This lab was pretty simple, and was really just an excuse to burn more magnesium ribbon.  We followed Ian Guch’s Energy Diagram Lab in 24 Lessons That Rocked the World. Students took an approximately 4cm long piece of magnesium ribbon, found its mass on the small pocket scale (it was too small for the triple beam balance) and then calculated how many moles of magnesium they had.

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Mg ribbon in crucible over butane burner… never ignited.

The lab says to put the ribbon in a crucible and place it over a bunsen burner.  We don’t have bunsen burners so we put it over a butane burner and even opening it up all the way we could not get the magnesium ribbon to burn, so we ended up holding it with tongs directly in the flame. This very clearly showed the reaction had a high activation energy.

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Student holding burning Mg ribbon with tongs.

We can’t really measure the energy given off in the reaction but we can calculate it.  The energy that would be released when they burned the ribbon is the amount of Mg they burned in moles (which was very small, like 0.004 moles) multiplied by the heat of reaction which is given in the lab in kJ/mole.

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Energy Diagram from Ian Guch’s 24 Lessons That Rocked the World

Students then sketched an energy diagram, showing that the products (MgO) have less energy than the reactants (Mg and O2) because its exothermic and it has a high activation energy (had to put it directly in the flame to ignite it). The lab had a worksheet at the end that the students worked on it in class since the lab was so short.

Students were asked to watch Crash Course Chemistry #32 Kinetics before class.

 

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