Test: Werner's Theory of Coordination Compounds & Some important definitions (December 24) - NEET MCQ

The different compounds of cobalt(III) chloride with ammonia show distinct properties, most notably with respect to colour and conductivity measurements in solution.

In coordination compounds, the ions outside the square brackets are called counter ions, and the species within the square bracket are the coordination entities.

Werner observed that ‘x’ mol of AgCl was precipitated per mole of CoCl₃.4NH₃ with excess silver nitrate. Currently, there are seven groups attached to the cobalt atom. For the secondary valence to be six, one of the chloride (x=1) has to be precipitated as AgCl, therefore 1:1 electrolyte.

After the reaction, it will form [Ni(H₂O)₆]^2- and 2Cl^– in which the former is the coordination complex. There are six water molecules bound to Ni, which makes the secondary valence of Ni as 6.

Since the secondary valence is 6, the compound should have six groups linked to Pt atom. But it already has six groups linked to it and cannot lose any Cl atoms to form AgCl. Hence, no AgCl will be produced.

In [Co(H₂O)(CN)(en)₂]²⁺, the overall charge is +2 and 0, -1, and 0 on H2O, CN, and en groups respectively. If ‘x’ is the oxidation number of Co, then (x + 0 – 1 + 0 = +2), which implies x=+3. Similarly, in [CoBr₂(en)₂]⁺, the charge on Br is -1, so if ‘y’ is the oxidation number of Co, then (y – 2 + 0 = +1), which implies y=+3. Therefore, the sum of the oxidation numbers is 3 + 3 = 6.

It is given that 3 parts of the platinum chloride compounds in excess silver nitrate gives 9 parts of AgCl and 3 parts of the complex ion. There are two approaches to this: Method 1 (By balancing): It is seen that (3 x 4 = 12) atoms of Cl on the left give (9 x 1 = 9) on the right, which leaves 3 Cl atoms, that is one in each complex ion. Now, each complex ion has 1 Cl and 5 NH3 linked to Pt, giving a secondary valence of 6. Method 2 (By proportioning): 3 mols gives 9 mols, which implies, 1 part of compound will give 3 parts of AgCl. Thus, only one Cl atom remains with the compound along with 5 NH3 molecules, giving Pt a secondary valence of 6.