How do you identifying redox, precipitate, and acid base reactions?

1 Answer
Dec 1, 2016

These are usually identified by experience.


Redox reactions involve a formal change in oxidation number. The combustion of hydrocarbons is certainly an oxidation reaction, as carbon, in the hydrocarbon, is oxidized to #CO_2#, in which carbon has a formal oxidation number of #C(+IV)#. For every oxidation, which is formally a loss of electrons, there is a corresponding reduction, a gain in electrons:

#C^(0)(s) + O""_2^(0)(g) rarr C^(+IV)O""_2^(-II)(g)#

Here, dixoygen gas (a very common oxidant) is reduced to oxide anion; i.e. each oxygen atom has gained 2 electrons. The source of the electrons is of course the carbon atom, which has formally lost 4 electrons, and is oxidized up to #C(+IV)#.

Precipitation reactions typically involve the precipitation of an insoluble precipitate. Ions in solution can form insoluble compounds, and precipitate (i.e. deposit) out of solution. Inorganic chemistry is rich in precipitation reactions:

#Ag^(+) + Cl^(-) rarr AgCl(s)darr#

Such precipitation reactions can be used to effect separations in mixtures, by precipitating out insoluble salts.

And acid-base reactions are reactions which are typically conducted in water. The characteristic cation of the solution, the acid, which is water we may represent as #"hydronium ion, "H_3O^+#, reacts with the characteristic anion of the solution, the base, which in water we represent as #"hydroxide ion, "HO^-#, to form water:

#HO^(-) + H_3O^(+) rightleftharpoons2H_2O(l)#

Other solvents, and other acid-base reactions exist. The most common one is liquid ammonia, i.e.:

#2NH_3(l) rightleftharpoonsNH_4^(+) + H_2N^(-)#.

Clearly, you will have to read your text to consolidate your understanding.