Most technical grade H2SO4 solutions are contaminated with additional dyes and metal ions, either from the industrial synthesis process or by the chemical addition by the companies(such as dyes).
All grades can be purified by adding a small amount of H2O2(preferably 30-35%) to oxidize the ions in the solution reducing the pigment color. H2SO4 in a pure state is an almost water-clear color. H2O2 does this beautifully with the addition of heat to provide some activation energy to get the rxn going.
Prepare your H2SO4 solution. I used the glass apparatus below. It's a 500ml FB attached to a stoppered 105 vac. adapter with heavy walled tubing attached at the nipple leading outdoors.
Pour your H2SO4 into the flask and add the H2O2. The molar ratio of H2SO4:H2O2 should be 1:1/50. This can be scaled up or down relatively easily. Pretty much a capful of 35% H2O2 will clear up most of the color of 1000ml con. H2SO4. Feel free to experiment with ratios as they aren't really important. I have tested this and excess is much better than too little, the only thing is the more H2O2 you add the more you'll have to boil off.
Anyways, heat this up. BEWARE as the H2SO4 will release colorless choking odors so make sure you're doing this outside or venting outside(I did all this in my lab
).
This is where paths diverge. Some brands are very dark. Some are less so. Mine was a light yellow-orange as seen in the pic below. Typically the darker your H2SO4 is the more the impurities will foam up. Mine hardly foamed as you can see in the pics below...and when it did it was white, innocent looking bubbles.
You'll know the rxn is complete when as your adding heat the bubbles start to form(effervesce), and then more, and MORE, and then finally the foam comes roaring to the top, and then it settles down(all while the heat is still going), and finally dies...lastly, let the whole flask cool down and you're done.
Your purified H2SO4 should be relatively free of color. Mine was a nearly 100% crystal clear. Many thanks to Sedit for the original idea that inspired this writeup.
-PStain.
All grades can be purified by adding a small amount of H2O2(preferably 30-35%) to oxidize the ions in the solution reducing the pigment color. H2SO4 in a pure state is an almost water-clear color. H2O2 does this beautifully with the addition of heat to provide some activation energy to get the rxn going.
Prepare your H2SO4 solution. I used the glass apparatus below. It's a 500ml FB attached to a stoppered 105 vac. adapter with heavy walled tubing attached at the nipple leading outdoors.
Pour your H2SO4 into the flask and add the H2O2. The molar ratio of H2SO4:H2O2 should be 1:1/50. This can be scaled up or down relatively easily. Pretty much a capful of 35% H2O2 will clear up most of the color of 1000ml con. H2SO4. Feel free to experiment with ratios as they aren't really important. I have tested this and excess is much better than too little, the only thing is the more H2O2 you add the more you'll have to boil off.
Anyways, heat this up. BEWARE as the H2SO4 will release colorless choking odors so make sure you're doing this outside or venting outside(I did all this in my lab
). This is where paths diverge. Some brands are very dark. Some are less so. Mine was a light yellow-orange as seen in the pic below. Typically the darker your H2SO4 is the more the impurities will foam up. Mine hardly foamed as you can see in the pics below...and when it did it was white, innocent looking bubbles.
You'll know the rxn is complete when as your adding heat the bubbles start to form(effervesce), and then more, and MORE, and then finally the foam comes roaring to the top, and then it settles down(all while the heat is still going), and finally dies...lastly, let the whole flask cool down and you're done.
Your purified H2SO4 should be relatively free of color. Mine was a nearly 100% crystal clear. Many thanks to Sedit for the original idea that inspired this writeup.
-PStain.
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