Lab Notes - August 31st - Nitric Acid from Calcium Nitrate and My Hotplate Failed, Again.

Some lab notes for the month of august 2020

I was exploring more nitric acid and wanted to see if calcium nitrate and sodium bisulfate would be viable. The rationale is that the reaction of calcium nitrate and sulfuric acid is well-known but almost never done directly since it produces insoluble calcium sulphate that solidifies into a rock in the flask. It has to be drilled out and risks break the flask. The traditional way to use calcium nitrate is the "wet process" where we first mix it with water and then add sulfuric acid. The calcium sulfate precipitates out and the dilute nitric acid is filtered and purified by distillation. This is slow and laborious so i was wondering if sodium bisulfate could be advantageous in producing a residue that didn't need to be drilled. This would save time and less risk of breaking glassware.

So i mixed 49g of calcium ammonium nitrate decahydrate with 150g of sodium bisulfate monohydrate and heated it directly in the "dry process" of making nitric acid. Nitric acid was distilled over and the yield was 85%. But more importantly the solid residue of sodium sulfate, sodium bisulfate and calcium sulfate was soluble. Upon addition of water it dissolved into a slurry that could easily be poured out. So i think the process is superior to using sulfuric acid as there is overall less labor involved.

For thoroughness i also tried the wet process by first dissolving the calcium nitrate in 50mL of water and adding sodium bisulfate. After distillation the yield was 95% but with 50mL of extra water diluting it. Personally i prefer higher concentration acid and don't mind the lower yields of the dry process.

Anyway. I was going to do additional nitric acid experiments but my hotplate failed.

Turns out the temperature sensor failed open and the safety limit of the hotplate refused to turn it on. It was a simple matter of finding the broken sensor and replacing it. The interesting note is that the hotplate uses a PT1000 RTD and it seemed the original was spot welded in. I didn't have spot welding capability so i used copper foil to crimp the connection.

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