Simulation · Chemistry · Class 12
How many chlorides can silver find?
From the lesson Werner's theory in Coordination Compounds. Change the values and watch what happens.
The idea behind it
NCERT §5.1
- A coordination compound holds a central metal atom or ion joined to a set of anions or neutral molecules through shared electron pairs. Chlorophyll (Mg), haemoglobin (Fe) and vitamin B12 (Co) are all coordination compounds.
- Werner tested the cobalt(III) chloride-ammonia compounds with excess cold AgNO₃. Per mole: CoCl₃·6NH₃ (yellow) gave 3 mol AgCl, CoCl₃·5NH₃ (purple) gave 2, and both forms of CoCl₃·4NH₃ (green and violet) gave 1.
- He explained this by keeping six groups (Cl⁻, NH₃ or both) fixed on the cobalt in a unit that does not break up: [Co(NH₃)₆]Cl₃ is a 1:3 electrolyte, [CoCl(NH₃)₅]Cl₂ a 1:2 electrolyte and [CoCl₂(NH₃)₄]Cl a 1:1 electrolyte, as their conductivities confirm.
- Only chloride outside the square bracket is free to meet Ag⁺; chloride bonded to the metal inside the bracket is not precipitated.
- The green and violet CoCl₃·4NH₃ share one empirical formula but differ in properties, so they are isomers.
- Werner's postulates (1898): a metal shows primary and secondary valences. Primary valences are ionisable and satisfied by negative ions. Secondary valences are non-ionisable, satisfied by neutral molecules or anions, equal to the coordination number and fixed for a given metal.
- The groups held by secondary valences have a definite arrangement in space for each coordination number, today called the coordination polyhedron. The bracketed species is the complex; ions outside are counter ions.
- Common shapes: [Co(NH₃)₆]³⁺, [CoCl(NH₃)₅]²⁺ and [CoCl₂(NH₃)₄]⁺ are octahedral, [Ni(CO)₄] is tetrahedral and [PtCl₄]²⁻ is square planar.
- A double salt such as carnallite (KCl·MgCl₂·6H₂O), Mohr's salt (FeSO₄·(NH₄)₂SO₄·6H₂O) or potash alum breaks up completely into simple ions in water. A complex does not: K₄[Fe(CN)₆] gives [Fe(CN)₆]⁴⁻, not Fe²⁺ and CN⁻.
More simulations in Coordination Compounds
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