At the equivalence point,moles(acid) = moles(base)which means thatmolarity(acid) × volume(acid) = molarity(base) × volume(base)The moment when exactly enough base has been added to the sample to
neutralize the acid present is called the equivalence point. In the lab, an indicator
is used to tell when the equivalence point has been reached. An indicator is a
substance that is one color in acid solution and a different color in basic solution.
Two popular indicators are phenolphthalein, which is clear in acidic solution
and pink in basic solution; and litmus, which is pink in acidic solution and blue
in basic solution.
Identifying Chemicals
Precipitation—Unknown ions in solution can be identified by precipitation. If
you know which salts are soluble and which are insoluble, you can use
process of elimination to identify unknown ions in solution. For instance,
nearly all salts containing chlorine are soluble, but silver chloride is not; if
you put chloride ions into a solution and a precipitate is formed, silver ions
were probably present in the solution.
Conduction—You can tell whether a solution contains ions or not by checking
to see if the solution conducts electricity. Ionic solutes conduct electricity
in solution; nonionic solutes do not.
Flame Tests—Certain chemicals burn with distinctly colored flames. This is
especially true of the alkali metals and the alkaline earth metals. It’s a good
idea to know which colors salts of certain metals burn.
Red Lithium, Strontium
OrangeCalcium
YellowSodium
Green Barium
Violet Potassium