The lack of floating oil and the complete mixing of the dye means there

is emulsifier present. This is a positive control; keep it for reference.

6. (Hypothesis) Repeat the test with your three “fatty” foods. If the food is dry,

crush or tear it up before adding to the glass.

Pictures Note – Oil bubbles don’t show up well in pictures unless you turn on the flash.

If you use a flash, the bubbles will become REALLY obvious.

Conclusions - Which fatty foods contained an emulsifier? Which ones didn’t?

ADDITIONAL TESTS

In addition to these tests, you are responsible with knowing the Benedict Reagent test for

sugars and the Biuret Reagent test for proteins. Click on the item "Additional Tests" to

see pictures of these two tests.

QUIZ

You will complete a lab quiz over the lab.

LAB REPORT

Your first full lab report will be written over this lab. The lab report instructions are

contained within this module. Consult the schedule located in the "Welcome Module" inside of the "Syllabus & Schedule" subfolder.

Note that you must include 2 tables for this report: 1 table for the Iodine Test and 1 table

for the Emulsifiers Test.