In each reaction, indicate whether oxidation or reduction is occuring.

Question

N₂ → NH₃

CH₂CH₃OHCH₃ → CH₃COCH₃

Zn → Zn²⁺ + 2e^-

HCHO → HCOOH

A. reduction

B. oxidation

Answer 1

First, understand the definition of oxidation reactions and reduction reactions. A helpful acronym is 'OIL RIG.'

In oxidation reactions, there is a 'loss of electrons' (Oxidation Is Loss = OIL) in the form of bonds. So, there is a decrease in bonds with Hydrogen (or C - H bonds decrease) and an increase in bonds with Electronegative atoms (or C - Z bonds increase, where Z is an electronegative atom).

(Hydrogens share electrons, so a decrease in bonds with Hydrogen = to loss of electrons. Also, electronegative atoms pull electron density towards itself, which = to loss of electrons).

In reduction reactions, there is a 'gain of electrons' (Reduction Is Gain = RIG) in the form of bonds. So there is an increase in bonds with Hydrogen (or C - H bonds increase) and a decrease in bonds with Electronegative atoms (or C - Z bonds decrease).

Now apply these criteria to your question. For added help, sketch out the bonds between each atom:

N₂ → NH₃

_{Here, you are removing 3 bonds with nitrogen (reactant side), and instead replacing it with 3 Hydrogen bonds (product side) = Reduction}

CH₂CH₃OHCH₃ → CH₃COCH₃

_{Here, you are removing 3 hydrogen bonds with carbon, removing 1 hydrogen bond with oxygen (reactant side), and instead increasing the number of bonds between oxygen and carbon (product side) = Oxidation}

Zn → Zn²⁺ + 2e^-

^{Here, Zn (reactant side) is losing 2 electrons (product side) = Oxidation}

HCHO → HCOOH

_{Here, an aldehyde (reactant side) becomes a carboxylic acid (product side). On the products side, there is a bond added between C and an O = Oxidation}