8th Grade Lab Science (Cribb & Duane)
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Lab Activity: Organic Compound (Carbohydrates) Testing Using Chemical Indicators

 

Objective: By the end of this lab activity, you should be able to relate specific compounds with their chemical indicators, and tell positive or negative results for the three types of carbohydrates Ė monosaccharides (simple sugars); disaccharides (complex sugars); and polysaccharides (starches).

 

Directions: Each member of the lab group needs to record the results of each chemical test in his lab notebook, and tell what each test tells him about the presence or absence of the chemicals being tested.  Make sure you wear safety goggles for this lab activity.

 

Lab Instructions Part I: Testing Known Substances

 

In Part I, you will you will conduct chemical tests on known substances and water.  Part I will serve as a control. 

 

Note: 1.0 mL = 20 drops from a pipet or dropper.  All substances are in solutions.

 

  1. Chemical Test for Polysaccharide (Starch)

 

a.      Number test tubes #1-4

b.     To each test tube, add the following:

 

1.       1.0  mL monosaccharide (simple sugar)

2.     1.0 mL disaccharide (complex sugar)

3.     1.0 mL polysaccharide (starch

4.     1.0 mL water

 

c.      Record the color of each solution before adding any chemical indicator.

d.      Add 5 drops of iodine solution to each test tube.

e.      Record the color of each test tube.

 

  1. Chemical Test for Monosaccharide

 

 

a.      Number test tubes #1-4

b.     To each test tube, add the following:

 

1.       1.0  mL monosaccharide (simple sugar)

2.     1.0 mL disaccharide (complex sugar)

3.     1.0 mL polysaccharide (starch

4.     1.0 mL water

 

c.      Add 1.0 mL of Benedictís solution to each test tube.

d.      Record the color of each test tube.

e.      Place the test tubes in a hot water bath.  This is a beaker filled with hot water.  For this chemical test, this will speed up any reactions.  Be careful not to over heat as this may give a false positive.

f.      Record the colors of each test tube after heating.

 

 

  1. Indicator Paper for Monosaccharide

 

a.      Number test tubes #1-4 or you may use a spot plate.

b.     To each test tube or well, add the following:

 

1.       1.0  mL monosaccharide (simple sugar)

2.     1.0 mL disaccharide (complex sugar)

3.     1.0 mL polysaccharide (starch

4.     1.0 mL water

 

c.      Record the color of each solution before adding any chemical indicator.

d.      Dip a strip of Tes Tape into each test tube or spot plate.

e. Record the color of the Tes Tape.

 

 


Lab Instructions Part II: Testing Unknown Substances

 

In Part II, you will conduct chemical tests on various sugars and starches and determine whether each is a monosaccharide (simple sugar), disaccharide (complex sugar), or polysaccharide (starch). 

 

You will conduct test A (iodine solution), test B (Benedictís solution), and test C (Tes Tape) on the following substances.  All of the substances are types of carbohydrates.

 

Amylose

Glucose

Fructose

Sucrose

Lactose

 

 

  1. Chemical Test for Polysaccharide (Starch) Using Iodine Solution

 

a.      Number test tubes #1-7

b.     To each test tube, add the following:

 

1.       1.0  mL amylose

2.     1.0 mL glucose

3.     1.0 mL fructose

4.     1.0 mL sucrose

5.     1.0 mL lactose

6.     1.0 mL polysaccharide (starch)

 

c.      Record the color of each solution before adding any chemical indicator.

d.      Add 5 drops of iodine solution to each test tube.

e.      Record the color of each test tube.

 


  1. Chemical Test for Monosaccharide (Simple Sugar) Using Benedictís Solution

 

 

a.      Number test tubes #1-8

b.     To each test tube, add the following:

 

1.       1.0  mL amylose

2.     1.0 mL glucose

3.     1.0 mL fructose

4.     1.0 mL sucrose

5.     1.0 mL lactose

6.     1.0 mL monosaccharide (simple sugar)

7.     1.0 mL disaccharide (complex sugar)

 

c.      Add 1.0 mL of Benedictís solution to each test tube.

d.      Record the color of each test tube.

e.    Place the test tubes in a hot water bath.  This is a beaker filled with hot water.  For this chemical test, this will speed up any reactions.  Be careful not to over heat as this may give a false positive.

f.     Record the colors of each test tube after heating.

 

 

  1. Indicator Paper for Monosaccharide (Simple Sugar) Using Tes Tape

 

a.      Number test tubes #1-8 or you may use a spot plate.

b.     To each test tube or well, add the following:

 

1.       1.0  mL amylose

2.     1.0 mL glucose

3.     1.0 mL fructose

4.     1.0 mL sucrose

5.     1.0 mL lactose

6.     1.0 mL monosaccharide (simple sugar)

7.     1.0 mL disaccharide (complex sugar)

 

c.      Record the color of each solution before adding any chemical indicator.

d.    Dip a strip of Tes Tape into each test tube or spot plate.

e.    Record the color of the Tes Tape.

 

 

Questions:

  1. If you were testing an unknown solution for starch, how would you know if starch is present or not?

 

  1. What is the reason for test tubes #6 & #7 in Part II?

 

  1. When you conduct a chemical test using Benedictís solution, why do you need to apply heat?

 

  1. How could you determine if an unknown substance were a disaccharide (complex sugar) from noticing the results of both monosaccharide (Benedictís & TesTape) tests?

 

  1. Which of the unknown substances are polysaccharides (starches)?

 

  1. Which of the unknown substances are monosaccharides (simple sugars)?

 

  1. Which of the unknown substances are disaccharides (complex sugars)?

 

 

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LAB HANDOUTS:

Lab Handout: Using Chemical Indicators to Test for Carbohydrates

Data Table (blank): Results of Using Chemical Indicators to Test for Carbohydrate

Summary Table of Indicators & Known Carbohydrate Testing

Results of Chemical Tests on Unknown Carbohydrates

 

REFERENCE

Results of Controls (Indicators on known substances)

Chapter 9: It's Alive - Organic Compounds Essential for Living Things