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In coordination chemistry, a stability constant (also called formation constant or binding constant) is an equilibrium constant for the formation of a complex in solution. It is a measure of the strength of the interaction between the reagents that come together to form the complex. There are two main kinds of complex: compounds formed by the ...
Thiocyanate complexes are not widely used commercially. Possibly the oldest application of thiocyanate complexes was the use of thiocyanate as a test for ferric ions in aqueous solution. [14] The reverse was also used: testing for the presence of thiocyanate by the addition of ferric salts. The 1:1 complex of thiocyanate and iron is deeply red.
For example, it will react with diluted sulfuric acid under heating forming potassium sulfate, ferric sulfate and hydrogen cyanide. 2 K 3 [Fe(CN) 6] + 6 H 2 SO 4 → 3 K 2 SO 4 + Fe 2 (SO 4) 3 + 12 HCN. This won't occour with concentrated sulfuric acid as hydrolysis to formic acid and dehydration to carbon monoxide will take place instead. [17]
An example of a low-spin iron(III) complex is [Fe(CN) 6] 3−. The cyanide ligands may easily be detached in [Fe(CN) 6 ] 3− , and hence this complex is poisonous, unlike the iron(II) complex [Fe(CN) 6 ] 4− found in Prussian blue, [ 16 ] which does not release hydrogen cyanide except when dilute acids are added. [ 17 ]
The complex has O h symmetry. The iron is low spin and easily reduced to the related ferrocyanide ion [Fe(CN) 6] 4−, which is a ferrous (Fe 2+) derivative. This redox couple is reversible and entails no making or breaking of Fe–C bonds: [Fe(CN) 6] 3− + e − ⇌ [Fe(CN) 6] 4−. This redox couple is a standard in electrochemistry.
This is a list of unsolved problems in chemistry. Problems in chemistry are considered unsolved when an expert in the field considers it unsolved or when several experts in the field disagree about a solution to a problem.
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It can be painted onto a surface or kept as a colorless solution. When in contact with ferric chloride solution (or other solutions containing Fe 3+), the product of the reaction is a solution with a blood red colour, due to the formation of the thiocyanatoiron complex ion. Thus this chemical is often used to create the effect of 'stigmata'.