Equivalent weight acid base

Equivalent Weights Acid-base titrations can be used to characterize the chemical and physical properties of matter. One simple example is the determination of the equivalent weighf of acids and bases. In this method, an accurately weighed sample of a pure acid or base is titrated to a well-defined equivalence point using a mono-protic strong acid or strong base. If we assume that the titration involves the transfer of n protons, then the moles of titrant needed to reach the equivalence point is given as... 

Eor phosphoric acid, the number of equivalents is the number of Fi ions donated to the base. Eor the reactions in (a), (b), and (c) the number of equivalents are 3, 2, and 1, respectively. Thus, the calculated equivalent weights and normalities are... 

Two useful characterization applications involving acid-base titrimetry are the determination of equivalent weight, and the determination of acid-base dissociation constants. 

An acid-base titration can be used to determine an analyte s equivalent weight, but cannot be used to determine its formula weight. Explain why. 

EXAMPLE 15.12. A new solid acid was prepared in a laboratory its formula weight was not known. It was titrated with standard base, and the number of moles of base was calculated. Without knowing the formula of the acid, can you tell how many moles of the acid was present in a certain mass of acid Can you tell how many equivalents of acid was present ... 

A sample of 4.00 g of a solid acid was treated with 50.00 mL of 2.000 V NaOH, which dissolved it completely (by reacting with it). There was enough excess NaOH to require 10.07 mL of 1.000 N HC1 to neutralize the excess base. What is the equivalent weight of the acid ... 

For example, if there are 2.0 equivalents dissolved per liter, a solution would be referred to as 2.0 normal, or 2.0 N. The equivalent is either the same as the mole or some fraction of the mole, depending on the reaction involved, and the equivalent weight, or the weight of one equivalent, is either the same as the formula weight or some fraction of the formula weight. Normality is either the same as molarity or some multiple of molarity. Let us illustrate with acids and bases in acid-base neutralization reactions. 

The equivalent weight of an acid in an acid-base neutralization reaction is defined as the formula weight divided by the number of hydrogens lost per formula of the acid in the reaction. Acids may lose one or more hydrogens (per formula) when reacting with a base. 

As in Section 4.3, acid-base neutralization reactions will be illustrated here. In order to calculate the equivalent weight of an acid, the balanced equation representing the reaction in which the solution is to be used is needed so that the number of hydrogens lost per formula in the reaction can be determined. The equivalent weight of an acid is the formula weight of the acid divided by the number of hydrogens lost per molecule (see Section 4.3). 

Thus a one-to-one reaction is involved, and in fact, all reactions of EDTA with metal ions (most metals do react with EDTA) are one-to-one. Therefore, we will not be concerned with a formal scheme for determining equivalent weights, as we were with acid-base reactions. 

Written in this form, you see that the equivalents (or milliequivalents) of acid are equal to the equivalents of base. The equivalent weight of the acid is the grams of acid divided by the equivalents of base. The equivalent weight of monoprotic acid is equal to the molecular weight. The equivalent weight of diprotic acid is equal to half the molecular weight. 

Potassium hydrogen phthalate has many uses in analytical chemistry. It is a primary standard for standardization of bases in aqueous solutions. Its equivalent weight is 204.2. It also is a primary standard for acids in anhydrous acetic acid. Other applications are as a buffer in pH determinations and as a reference standard for chemical oxygen demand (COD). The theoretical COD of a Img/L potassium hydrogen phthalate is 1.176mg O2. 

Carboxylic acids dissolve in Na,CO, thereby evolving CO,. The neutralization equivalent or equivalent weight of a carboxylic acid is determined by titration with standard base it is the number of grams of acid neutralized by one equivalent of base. If 40.00 mL of a O.IOON base is needed to... 

The volume of base (0.1696L) multiplied by the normality of the base (I.OOOeq/L) gives 0.1696 as the number of equivalents of acid titrated. Since the weight of acid is 10.0 g. one equivalent of acid weighs... 

The acid-base equivalent is defined as the weight (in grams) ef a substance that will provide, react with, or be equivalent to 1 mole of H+. us 1 mo e (98.1 g/mole) of H2S04 contains 2 moles ofH+ and its acid"base equivalent weight is... 

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