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# FeSO4 solution mixed with (NH4)2SO4 solution in 1:1 molar ratio gives the test of Fe2+ ion but CuSO4solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu2+ ion. Explain why? - CBSE (Science) Class 12 - Chemistry

ConceptWerner’S Theory of Coordination Compounds

#### Question

FeSO4 solution mixed with (NH4)2SO4 solution in 1:1 molar ratio gives the test of Fe2+ ion but CuSO4solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu2+ ion. Explain why?

#### Solution

(NH_4)_2SO_4+FeSO_4+6H_2O -> FeSO_4.(NH_4)_2SO_4.6H_2O

Mohr's salt

CuSO_4 + 4NH_3 + 5H_2O ->[Cu(NH_3)_4]SO_4.5H_2O

tetraamminocopper(ii) sulphate

Both the compounds i.e.,FeSO_4.(NH_4)_2SO_4.6H_2O and CuSO_4 + 4NH_3 + 5H_2O 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 but that which breaks up into its constituent ions in the dissolved state. These compounds exhibit individual properties of their constituents. For e.g. FeSO_4.(NH_4)_2SO_4.6H_2O  breaks into Fe2+, NH4+, and SO42− 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 lost. This happens because [Cu(NH_3)_4]SO_4 .5H_2O] does not show the test for Cu2+. The ions present in the solution of [Cu(NH_3)_4]SO_4.5H_2O are [Cu(NH_3)_4)]^(2+) and SO_4^(2-).

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#### APPEARS IN

NCERT Solution for Chemistry Textbook for Class 12 (2018 to Current)
Chapter 9: Coordinate Compounds
Q: 2 | Page no. 258

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Solution FeSO4 solution mixed with (NH4)2SO4 solution in 1:1 molar ratio gives the test of Fe2+ ion but CuSO4solution mixed with aqueous ammonia in 1:4 molar ratio does not give the test of Cu2+ ion. Explain why? Concept: Werner’S Theory of Coordination Compounds.
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