After making sulfuric acid by diaphragm electrolysis more than a year ago, I've had a few requests to try making nitric acid by the same process, and have decided to give it a go in this video.

By electrolysing a solution of potassium nitrate, we slowly generate nitric acid on the anode, as a result of the electrostatic attraction between the anode and the nitrate ion, and the formation of hydrogen ions on the anode surface. Using a semi-permeable diaphragm between the two electrodes, we can isolate the nitric acid we generate, and collect it after running the cell for a day or two.

Sadly, testing the current setup for this length of time only yields about 250mL of nitric acid at a very low concentration (0.7M at best), which is not particularly useful when compared with the concentrated stuff, in fact, to dissolve copper metal I first had to concentrate the acid by a factor of 3.

In order to be a viable production method, some changes must be made to the process. Possibly, changing the volumes of the chambers, lengthening the run time, or adding a second diaphragm to prevent the reduction of nitrate ions on the cathode may improve the yield, but maybe I'll try that in another video.