Question

FeSO₄ solution mixed with (NH₄)₂SO₄ solution in 1:1 molar ratio gives the test of Fe²⁺ ion but CuSO₄ solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu²⁺ ion. Explain why?

Answer 1

Both compounds i.e. FeSO₄ (NH₄)₂SO₄.6H₂O and [Cu(NH₃)₄]SO₄.5H₂O fall under the category of addition compounds with only one major difference i.e. the former is an example of a double salt, while the latter is a coordination compound. A double salt is an addition compound that is stable in the solid state bnK that which breaks up into its constituent ions in the dissolved state. These compounds exhibit individual properties of their constituents for e.g. FeSO₄ (NH₄)₂SO₄.6H₂O breaks into Fe²⁺ NH₄⁺, and SO₄^2- ions. Hence, it gives a positive test for Fe²⁺ ions. A coordination compound is an addition compound which retains its identity In the solid as well as in the dissolved state. However, the individual properties of the constituents are cost. This happens because [Cu(NH₃)]₄]SO₄.5H₂O does not show the test for Cu²⁺ The ions present in the solution of [Cu(NH₃)₄]SO₄.5H₂O are [Cu(NH₃)₄]²⁺ and SO₄^2-