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April 2019 Limerick Project

Redox Reactions

“The ‘oil rig,’ a helpful mnemonic
For redox’s challenges chronic.
Mind errors, potential.
This note is essential:
View of loss/gain must be electron-ic.”

The 7 April 2019 limerick addresses another reaction classification topic, this time looking at “reduction-oxidation” chemistry. Reduction and oxidation are themselves names that correspond to specific processes; they always happen in tandem, so the chemical shorthand becomes “Red-Ox,” or “redox.” Redox is a term that can apply to a wide range of subclasses of reactions; combustion (from the 6 April 2019 limerick) is one of these.  

In particular, the poem clarifies the use of a common memory trick for describing redox processes. The discussion focuses on the most obvious type of redox reaction, a displacement reaction, to keep the discussion as straightforward as possible.

“The “oil rig,” a helpful mnemonic/
For redox’s challenges chronic.”
Redox reactions involve electron movement.  Because electrons are negatively charged, the elements to which and from which electrons flow experience a change in their own charges over the course of the reaction.  These can be challenging reactions to consider, as redox concepts can manifest themselves in several ways.    

In the simplified reaction below, the notation used for the reactants (left of the arrow) shows us that Element A starts out as a neutral metal and Element B starts out with a positive charge, in their reactant forms.  In their product forms (right of the arrow), Element A has a positive charge and Element B is a neutral metal. 

This is also called a displacement reaction because A “displaces” B in terms of forming a compound with C.  

A + BC → B + AC   

The “mnemonic” in question links the movement of electrons to the chemical vocabulary: “Oxidation Is Loss; Reduction Is Gain.”  This statement is abbreviated as “OIL RIG.”

In the reaction above, Element A is oxidized, losing electrons to go from neutral to positively charged; Element B is reduced; gaining electrons to go from positively charged to neutral.   

“Mind errors, potential./ This note is essential:/
View of loss/gain must be electron-ic.”
A common error with these reactions is viewing “loss” and “gain” in terms of the values of the charges on the elements, neglecting the fact that electrons are negatively charged.  (In the example above, the ERROR would be saying: A’s charge becomes more positive; thus, it “gains”; thus, it is reduced.)

The application of the “oil rig” mnemonic relies on considering loss/gain in terms of electrons.