Actually normality depends upon a simple formula that is :-

Normality = Number of Gram equivalents / litre

The term gram equivalents change as the valency of a substance changes . all the elements do not have same valence and hence it varies from element to element or molecule to molecule.

And the term gram equivalents is calculated as follows

Number of gram equivalents = molar mass/ valency

Number of gram equivalents = molar mass/ number of electrons exchanged.

To explain it further lets take examples of two elements and two molecules.

Eq mass of oxygen = molar mass/valency

                                                = 16/2

                                                = 8

Eq. mass of florine = molar mass/ valency

                                                = 18 / 1

                                                = 18

Eq. mass of NaCl = molar mass / number of electrons exchanged

NaCl → Na+ + Cl   (one electron exchanged )

Eq. mass of NaCl= 23+35.5

                                    = 58.5

Similarly eq. mass of H2SO4  = 2+32+64 / 2

H2SO4  → 2H+ + SO42-    (2 electrons exchanged)

Eq.mass of H2SO4  = 98/2

                                    = 49

Now lets see the normality

For 1 normal solution of NaCl we will do the following calculation:-

1 n solution of NaCl Will be = 1 gram equivalents / 1000ml

So we will have = 58g / 1000 ml      (or 1 L)

Now for 1 normal H2SO4  :-

For 1 Normal solution of  H2SO4  = 1 gram equivalent / 1000ml

                                                                        = 49/1000ml

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