ignilc

I'm electrolyzing a solution of KNO3 with copper anode and stainless steel cathode. Right when I turned the power on, the cathode produced lots of gas as normal, and the anode started corroding to a nice blue precipitate, but after about 2 minutes of runtime the SS cathode stopped bubbling completely, and the solution became filled with different hues of green and blue precipitates, also black. I also noticed that the cathode turned a slight copper colour at the top. My electrolyte is about 20 grams of KNO3 in 200ml of water. The cell draws a large current, I measured 2.8A at 5 volts. The solution has a strong smell of ammonia. What's going on? Why did the cathode stop producing hydrogen? Why did copper plate on the cathode? I thought Cu(OH)2 is insoluble. thanks

I use this method to make me CuO. Actually anhydrous cuso4 will start to decompose at about 300C. The 650 figure is the temperature at which it decomps vigorously. The so3 fumes are indeed very choking and irritating. I make it in my room without a fumehood, i just open the window . wouldn't it be possible to condense the so3 (boiling point 45C) and then add water?

The easiest way to make H2SO4 is to just heat up CuSO4 causing it to decompose into CuO and SO3, bubble the SO3 through water and voila. Very efficient and cheap, and way faster than any electrochemical method. And the side product, CuO is very useful as well for the home scientist.