Colour changes, investigation

NOTE. It is not expected that a student xvill attempt to memorise all the colour tests given in Part III. He might for example be expected to know the Phthalein Reaction for phenol itself (p. 339). Details of the divergence from the standard result are recorded primarily for reference, so that a student will not be diverted from his line of investigation if he observes that a suspected phenol does not respond exactly to the standard colour changes. 

Because the reaction involves a colour change, you can determine the concentration of Fe(SCN) (aq) by measuring the intensity of the colour. You will find out how to do this in Investigation 7-A. For now, assume that it can be done. From the measurements of colour intensity, you can calculate the equilibrium concentration of Fe(SCN) (aq). Then, knowing the initial concentration of each solution, you can calculate the equilibrium concentration of each ion using the chemical equation. 

In this investigation, you will use Le Chatelier s principle to predict the effect of changing one factor in each system at equilibrium. Then you will test your prediction using a colour change or the appearance (or disappearance) of a precipitate. 

The reactions of alcohols related to phenolphthalein and fluorescein with Ag1 ions have been investigated for their application as colorimetric reagents in determining trace amounts of silver. A simple, rapid and sensitive method was found which used 2,4,5,7-tetra-bromofluorescein and 1,10-phenanthroline. A ternary complex was formed with a deep pink colour (Ama 550 nm) in the presence of silver(I) ions and the two reagents. No significant colour change was observed in the absence of the diimine.227... 

Distibanes and dibismuthanes have received most of the attention with respect to colour changes. Diarsanes do not show similar phenomena but have been investigated for a better... 

Substituted ferrocenes display a markedly increased photosensitivity l.l -dibenzoylferrocene decomposes or shows colour changes on irradiation in alcohols, ethers, esters, acetone, acetonitrile, pyridine, dimethylsulfoxide etc. 501>. The products of these reactions have not been investigated. 

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