Question

How to calculate the equivalent weight of al2(so4)3

Answer 1

Normality:

It is defined as the number of gram -equivalents of solute dissolved in one liter of solution. and designated by symbol 'N'

Normality (N) = Gram equivalent of solute / Volume of solution in liter
where, Gram equivalent is the ratio of weight of the compound to equivalent weight of the compound

Equivalent weight is Molecular weight / Z
Z is a number whose value depends on the chemical context of reaction
For salts: Z is the oxidation or valence state of the ion.
Al2(SO4)3 :
molecular weight of Al2(SO4)3 : 2 X 27 + 3 X 32 + 2X 16 =342
for Al2(SO4)3, Z=6 because 2Al+3 is equivalent to 6 moles of H+.
valence of Al2(SO4)3: 6

equivalent weight of Al2(SO4)3 : 342 / 6 = 57

1 mole Al2(SO4)3 is 342 gm

Normality of 1 mole al sulph is

57 gm eq valent / lit is 1 N solution

342 gm / lit therefore is 6 N solution

The answer is 6 N

Answer 2

 In Inorganic compounds like these, finding Equivalent weight is simple.

The total positive charge is given by 2Al³⁺ = 6
The total negative charge is given by 3SO₄⁻² = 6

The total positive charge = the total negative charge = n-factor = 6

And we know,                                  
                                                          molecular weight
                        equivalent weight =  -------------------------
                                                              n- factor