NORMALITY

Useful unit of concentration in quantitative analysis is normality (N), a one normal solution contain one equivalent per liter.

An equivalent represents the mass of material providing avogadro’s number of reacting units. A reacting unit is a proton (in acid-base reaction) or an electron (in oxidation-reduction reaction). The normality of solution is calculated from:

The advantage of expressing concentration in normality and quantities as equivalent is that one equivalent of substance A will Always react with one equivalent of substance B. For the example one equivalent of KOH(=1 mol) will react with one equivalent of HNO3 (=1mol) or with one equivalent of H2SO4 (1/2 mol)

It useful to recognize that, since :

meq A = meq B

Once can calculate the volume of two solutions that will react by :

Na x mLA = NB x mLB

Example 1

Calculate the normality of the solution containing 14.205 g/L of Na2SO4 ( When SO42- reacts with two protons).

Solution

SO42- reacts with 2H+ to form H2SO4

Mol Na2SO4 per L
= 14.205 / 142.05
= 0.1 mol

Number of equivalents Na2SO4
= 0.1 x 2
= 0.2 eq

Normality = 0.2 eq / 1 L = 0.2 N