Question

describe normality , strength of solution.

Answer 1

Normality: There is a relationship between normality and molarity. Normality can only be calculated when we deal with reactions, because normality is a function of equivalents.

The example below uses potassium hydroxide (KOH) to neutralize arsenic acid. By studying the reaction it is possible to determine the proton exchange number to determine the normality of the arsenic acid.

Look at the equation H3AsO4 + 2KOH --> K2HAsO4 + 2H2O:

Equivalent weight = molar mass/(H+ per mole)

Equivalent = mass of compound / Equivalent weight

And Normality = (equivalents of X)/Liter

And the part that is of interest to you is that Normality = molarity x n (where n = the number of protons exchanged in a reaction).

You probably remember that when a hydrogen atom is ionized and loses its electron, you are left with only a proton. So a hydrogen ion is basically a proton.

Let's assume that we have a 0.25 M solution of H3AsO4 and want to determine the normality of it if it participates in the reaction

H3AsO4 + 2KOH --> K2HAsO4 + 2H2O

When H3AsO4 is neutralized by KOH, H3AsO4 provides two protons to form 2H2O.

Note that H3AsO4 has three hydrogens, but K2HAsO4 only has one hydrogen. That means that 2 protons were exchanged,

Again normality = molarity * n

Remember that normality of the solution is 0.25 mol H3AsO4 and there were two protons exchanged (2 equivalents/mole)

Answer 2

Strength of a solution is defined as the amount of the solute in gms, present in one litre of the solution. It is expressed as gL-1.
 normality of a solution is defined as the molar concentration ci divided by an equivalence factor feq: