Oxidation - Any process in which the oxidation number of an atom increases (becomes more positive).

Reduction - Any process in which the oxidation number of an atom decreases (becomes more negative).

Oxidation Number - The charge that an atom would have if the compound in which it were found were ionic.

Redox Reaction (oxidation-reduction reaction) - A reaction in which at least one atom changes in oxidation state.

LEO goes GER

• Losing Electrons is Oxidation

• Gaining Electrons is Reduction

1) A metal reacts with a strong oxyacid to yield an oxidized metal, a reduced gas, and water

NOTE:  Since these reactions are with a strong acid, we usually only need to worry about the H⁺ ion.  Generally, the anion in the acid acts only as a spectator ion in these reactions, so it can be disregarded.  In order to have H atoms on both sides of the reaction, H₂O is added as a product.

• A piece of copper metal is immersed in dilute nitric acid.

• A strip of copper is added to concentrated sulfuric acid.

• Silver metal is added to a nitric acid solution.

2) Redox with Dichromate (Cr₂O₇)

NOTE:  When it is noted that the solution is acidified, then it is important to include H⁺ as a reactant.  In order to have H atoms on both sides of the reaction, H₂O is added as a product.

• Potassium dichromate solution is added to an acidified solution of iron(II) chloride.
  • To balance the reduction of the Cr⁶⁺ in the dichromate ion to Cr³⁺, the iron ion must undergo oxidation.

• A solution of potassium iodide is mixed with an acidified potassium dichromate solution.
  • To balance the reduction of the Cr⁶⁺ in the dichromate ion to Cr³⁺, the iodide ion must be undergo oxidation.

• Solid sodium dichromate is added to an acidified solution of sodium iodide.
  • To balance the reduction of the Cr⁶⁺ in the dichromate ion to Cr³⁺, the iodide ion must be undergo oxidation.
  • NOTE:  The reaction says SOLID sodium dichromate, so the reactant cannot be written as its respective ions.

3) Redox with Permanganate (MnO₄)

NOTE:  When it is noted that the solution is acidified, then it is important to include H⁺ as a reactant.  In order to have H atoms on both sides of the reaction, H₂O is added as a product.

• Solid potassium permanganate is added to concentrated hydrochloric acid.
  • To balance the reduction of Mn⁷⁺ to Mn²⁺, the chloride ion must undergo oxidation.
  • NOTE:  The reaction says SOLID potassium permanganate, so the reactant cannot be written as its respective ions.

• A solution of potassium permanganate is added to an acidified solution of hydrogen peroxide.
  • To balance the reduction of Mn⁷⁺ to Mn²⁺, the oxygen in the hydrogen peroxide must undergo oxidation.

• A solution of tin(II) chloride is added to an acidified solution of potassium permanganate.
  • To balance the reduction of Mn⁷⁺ to Mn²⁺, the tin ion must undergo oxidation.

Next:  "Overview of Organic Reactions"