Redox reaction of sugar in our cells generates the energy necessary for our bodies. The reaction can be easily conducted using a standard oxidizing agent and an initiator.
The video below is that of six different mixtures of sugar and an oxidizing agent prepared by a class of former students in one of my former school. The girls were competing against the boys. The reaction in this instance was initiated by adding a drop of concentrated sulfuric acid. Watch the movie for the results.
Here are the questions:
- There are two chemical reactions taking place in the process. The first one involves the initiator concentrated sulfuric acid and sugar and the other between the oxidizing agent and suger. Can you suggest chemical equations for those reactions?
- Identify the oxidizing and reducing agents in the reaction.
- What was the criterion on which the mixture were being judged? Can you think of other ways of judging the reaction? (Some fuels generate little energy but slowly for a long period of time, while another might generate a lot of energy for a short period of time. Some fuels still might produce a lot of by products which may or may not be useful or harmful, while other might not leave behind much. Each fuel has its own use.)
- What’s the stoichiometric ratio of chemicals involved in the reaction? What would determine how you would adjust the ratio if you were to conduct the reaction?
- What quantitative measurements could be made to determine the relative efficiency of the oxidation of the different mixtures?
- If you had to prepare a 5.0g mixture of the oxidizing agent and sugar so that it produced energy as slowly as possible BUT left as little solid by products as possible, what would be the composition? What measurements would you make to judge the mixture’s success?
- Find out how much energy a mole of sugar produces when it undergoes complete combustion. Determine how much energy would produced in theory by your mixture.
- Design an investigation that studies the relationship between the ratio of the two ingredients and one of the following factors:
- flame size (height?)
- duration for which the mixture burns
- efficiency of the reaction
- (or one of your choosing)
In your design, also indicate how you would analyze the data to determine the experimental ratio that produces the best results.
Concepts involved:
- reduction, oxidation, complete combustion, incomplete combustion, dehydration, rate of reaction, oxidizing agent, reducing agent.
- stoichiometry, moles, molar ratio, stoichiometric ratio, limiting regent, excess reagent.
- energetics, enthalpy of combustion.
