Question

Sol. SO₃​ exists in three allotropic forms.

a) α−SO₃​: It is chemially active form. It forms long transparent ice like crystals. The melting point of this form is 17oC.

b) β−SO₃​: It is dimeric (S₂​O₆​). It forms needle like silky white crystals. It melts at 32.5oC. Above 50oC, it changes to α-form.

c) It is like β-form and is obtained by completely drying β−SO₃​. It melts at 62.2oC under 2 atmospheric pressure.