Sciencemadness Discussion Board

Ferric Chloride impurities

CHRIS25 - 10-2-2013 at 04:34

Having looked at many threads and images of ferric chloride I have come to the conclusion that my final product is probably a mixture of oxide complex and ferric chloride. It was a very dark purple black just before the final drying out process. It is now a 'darkish' orange brown solid more orange than brown. Confident that there is no Hydroxide (too acidic before drying), and that purple black is a pure hexahydrate I was wondering whether I have drawn the correct conclusions?
I forgot to remark that although there could be ferrous chloride mixed in I actually do not see how this is possible, I went to great lengths to ensure that all the ferrous was converted to ferric and also ensured that the final solution just before evaporation was as concentrated as possible, I removed as much water as was possible with magnesium sulphate and then gently heated the finale phase to dryness (hexahydrate hopefully), this took literally 30 minutes for about 50mLs.

[Edited on 10-2-2013 by CHRIS25]

weiming1998 - 10-2-2013 at 06:16

You cannot heat ferric chloride to dryness. Like aluminium chloride or copper (II) nitrate, it will decompose no matter how gentle you heat it (at ordinary pressure). The only way to obtain crystals is by slow evaporation (in a dessicator bag if the air is too humid). Some of the FeCl3.6H2O will also first liquefy when heated, which makes it appear like there is still liquid water in the product. Further heating yields a mixture of steam and HCl, leaving behind oxides and oxychlorides and destroying your product.

To get it back again, just redissolve your resulting dry solid back in concentrated HCl, gently heat it for a while, then evaporate the slow way.

CHRIS25 - 10-2-2013 at 12:17

Quote: Originally posted by weiming1998  
You cannot heat ferric chloride to dryness. Like aluminium chloride or copper (II) nitrate, it will decompose no matter how gentle you heat it (at ordinary pressure). The only way to obtain crystals is by slow evaporation (in a dessicator bag if the air is too humid). Some of the FeCl3.6H2O will also first liquefy when heated, which makes it appear like there is still liquid water in the product. Further heating yields a mixture of steam and HCl, leaving behind oxides and oxychlorides and destroying your product.

To get it back again, just redissolve your resulting dry solid back in concentrated HCl, gently heat it for a while, then evaporate the slow way.

oh...agh...ok thanks.