The Foundations of Chemistry

_?_ g (COOH) 2 0.003550 mol NaOH

0.1598 g (COOH) 2

The 0.1743-g sample contained 0.1598 g of (COOH) 2 , so its percentage purity was

% purity100% 91.68% pure (COOH) 2

You should now work Exercise 36.

EQUIVALENT WEIGHTS AND NORMALITY

Because one mole of an acid does not necessarily neutralize one mole of a base, some
chemists prefer a method of expressing concentration other than molarity to retain a one-
to-one relationship. Concentrations of solutions of acids and bases are frequently expressed
as normality(N). The normalityof a solution is defined as the number of equivalent
weights, or simply equivalents (eq), of solute per liter of solution. Normality may be repre-
sented symbolically as

Normality

By definition there are 1000 milliequivalent weights (meq) in one equivalent weight of
an acid or base. Normality may also be represented as

Normality

In acid–base reactions, one equivalent weight,or equivalent (eq), of an acidis
defined as the mass of the acid (expressed in grams) that could furnish 6.022 1023
hydrogen ions (1 mol) or that could react with 6.022 1023 hydroxide ions (1 mol). One
mole of an acid contains 6.022 1023 formula units of the acid. Consider hydrochloric
acid as a typical monoprotic acid.

H 2 O

HCl 8888n H
(aq) 
 Cl(aq)

1 mol 1 mol 1 mol

36.46 g 1.008 g 35.45 g

6.022 1023 6.022 1023 6.022 1023

formula units formula units formula units

We see that one mole of HCl can produce 6.022 1023 H
ions, and so one mole of HCl
is one equivalent.The same is true for all monoprotic acids.

no. meq



mL

number of milliequivalent weights of solute



milliliter of solution

no. eq



L

number of equivalent weights of solute



liter of solution

11-4

0.1598 g (COOH) 2



0.1743 g sample

90.04 g (COOH) 2



1 mol (COOH) 2

1 mol (COOH) 2



2 mol NaOH

Any calculation that can be carried out

with equivalent weights and normality

can also be done by the mole method

using molarity. The methods of this

section are widely used, however, in

health-related fields and in many

industrial laboratories.

An equivalent weightis often referred

to simply as an equivalent(eq).

11-4 Equivalent Weights and Normality 411

A milliequivalent weightis often

referred to simply as a milliequivalent

(meq).