Idk Lab

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So long, Gummy Bears!
[pic]

This demonstration illustrates the vast amount of energy which is available from the oxidation of carbohydrates, such as sugar. An excess of oxygen, generated by the decomposition of potassium chlorate, will react with the glucose in a gummy bear, releasing a large amount of energy quickly and dramatically.

Introduction:

Sugar is a fuel that we use for energy. We can also use it to fuel a chemical reaction. In this reaction, the sugar from the gummy bear reacts with the oxygen produced from the decomposition of potassium chlorate. Purple sparks form, which are a result of the potassium ion (it has nothing to do with the colour of gummy bear you use).

As we heat the Potassium Chlorate it starts to decompose as follows:

2KClO3(s) ( 2KCl(s) + 3O2(g)

This produces oxygen which oxidizes the sugar (glucose) in the gummy bear. This oxidation is incredibly exothermic (-5000 kJmol-1). The reaction is:

C6H12O6(s) + 6O2(g) ( 6CO2(g) + 6H2O(g)

The glucose molecule is shown in structural form below:
[pic]

Materials Needed
• one 25x150 mm Pyrex test tube
• one ring stand with clamp for test tube
• 5-7 grams potassium chlorate
• Bunsen burner
• one candy gummy bear (or any other candy - M&M’s, gum drops etc.)

Caution! This reaction produces a large quantity of heat, flame, and smoke (mostly water vapour). It should be done in a well ventilated room, or, preferably, in a fume hood. Potassium chlorate should be used with caution. It is a strong oxidizing agent, especially when molten. Keep all combustible materials away from the reaction area. Make sure the test tube used is scrupulously clean and the mouth is pointed away from the audience. Procedure: Set up the stand and clamp, and support the test tube in the clamp in a vertical position. Add 5-7 grams of potassium chlorate to the test tube (about 1 cm in depth). Gently heat the tube with the burner until the potassium chlorate is completely molten. Bubbles of oxygen will begin to form. Remove the burner and use crucible tongs to drop in the gummy bear, and stand back! If you don’t have the proper chemicals or equipment to perform this demonstration, you can view the reaction at the following websites:

www.Mrstyles.co.uk/html/screaming_baby.html

http://video.google.com/videoplay?docid=4376433037022171750&q=gummy+bear

(I couldn’t make a direct link to these websites for some reason)

Student Analysis:

1. What is a decomposition reaction? 

2. Write a balanced reaction for the decomposition of potassium chlorate. 

3. How could we test for the presence of oxygen in this decomposition reaction? 

4. Why is it necessary to heat this reaction? 

5. What is the difference between an endothermic and an exothermic reaction?

6. Write a balanced reaction for the oxidation of glucose. Show, using oxidation numbers, which substance is oxidized and which substance is reduced in the reaction. Also state the oxidizing agent and the reducing agent.

7. What caused the Gummy Bear to explode? 

8. Observe the products of this reaction. Did the reaction go to completion, forming only CO2 and H2O? What would the products include if the combustion was incomplete?  

Summary: When heated, potassium chlorate decomposes, producing sufficient oxygen to ignite the sugar in the gummy bear. Since the oxidation of the sugar is very exothermic, sodium chlorate continues to decompose to oxygen, and the rate of combustion becomes very rapid.

The chemical equations for this demo are:

2KClO3(s) ( 2KCl(s) + 3O2(g)

C6H12O6 + 6O2 --> 6CO2 + 6H2O

The heat from the Bunsen burner is used to increase the rate of reaction. The glowing splint will re-light once there is a presence of oxygen, meaning that the decomposition reaction...
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