Question

Why is removal of borate and phosphates essential in inorganic qualitative analysis?

Answer 1

Explanation: Borates and phosphates are known as interfering anions as they interfere during the analysis of cations present after Group II-B.

Their removal is necessary if one needs to test cations present from Group III onward.

Reason for removal of Borate ions: They form insoluble salts with cations of Group III, IV and V.

$Fe^{3+}+BO_3^{3-}\rightarrow FeBO_3$        (Cation of Group III)

$3Zn^{2+}+2BO_3^{3-}\rightarrow Zn_3(BO_3)_2$ (Cation of Group IV)

$3Ca^{2+}+2BO_3^{3-}\rightarrow Ca_3(BO_3)_2$ (Cation of group V)

Reason for removal of Phosphate ions: They also form insoluble salts with cations of Group III,IV and V.

$Fe^{3+}+PO_4^{3-}\rightarrow FePO_4$       (Cation of Group III)

$3Zn^{2+}+2PO_4^{3-}\rightarrow Zn_3(PO_4)_2$ (Cation of Group IV)

$3Ca^{2+}+2PO_4^{3-}\rightarrow Ca_3(PO_4)_2$ (Cation of group V)

These anions should be removed from the solution as they either form precipitates or form stable complexes with the cations because in either case, the cation is removed from the solution and is unavailable for further analysis.

For correct analysis of cations, these interfering anions should be removed from the solution.