Synthesis and isolation of barium chloride

This is not a real experiment, but a description of how to make pure barium chloride 2-hydrate from cheap potteries grade barium carbonate. From 1 gram of potteries barium carbonate also 1 gram of pure barium chloride 2-hydrate can be obtained. This synthesis can be done easily with batches of 10 to 50 grams of barium carbonate. Less than 10 grams is not recommended, because mechanical losses will become relatively large when small quantities are used. More than 50 grams per batch may be impractical for many people, because it requires the use of big beakers.

The procedure given below requires some patience, but it is not hard to do nor does it require a lot of effort. Most of the time you have to wait for evaporation of a liquid or settling of a fine precipitate. The final result is a snow-white material which gives a clear solution in distilled water and which shows a pure green flame color, free of sodium ions. The resulting chemical can be used for experiments or used as a starting point for making other barium compounds, such as barium bromate or barium iodate.

 

Required chemicals:

  • barium carbonate, cheap potteries grade

  • hydrochloric acid, 10%

  • distilled water

  • hydrogen peroxide, 3%

Required equipment:

  • glass beakers

  • evaporating dish

  • long tall bottle or set of test tubes

  • syringe with thin flexible tube attached, or a pipette

  • filter paper and funnel (preferably, but not required)

  • if no pure hydrochloric acid is available, an acid-resistant distillation setup is required as well

Safety:

  • Barium compounds are toxic, avoid inhalation of dust or fine aerosols, containing barium salts.

  • Potteries grade (cheap) barium carbonate also contains a few percents of barium sulfide, which gives very toxic and very smelly hydrogen sulfide when it is dissolved in hydrochloric acid.

  • Hydrochloric acid at a concentration of 10% is moderately corrosive. If this comes in contact with the skin, then rinse with some water.

Disposal:

  • A small amount of waste is produced. For each 10 grams of barium carbonate used approximately 1 gram of barium-containing waste is produced. If only a few grams of barium chloride is prepared, then this waste can be flushed down the drain, but if larger quantities are processed, then it is best to bring the waste to a proper processing facility.

 

 

 
 

 

Step 1: Dissolving of the material in dilute hydrochloric acid

In this step, the barium carbonate is dissolved in dilute hydrochloric acid and prepared for the second step of the synthesis. This first step can best be done outside, because of formation of a toxic aerosol and because of formation of toxic and smelly hydrogen sulfide.

Put the barium carbonate in a glass beaker. When 10 gram is used, take a 100 ml beaker, when 25 gram is used, take a 250 ml beaker and when 50 gram is used, take a 500 ml beaker.

For each gram of barium carbonate take 5 ml of distilled water. Add the water to the solid barium carbonate and swirl the beaker, such that a slurry of barium carbonate in water is formed. Assure that no dry clumps of barium carbonate are left in the water. With a plastic or glass rod break apart any clumps of dry powder which are not yet wetted.

For each gram of barium carbonate take 4 ml of 10% hydrochloric acid. This is a slight excess amount. The acid must be a good quality acid, it must be colorless and free of dissolved non-volatile impurities. Good colorless acid can easily be made from impure material with a glass distillation setup (see below).

Slowly pour the acid in the suspension of barium carbonate in water. Do not add too much acid at once, because the liquid strongly froths when acid is added. Swirl the beaker after each addition of acid until fizzling stops. Then add the next portion of acid. Do this outside or in a fume hood. Besides carbon dioxide also some hydrogen sulfide is formed, because of the sulfide content of the cheap potteries grade barium carbonate. Due to the strong bubbling also many small droplets of liquid are sprayed around. For this reason it is best to do this step outside. Stop adding acid when the liquid is not completely turbid anymore or until 4 ml of acid is added for each gram of barium carbonate. You will not obtain a completely clear liquid, it remains opalescent even if a large excess amount of acid is added. So, as soon as the liquid becomes opalescent instead of milky-white, no more acid needs to be added.

