How to Make Anhydrous Ferrous Chloride

While there are multiple tutorials for Ferric Chloride on Instructables, Ferrous chloride is something different. Ferrous Chloride is an ionic solid with the chemical formula FeCl2, where the iron ion has a 2+ charge. Ferric Chloride is similar, but has iron ions with 3+ charge, giving it the formula FeCl3. Production of Ferrous chloride is rather easy in theory, just add hydrochloric (muratic) acid (HCl) to metallic iron (Fe). In practice, however, it is more difficult, since exposure to oxygen in the air oxidizes Ferrous Chloride to unwanted Ferric Chloride, and the anhydrous form of the chloride will also pull moisture from the air, creating the green tetrahydrate (For more chemical information click here). To get our white anhydrous Ferrous Chloride then, we must react and dry our product in a relatively closed container, so that oxygen and water from the air cannot interfere. The main purpose I had for making this compound is that it is a useful precursor to true ferrofluid, the kind that is not just iron filings in vegetable oil, but an actual near-homogenous liquid, and I plan on making a separate Instructable for that eventually using the product from this reaction.

Reactants:

• 310g (~270mL) of 31.45% (10M) Hydrochloric Acid
• >50g Iron Metal (Steel works, but not stainless steel, because it contains chromium and other unwanted metals)
• Optional - a few grams of sodium carbonate (Washing soda) or sodium bicarbonate (Baking soda)

Tools and Labware:

• Erlenmeyer flask (500ml) with stopper & output tube or some alternate sealed, heat resistant container with a output tube
• Output tube
• 2x Open-topped container (for bubbler and filtration)
• Scale with accuracy within 1g
• Hot plate (stirrer optional)
• Funnel with filter paper
• Optional - Magnetic stir bar, if hot plate has a stirring function

============WARNING============

This reaction releases large quantities of hydrochloric acid vapor, which is harmful if inhaled, and extremely corrosive to exposed metals. Do this outside or in an extremely well ventilated area, such as a fume hood.

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Using the scale, mass out about 50g of iron metal. This can come from steel wool, nails, iron shavings, as long as it is only iron or steel. Set this aside for now. Place the Erlenmeyer flask on the scale now and zero it. Add to this the hydrochloric acid until the scale reads 310g, or you have added 270mL of the acid. You may place the flask on the hot plate, although is not necessary and will only speed up the reaction. Connect the tube to the stopper and make sure it can reach a nearby container which will be used for the bubbler. To this bubbler, add the baking soda, if being used, and then add at least 100mL of water to dissolve the soda. you can now add the iron metal to the flask and add the stopper, making sure the only way in/out of the flask is through the tube. In my case, I used a custom PVC stopper and some clay to make sure that it was sealed, since the flask did not have standardized joints. Turn on the hotplate to a relatively low setting if it is being used, as the goal is to heat the reaction, but not boil it. The reaction tends to be exothermic, meaning it releases heat, so constant heating may not be necessary.

It may take a few hours to a few days, depending on if the flask was heated, but eventually the iron should entirely dissolve, or there will appear to be no bubbling but there is still iron metal. If there is a large amount of iron remaining, try adding more acid, as a large amount may have vaporized and left the flask leaving less to react. If there is no immediate reaction, try heating up the solution. If you have noticed that the flask has cooled down and a green crystalline solid has formed, that is a good sign. It means the reaction has nearly or fully completed and you can move to the next step. Filter the solution through the funnel into a second container and add the filtrate back into the flask. If all the iron is gone, add a few grams more in large pieces, as you will still need some metallic iron for the next step.

Place the Erlenmeyer flask back on the hot plate, and turn on the hotplate so that the solution begins boiling. Any crystals that have formed will begin dissolving from a higher solubility. the stopper may also be removed while the solution is boiling, since enough gas is being released that it prevents air from getting in the flask. It should be added back when the solid has begun to form. The goal is to boil the solution until it becomes a green solid, then dry it until it becomes a white or off-white solid. From experience, this process must be closely watched as it tended to try to boil over on multiple occasions. The mess that forms, of Ferric and Ferrous Chlorides and Oxides is not easy nor fun to clean, so be careful. After the white solid has been made, completely seal the flask and let it cool.

Since anhydrous Ferrous Chloride is both oxygen sensitive and moisture sensitive, it must be stored in an unreactive, sealed, dry container. To get it out of the flask, since it is likely all in one chunk, it should be relatively easy to shake the flask, breaking up the chunks. when transferring this, you may still need to use pliers or some other tool to break the chunks into small enough pieces to fit through the neck. Something like a glass canning jar or lab chemical container is idea for storing your finished product, The expected mass of the chloride is around 145 grams, but this may vary depending on lab practices and the specific procedure. I got a very low yield due to multiple overflows and relatively poor lab practices (I rather despise working with iron compounds). You will want to store your container of Ferrous Chloride in a cool dry place until use, and only open when necessary, to reduce atmospheric exposure.