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Ferrous chloride synthesis procedure

Posted by aonomus on March 6, 2010


This document outlines the synthesis of the air sensitive compound ferrous chloride tetrahydrate using non air-free technique. Ferrous chloride can be used as a source for iron(II), as a oxygen scavenger, reducing agent, and precursor to magnetite.

Materials and Apparatus

Chemicals & Materials

  • Ferric chloride hexahydrate
  • Distilled water
  • Hydrochloric acid
  • Iron metal or 0000 mesh (ultra fine) steel wool)


  • Hot plate/magnetic stirrer with oil bath
  • 3 neck 500mL round bottom flask (and 2 stoppers) and a 1 neck 500mL round bottom flask
  • 105degree 3 way distillation adapter, Liebig condenser, vacuum distillation 105 degree adapter
  • Vacuum filtration flask, buchner funnel, filter paper and diatomaceous earth
  • Mortar and pestle, beaker
  • Labelled storage bottle with tight seal and parafilm
  • Teflon coated magnetic stir bar


Preface notes:

This procedure is qualitative, you can scale the values to whatever is needed. Additionally it is not quantitative in that some iron (II) will be oxidized to iron (III) over a period of time.

  1. Begin by dissolving ferric chloride hexahydrate in 300mL distilled water in the 500mL round bottom flask, as much as would be required to stoichiometrically give your minimum desired yield of ferrous chloride tetrahydrate.
  2. Acidify with 1-3mL concentrated hydrochloric acid. This acid provides extra chloride ions for any ferrous chloride that becomes oxidized to ferric chloride (without additional chloride ions available, iron(III) oxide/hydroxides would result.
  3. Add balls of super-fine steel wool to the round bottom flask until they occupy approximately 1/4 to 1/2 the volume of the flask. This is so that the reaction can proceed faster with a greater surface area, and less carbon (steel wool is a iron-carbon alloy, where carbon is non reactive with this solution and remains as a thin sediment in the solution).
  4. Warm the solution with stirring using the hot plate and oil bath, effervescence may be observed. Continue stirring and adding iron or steel wool until the solution is a strong green colour. Remove from heat
  5. Clamp vacuum filtration flask to a stand and set up the buchner funnel with a piece of filter paper, then a layer of diatomaceous earth. Filter the solution by suction as many times as necessary until the filtrate is a clear green solution. Clean the 3 neck flask, add the ferrous chloride solution to the flask.
  6. Set up the distillation apparatus with the 1 neck 500mL flask as the reciever. Begin distillation and proceed until the solution is too thick for the magnetic stirrer to properly stir, and where bumping occurs.
  7. Remove from heat and apply vacuum to assist in more removal of water, then seal the flask. This step is important as it helps purge oxygen from atmosphere inside, and replace it with water vapor. As the slurry cools, ferrous chloride crystallizes in the remaining water and forms a hard cake at the bottom of the flask.
  8. After cooling to room temperature, the ferrous chloride is now ready to be recovered. Carefully take a spatula and a hard object, and through each of the 3 necks, chip apart the cake of ferrous chloride and continually remove chunks into a temporary container (beaker). Work fast, as air exposure will oxidize ferrous chloride to mixed ferric chloride/oxides/hydroxides.
  9. After all the ferrous chloride has been removed, process the ferrous chloride and store. Pre-weigh your storage container (ensure at this time that it seals tightly and that you have tape or parafilm handy). Take portions of the ferrous chloride and grind them to a fine powder and add them to the bottle until all your ferrous chloride is in the bottle. Record your yield and note on the label, including time of preparation. Replace cover tightly and seal with parafilm or tape.

Closing remarks

  • This procedure is a relatively complex one and relies on using water vapour and vacuum to displace most of the oxygen in a closed system and gives satisfactory results. Failure to exclude oxygen properly will result in spoilage of the product, even over storage.
  • Oxidized product can be re-reduced using the same procedure, however the reaction is slow because the mixed oxides/chlorides are poorly soluble. Also, effervescence is observed as the reduction proceeds to completion. During this re-reduction process, more iron is added, so the total product amount will be somewhat greater than the original (pre oxidized) amount.

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