1. Pre-Lab Discussion
Carbohydrates – primary function is to provide energyg
Carbohydrates can be categorized based upon structure
Polysaccharide - many
Disaccharide - two
Monosaccharide – one (simple or single sugar)
“How do you know what type of carbohydrate is in a solution or even a food?”
Use an Indicator – a chemical which tests for the presence
of a given compound

2. Two Indicators in the Lab
Benedict’s Solution
“Which type of carbohydrate will this indicator identify?”
Iodine (Lugol) Solution
“Which type of carbohydrate will this indicator identify?”
Is there a 3rd Indicator in this lab? No
Is this a problem?
Begin the Lab Reminders:
*Bendict’s soln is heat activated *Iodine is not

3. Post Lab Review for _________________________________
Reviewing the lab: Answer in notebook in complete sentences. Be ready to read your answer out loud.
What happens to the color of an indicator if the substance for which it is tested is present in the solution or food?
Explain why the water when mixed and heated with Benedict’s solution remained blue.
Predict and describe what would happen if Iodine and water were mixed together. Explain.
What is the difference between a positive control and negative control?
In an experiment there is always a control. Recall, a control is a setup that does not contain the variable (something that causes the change). Another attribute of a control is that it yields an expected result. The experimental setup has what is being tested or causing the change, or we are unsure. That is why it is an experiment. Which part of the lab do represents the control setups and which part of represents the experimental setups? Explain.
Testing for Carbohydrates in Foods Lab

4. Testing for Carbohydrate in Foods
This presentation illustrates observations which you should have seen during the lab investigation. It presents the accurate color changes with known substance.

5. Results of a Benedict’s Solution Test
The tube on the left is a negative Carbohydrate test result. Color is the original blue of Benedict’s. As you move from left to right, the Benedict’s solution changes from green to orange to red. All three tubes a are a positive test for a carbohydrate. The red indicates the presence of the monosaccharide.

6. Why does Benedict's Solution change color?
Click on the link and get an explanation of the diagram. How does it relate to the picture in the previous slide?

7. Something Fun to Look At
Read the list of substances. Are all carbohydrates? Why do the results appear the way they do?

8. Results for Iodine Test for Carbohydrates
On the right is a test tube of iodine and water. It is a amber color. The test tube on the left contains iodine and a polysaccharide solution. Note the color is no longer amber but a bluish black color.
Why causes the bluish black color?

9. Check out the results for some common foods and beverages

10. Post Lab Questions to be done to help review for lab test
Post Lab Questions to be done to help review for lab test. Can you answer these questions?
Which foods were monosaccharaides?
Which foods were disaccharides?
Which foods were polysaccharides?
What changed color to identify apple juice as a monosaccharide?
What test tube(s) can be used to help identify if a food is a monosaccharide?
Which test tubes serve as positive controls? Why?
Did the experiment contain negative controls?
Write a conclusion for this investigation.