Objective 1:

Use a qualitative method to determine whether starch is present in four solutions [A–D] and, if so, the relative concentration of starch in each solution.

Background

On the lab bench, there are four solutions containing unknown concentrations of starch, labeled in bottles: A, B, C, and D. It is possible that one of the solutions does not contain starch. Discuss and agree on an approach with your group that will allow you to:

1. determine whether or not there is starch in the solutions, and

2. place the test tubes A–D in order of lowest to highest starch concentrations.

Available Tools and Equipment

• Four bottles, labeled A–D, each containing a starch solution of unknown concentration

•  I2KI (0.1 to 0.3 ml)

• Syringes (note that syringes are labeled with colored tape)

• Spectrophotometer tubes and corks

 • Test tube rack

• Stock starch solution (concentration: 10 g/l)

Ideas to Consider

• Before you begin your experiment, practice using the syringe to draw up liquid and release it. Be careful and exact in your measurements. Notice that the syringes have two different numbering systems (1 cc = 1 ml).

• Why is it important to use a different syringe for each solution?

• How much liquid does a test tube hold?

• What do qualitative results tell you?

• You will need at least 4 ml of solution in your tubes for accuracy.

Objective 1: Experimental Design and Results Carry out your experiment and take notes below describing what you did and how your experiments helped you achieve

Objective 1. Your descriptions should be clear and complete enough so that someone else can follow your logic and repeat your tests if necessary.

Although you should discuss this as a group, your written work should be your own and will be graded as such by your GTA.

When you are done, please dump and wash test tube contents down the sink. Wash out your tubes and place back in test tube racks.

Please read the “Available Tools and Equipment” AND “Ideas to Consider” sections on page 99.

Then in your group, determine a plan to carry out your experiment. Fill out the Experimental Design Section below and show it to your GTA BEFORE you begin.

❏ Prediction: What sort of results do you expect to see if the tubes have varying starch concentrations?
❏ Procedure: Provide sufficient detail so that another classmate could replicate your methods.