This is a lab which deals with oxidation-reduction. We did a set of experiments in the lab. This is our procedure and observations:
a) Dissolve a small amount of magnesium (II) chloride in half a beaker of water. (There is no redox process yet). Now add a few mL of NaOH. First make observations before the solution is stirred, then stir only briefly. Watch for change particularly on the liquid surface. (hint: the first fluffy precipitate observed is not a result of redox, rather it is a result of precipitation (solubility of hydroxides))
observation: It turns yellow, and a solid type is formed and settles on the bottom. Once stirred, it got a bit darker. Solid is formed and is more noticeable. Black precipitate forms in the top of the solution.
b) Add a small amount of MnO2 to 6M HCl.
Observation: When 6M HCl was added to MnO2, it just turned into a dark solution and it looks like MnO2 is not dissolved.
This solution explains how to propose a redox reaction based on experimental data of:
1) Reaction of magnesium chloride and sodium hydroxide.
2) Reaction of manganese (IV) oxide and hydrochloric acid.