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How to Calculate an Equivalence Reagent Table

A large quantity of chemical laboratory work involves titrations of acids and bases. It is important to know the concentrations of the acids and bases used in the titrations so you can determine the amount of unknown present in a sample. Molarity is one way of expressing concentrations, which tells you how many moles of the acid or base are present in the solution. An alternate way to express concentration is Normality. Normality expresses the amount of acid or base present in the solution. In many cases, the value of Molarity and Normality are the same, but in the situation where you are using an acid or base that can provide more than one hydrogen ion or hydroxide ion, the values are different.

Instructions

- 1
  Draw a table on your paper that has four columns across the top of the paper and as many rows as you have reagents. Label the first column Reagent Name. Continue labeling columns across the page with Formula, Molarity, equivalence/mole and Normality.
- 2
  Fill in the name and chemical formula of each of the reagents used in the reaction in the first two columns. Use one row per chemical.
- 3
  Write the concentration of each of the solutions in Molarity units into the third column. The information to fill in the first three columns is on the labels of the bottle in the laboratory.
- 4
  Determine how many equivalents you get for each mole of acid or base. For example, the following four chemicals illustrate the concept of equivalents: HCl, NaOH, H3PO4 and Mg(OH)2. When each of these chemicals dissolves in water, you will have either a predominant amount of hydrogen ion or a predominant amount of hydroxide ion. For HCl you get a single hydrogen ion and for NaOH you release a single hydroxide ion. Phosphoric acid, H3PO4, is a triprotic acid that releases three hydrogen ions per mole of acid. Mg(OH)2 is possesses two hydroxide ions that are released upon dissolution in water, which represents 2 equivalents per mole. Therefore, HCl and NaOH both have 1 equivalent per mole and H3PO4 has 3 equivalents per mole.
- 5
  Fill in the fourth column with the number of equivalents per mole of chemical.
- 6
  Calculate the Normality of each of the chemicals in the table and complete the entries in the table. The Normality is equal to the molarity multiplied by the equivalents per mole. For example, a 1 Molar solution of H2SO4 is diprotic and has 2 equivalents per mole. The Normality = molarity x equivalence = 1.0 x 2 = 2.0 Normal.

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