Q. Show Experimental observations of werners theory?
Werner showed that his postulates are consistent with experimental observations. He made use of basically three kinds of experiments to justify his conclu8ions. Let us look at some of these experiments.
It is well known fact that weaker base in a compound is replaced on reacting with a stronger base. For example, ammonia is released from ammonium salts h) reaction with a strong base like NaOH. However, when a complex containing ammonia molecules like [co(NH3)6]+3 is treated with NaOH, no ammonia is released. It is not released even on treatment with strong acids under mild conditions. A reasonable conclusion would be that the ammonia molecules are bound in a different manner to the metal ion.
The qualitative and quantitative presence of halogen in ionic form can be established by treating the compound with silver nitqte, which would give a precipitate of silver chloride. or example, a compound with a composition CoCl3 -5NH3 on treatment with AgN03 gives two mole AgCl precipitate per mole of the compound. From this observation the obvious conclusion is that one chlorine is bound to metal in a different way from the other two.
Measurement of molar conductance of a salt solution of approximately 10-3M concentration can tell us the number of ions present in solution. For instance a molar conductance value of around 520 ohm-1 mol-1 cm2 indicates the presence of five ions in solution whereas values around 400,230 and I00 ohm-1mol-1cm2 indicate 4.3 and 2 ions respectively. Werner analysed a series of platinum arnmine complexes and arrived at correct formulation in each case on the basis of molar conductance measurements.
Wemer argued that since the secondary valencies have a definite orientation in space, complexes should show stereoisomerism the case of a six coordinated complex three geometrical shapes are possible namely. Planar prismatic or octahedral.