Expert: Dr. Henry Boyter, Jr. - 9/20/2008

Question
I have always thought the titration equation is M1V1=M2V2, however, a question I recently answered changed my point of view. It says that:

What volume of 0.4M Ba(OH)2 is needed to exactly neutralize 100ml of 0.2M HBr? The answer is 25ml.

So I began to think, is the titration equation correct in the above form or should it be "coefficient of A * Ma * Va = coefficient of B* Mb * Vb"? Please help

Answer
First M1V1 = M2V2 is really the dilution equation for making solutions.  It can also be used for simple acid/base titrations, but the form is MaVa = MbVb, but the a is H+ and the b is OH-.  It is not the concentration and volume of the compound used.  In the example you gave it would be:

(0.2)(100) = (0.8)(x)  0.8 is the concentration of OH-

You have written another form of the equation that does allow you to use the compound concentrations, but I find students mess it up.  You will soon learn in class what "equivalents" are and that will take care of the whole situation.