To the opalescent liquid add a few ml of 3% hydrogen peroxide. This destroys most of the sulfide in the liquid and makes it less smelly. Heat the liquid for a while in order to make solid matter somewhat more coarse and for destroying excess hydrogen peroxide. During this heating a bad sulphur-like smell is produced, so it is best to do this outside, but if this is done inside, then assure that the room is well-ventilated. The addition of the hydrogen peroxide also may make the liquid more turbid, but that does not matter.

 

Step 2: Filtering of the opalescent liquid

After performing step 1 you have an opalescent or turbid liquid, which also has a somewhat sulphur-like smell. There also may be more coarse grains of solid material in this liquid. Potteries grade barium carbonate contains a lot of insoluble crud and this needs to be filtered.

If you have real filter paper, then use that for filtering the solution. Use the finest paper you have. Do not use a coffee-filter, because that introduces new impurities and it also is too coarse for filtering the liquid. A coffee-filter also is quite large and a lot of liquid is absorbed by the filter, leading to excessive loss.

If no suitable filtering equipment is available, then pour the liquid in a long tall bottle, or pour it in a set of long test tubes which are filled to 2 cm below the rim. Let the liquid stand in the bottle or the vertical test tubes for two days, allowing the solid matter to settle at the bottom. With a pipette or a syringe, to which a thin flexible tube is attached, the liquid then can be taken away from the bottle or test tubes and transferred to another flask. Leave the last cm or so. You can pour the last amounts in a test tube again and wait another 2 days to retrieve most of the clear liquid from that as well. Of course you can also accept the 10% loss if you do not want to wait another 2 days for just 10% of such cheap starting chemicals.

 

Step 3: First drying stage, making of crude barium chloride

The liquid, obtained after step 2 is almost clear and can be used for making crude barium chloride. In this step, the barium chloride is dried, but at the same time, aerial oxidation of remains of sulfide allow the formation of sulphur and/or insoluble barium sulfate, which then can be separated in step 4.

Put the liquid in a dish and allow the liquid to evaporate on a warm and dry place. Keep in mind that the liquid has a fairly strong sulphur-like smell which can cause discomfort for some people. Use adequate ventilation in the room where the liquid is allowed to evaporate.

If a layer of 4 to 5 mm of liquid is poured in a sufficiently large dish, then it takes around 1 day to get dry material. This dry material is crude barium chloride, which does not give a clear solution. While the liquid is allowed to evaporate it becomes turbid again and pale yellow material settles at the bottom. For this reason the result of the first evaporation is not really pure.

After performing step 3, for each gram of barium carbonate you will have around 1.1 gram of crude barium chloride.

 

Step 4: Separating insoluble matter from the crude barium chloride

The dry material from step 3 contains insoluble matter (mostly sulphur and barium sulfate) and it is not yet suitable for most aqueous chemistry experiments. In this step, it is redissolved in order to get rid of the insoluble impurities.

For each gram of barium carbonate, taken in step 1, take 5 ml of distilled water. Add the solid material to the distilled water and swirl until all of the solid material has dissolved. The resulting liquid at least is opalescent, but it might even be completely turbid.

Pour the liquid in a tall bottle or a set of test tubes which are placed in a purely vertical position. If test tubes are used, then cover them with a piece of paper, such that no dust can get into them. Allow the liquid to stand for at least 24 hours, 48 hours is even better.

When all solid material has settled at the bottom, then with a pipette or syringe to which a thin flexible tube is attached, carefully take away liquid from the bottle or test tubes. Be sure not to draw solid material into the pipette or syringe. If test tubes or long/narrow flasks are used, then better than 90% recovery of liquid is possible without sucking solid matter into the pipette or syringe.

 

Step 5: Final evaporation and drying of the barium chloride

In this step the now clear liquid is allowed to evaporate and pure and very clean barium chloride is made. The liquid now is totally odorless.

Do as in step 3, pour the liquid in a clean evaporating dish and place this in a warm and dry place. In 24 to 48 hours a snow-white crystalline solid is obtained.

Scrape the solid from the evaporating dish and crush the largest crystals. Spread the solid mass over a glass plate or a large petri dish and allow drying of the solid on a warm heating radiator for a few hours. This results in a perfectly dry and snow-white glittering solid.

