The Amateur Chemist

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How to make 68% azeotropic nitric acid


Ingredients

222.78 grams Calcium Ammonium Nitrate
108 grams 98% Sulfuric Acid
94.4 grams water

Procedure

This method of making nitric acid is by far my favorite. It makes around 200 ml of 68% to 70% nitric acid. This concentration of acid is much easier to store and can by used for pretty much every application. All of the chemicals are easy to get and the distillation is fairly quick. Calcium Ammonium Nitrate (CAN) can be bought very cheaply on ebay as 'calcinit'. It is advertised as calcium nitrate but is really CAN. I can get 5 pounds for around $15. 

2 [5Ca(NO3)2 . NH4NO3 .10H2O] + 11H2SO4 --> 22HNO3 + 10[CaSO4 . 2H2O] + (NH4)2SO4 + 8H2O


Basically...

Add the CAN to the flask with a funnel. Add all of the water to the flask, then slowly add the acid to flask. Stir well as it might start to decompose. As you stir, it will form some sort of cottage cheese like compound. This is normal. Put the distillation apparatus together and turn the water on. Slowly heat the flask up to 121 degrees Celcius. Pure nitric acid distills at around 87 celcius, but at 68% it forms an azeotrope with water that distills at a higher temperature. It will collect weak nitric acid from 90 to 121 degrees celcius. Save this, then switch collecting flasks when the temp. gets to 121. Go to you have collected around 200 ml of acid. 


You can distill to it is pretty dry without worrying about your flask cracking. It is also pretty easy stuff to clean out too. Just pour some water in and shake. There shouldn't be too much decomposition, but if there is, then just turn the temp. down a bit. If you want stronger acid, then you can combine it with an equal amount of concentrated sulfuric acid and distill off. The sulfuric acid will break the azeotrope in the nitric acid and absorb the water.