Equivalent Masses of Acids and Bases

The quotient of the gram formula mass of an acid by the number of hydrogen atoms which are replaceable for the reaction under consideration is called the equivalent mass of the acid. Likewise, the quotient of the gram formula mass of a base by the number of hydroxyl groups which are replaceable for the reaction under consideration is called the equivalent mass of the base. 

One equivalent mass of an acid neutralizes one equivalent mass of a base. It is important to note that the equivalent mass of a polyprotic acid is not invariant for H3PO4 it may be the gram formula mass, one half this, or one third, depending on whether one, two, or three hydrogens are effective in the reaction under consideration. 

The normality of a solution of an acid or base is the number of equivalents of acid or base per liter a 1 N solution contains 1 equivalent per liter of solution. By determining, with use of an indicator such as litmus. 

Example 12-3. It is found by experiment that 25.0 ml of a solution of sodium hydroxide is neutralized by 20.0 ml of a 0.100 N acid solution. What are the normality of the alkaline solution and the mass of NaOH per liter  

Solution. The unknown normality x of the alkaline solution is found by solving the equation that expresses the equivalence of the portions of the two solutions  

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