The still warm solid quickly must be transferred to a vial which must be tightly closed. Barium chloride is somewhat hygroscopic, so do not leave the dry solid in contact with cold air if you want to keep it nicely dry.

Final yield is approximately 1 gram of barium chloride 2-hydrate per gram of barium carbonate. This is a yield of 80% of theory (assuming 100% pure barium carbonate).

 

Discussion of this synthesis

Potteries grade barium carbonate is very impure material. In practice, only around 95% really is barium carbonate, the remaining 5% mostly is barium sulfide, but it may also contain some barium sulfate, barium oxide and insoluble sand-like material. Potteries grade barium carbonate usually does not contain sodium salts (flame color of barium carbonate is nice green and is not overwhelmed by the intense orange flame color of sodium) and the amount of heavy metal salts also can be neglected (which is important for potteries processes, because most heavy metals give strong color to ceramics).

When the material is dissolved in dilute hydrochloric acid, then barium chloride is formed, which goes into solution. The barium sulfide impurity leads to formation of hydrogen sulfide, which gives a strong smell of rotten eggs to the bubbles of gas. The barium sulfide also leads to opalescence of the solution, because part of the sulfide is oxidized by oxygen from the air to sulphur which does not dissolve. Barium sulfate, present in the barium carbonate also leads to opalescence. Use of hydrogen peroxide makes the solution somewhat less smelly, because hydrogen sulfide is oxidized to sulphur and water.

    main/intended reaction: BaCO3 + 2H+ → Ba2+ + H2O + CO2

    reaction of main impurity: BaS + 2H+ → Ba2+ + H2S

    aerial oxidation: 2H2S + O2 → 2[S] + 2H2O            8[S]  → S8 (very fine solid material)

In step 3, the first drying stage, the liquid becomes more and more turbid, while it is standing in the evaporation dish. This is because this liquid still contains quite some sulfide, which slowly is oxidized by air according to the above reaction equation, while it is standing in the evaporation dish. The presence of this sulfide also explains the bad smell of the liquid.

In step 5 there is no odor anymore. All sulfide has been oxidized in step 3 and no smelly material is left after step 4. The final result is a pure and clean snow-white product.

 

Main losses are due to filtering, or because a thin layer of liquid is discarded because it cannot easily be separated from the precipitated solid matter.

 

Making pure hydrochloric acid, suitable for the synthesis of barium chloride

If no colorless hydrochloric acid is available, but only the yellow/green material from a hardware store, then this can be prepared from the impure acid easily by distillation. This distillation can best be done in an all-glass apparatus with ground joints. If no such apparatus is available, then one can use glass flaks and tubes, connected to each other with teflon tape. Do not use metal flasks or plastic/rubber for the distillation and collection of the hot hydrochloric acid.

If 30% acid is used as a starting point, then dilute this acid by taking 1 volume of water and 2 volumes of acid. Mix these two liquids and then distill from an all-glass apparatus. Distill 250 ml of this liquid and keep on distilling until only 50 ml is left. Discard the last 50 ml. The 200 ml of liquid which came over into the distilling flask is very pure colorless hydrochloric acid of approximately 20% concentration and if any impurity is left, then it is volatile and does not harm in the synthesis of barium chloride. This can be diluted with an equal volume of distilled water for making just over 10% acid.

If 10% acid is used as a starting point, then distill 500 ml of acid in an all glass apparatus. First, the temperature of the boiling liquid will be around 100 ºC and almost pure water comes over. Discard this liquid. At a certain point, the temperature will rise to 108 ºC fairly quickly. If it goes through 105 ºC then collect the liquid and keep on distilling until only 50 ml of liquid is left. This gives around 200 ml of 15% to 20% pure hydrochloric acid containing no or only volatile impurities. The precise concentration of the acid is hard to tell without titration, but for the synthesis of the barium chloride it is OK to dilute 3 volumes of this acid with 2 volumes of distilled water and use that in the procedure, given above.

 
   

 

   

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