Reactions!

What To Do

Introduction

• Discuss the differences between a chemical and a physical reaction.
  • Examples of physical reactions: cutting wood, popping popcorn, melting water
  • Examples of chemical reactions: burning wood, rotting meat, forming a precipitate.

Activity 1: Decomposition Reaction

• Explain what a decomposition reaction means (larger molecules are broken down by smaller ones).
• Set up the elephant toothpaste reaction. 
• Get them to open the yeast packet and pour it into a cup with 3-4 tablespoons of warm water. 
• They will stir the yeast until it is dissolved. It should start to smell like "bread".
• Afterwards, instruct students to put the bottle on the plate/bowl. Carefully pour all the hydrogen peroxide from the tube into the graduated cylinder. 
• Tell students to add a few drops of food colouring and a good squirt of dish soap.
• Ask questions such as:
  • "Why do you think we are adding the soap?"
  • "Has any chemical change occurred?"
• Have students carefully and quickly pour the yeast into the cylinder and observe.
• Discuss observations.
• For fun, play the video of Science Bob Elephant's Toothpaste. 

Activity 2: Synthesis Reaction

• Explain what a synthesis reaction means (smaller molecules come together to make a larger molecule).
  • Photosynthesis is a great example of a synthesis reaction. Carbon dioxide gas and water combine in the presence of light/sunlight to make sugar and oxygen gas.
• Discuss polymerization.
• Play the video Instant Worms from Steve Spangler Science

Activity 3: Ionic Reactions

• Discuss what an ion is and the two type of ionic reactions - single and double displacement. 

Single Displacement

• Have students pour a little bit of coke out of their bottle, or pour some into a glass.
• Have them add milk to the bottle/glass, leaving some space at the top.
• Let it sit for a few minutes and observe what happens.
• Explain the reaction between the phosphoric acid in the soda pop and the calcium in the milk to make tricalcium phosphate and hydrogen.

Double Displacement

• Have students add vinegar to a cup and 1 tsp. of baking soda. 
• Ask them questions such as:
  • 'What did you observe?"
  • "Does anyone know what's happening chemically?"
• This is an example of a double displacement reaction. Explain that the sodium and hydrogen ions exchange and carbonic acid is produced. The carbonic acid is unstable and readily decomposes to CO₂ gas and water.
• Have students add a teaspoon of baking powder to the milk/water, stir for about 2 seconds. 
• Ask questions such as:
  • "Is this a chemical or physical change and why?"
• This is an example of a double displacement reaction. Explain that the bicarbonate ion removes a hydrogen from the bitartrate ion.
• Discuss the application of displacement/ionic reactions in catalytic converters. 

Discussion: Combustion Reactions

• Play the video Death of a Gummy Bear. 
• Discuss what a combustion reaction means.
• Go over the reaction steps from the video above. 
  • First, potassium chlorate is heated to change it from a solid to a liquid (produces potassium chloride and oxygen).
  • The gummy bear was dropped into the liquid containing oxygen. The sugar reacted to produce carbon dioxide and water and energy in the form of heat and light.

Wrap-up

• Review each reaction and ask students to share their observations.
• Discuss possible careers related to the topics discussed in today's workshops and what you need to do (education, experience, etc.) to get into those careers.