Background

Redox reactions involve two or more chemicals where oxidation states of two or more atoms or ions involved change. (Often it may also involve exchange of oxygen.) The species that undergoes reduction in oxidation state is said to have undergone reduction and labeled as the oxidizing agent. The species that undergoes increase in oxidation state is said to have undergone oxidation and labeled as the reducing agent. Complex redox reactions, involving three or more chemicals are the basis for fireworks. The beautiful colors produced are a result of emission of light by electronic transitions within different transition metals found in the compounds used.

Resources:

• Core Reactions III: Redox PowerPoint slides about the different definitions of reduction and oxidation.

Discrepant Event

In the video below, IB Diploma students in one of my former schools and myself are playing with fire crackers and making observations in an effort to understand the chemistry of fire crackers. Watch the video to see what they do and the various different demonstrations performed.

And the questions are (and the first questions also appear in my MYP and IGCSE Chemistry Discrepant Event of the same name):

1. Find some firecracker ingredients and their reactions. Balance them.
2. Find out about the energetics of the reactions.
3. Using one of the various methods available, in terms of redox, identify the reducing agent(s) and oxidizing agent(s).
4. What do you notice about the products of a reaction in a fire cracker?
5. Using your answer to questions 2 and 3, suggest a reason fire crackers produce a loud bang?
6. In the demonstration towards the end of the video, a fire cracker was set off under an inverted tin can. Why did the can fly up into the air?
7. Suggest variables which might affect the loudness of the bang and the height to which the can flies. Design an investigation to study one of the variables and its effect either on the loudness of the bang or the height to which the can flies. In your design, describe what data would be collected and how they would be analyzed to determine the composition that produces the best results.

Concepts involved:

• reduction, oxidation, reducing agent, oxidizing agent.
• chemical equation, chemical reaction, mole ratio, stoichiometric ratio.
• Enthalpy, expansion, gas laws, entropy, rate of reaction.

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