Background
Reaction amongst the three ingredients of gunpowder is a little more complex of a redox reaction than the ones you will have studied in class. The stoichiometric quantities of substances involved is considerably large as you will notice once you find a balanced equation for the process. However, the process involved is the same. One or more substances undergo reduction while one or more undergo oxidation. And, not unlike many other redox reactions, it is highly energetic.
Resources:
- M5 Stoichiometry III: Chemical Reaction & Reaction Stoichiometry: Descriptions of what chemical equations and reactions are and the information furnished by them!
- M5 Stoichiometry IV: Mass Relationships: Descriptions of how chemicals in a reaction are related to one another quantitatively.
- M4 Fuels and Energy: This page contains links to two PowerPoint slides: one on Energy Changes and the other on Fuels and Energy.
- M5 Redox I: Definitions: Definitions of Redox Reactions.
- M5 Redox II: Oxidation State: Description of oxidation state and how it can be used to identify redox reactions.
Discrepant Event
Gunpowder ingredients are readily available in a secondary school laboratory. Not only that, gunpowder can be made and safely set off in the safety of a secondary school laboratory.
The video below is that of six different compositions of the ingredients set off in a fume hood. The girls were competing against the boys. The reaction in this instance was initiated by using a fuse made of filter paper soaked in concentrated solution of potassium nitrate and dried. Watch the movie for the results.
Here are the questions:
- What are the ingredients of gunpowder? (There are three.)
- There are two chemical reactions taking place in the process. The first one is the one taking place on the fuse and the other between the ingredients of gunpowder. Can you suggest chemical equations for those two reactions? Balance the equations.
- Both the reactions are redox reactions. Identify the oxidizing and reducing agents in each of the reactions.
- What was the competition? In other words, what was the criteria on which their mixture was being judged?
- What factors affect the duration for which the flame lasts and the height of the flame? In other words, what determines the efficiency of the reaction? How could you determine the duration of the reaction and the height of the flame using the video?
- What other measurements could be made to determine the relative efficiency of the reaction of the different mixtures?
- If you had to prepare a 10.0g mixture of the ingredients so that it produced as high a flame as possible, what would be the composition?
- If you had to prepare a 10.0g mixture so that it burned for as long as possible, releasing energy steadily, what would be the composition?
Concepts involved:
- reduction, oxidation, complete combustion, incomplete combustion, rate of reaction, oxidizing agent, reducing agent.
- stoichiometry, molar ratio, stoichiometric ratio, limiting regent, excess reagent.
