Platinum Bar Dissolving in Acid ( Aqua Regia )

Warning: This experiment uses highly corrosive chemicals and produces toxic gases. This should be performed with gloves in a fume hood. Greetings fellow nerds. In this video we’re going to dissolve platinum in a combination of nitric and hydrochloric acids, better known as aqua regia. Here is the platinum bar weighing one troy ounce or 31.1g. Now we add on top 200 mL of concentrated 12M hydrochloric acid. To start we’ll add 25mL of 15M nitric acid, but we’ll add more as we need to. I’m putting on top a round bottom flask of cold water to serve as a crude condensor so we don’t lose as much acid due to evaporation. The solution is heated since the dissolution of platinum is extremely slow at room temperature. What’s happening is the platinum is reacting with nitric acid to produce platinum ions that are then complexed with the chloride ions and dissolve away. The overall reaction produces hexachloroplatinic acid, also known as chloroplatinic acid. This is extremely slow and every four hours i’ve been adding an additional 25mL of nitric acid. Platinum is much more resistance to aqua regia than gold. We’re now at the 11 hour mark and good deal of the platinum is still there. I can’t stay here all night so I’m going to turn off the heating and continue tomorrow. Here we are again the next day. Let me move the bar back into the middle. Overnight barely any platinum reacted at room temperature. Looks like the acid mixture must be heated to get any reasonable dissolution rate for bulk platinum. So I'm going to restart the heating and give it a fresh infusion of 25mL of nitric acid. And there it goes. Now in addition to the platinum dissolving reaction I showed earlier there are also some side reactions that occur when using aqua regia. The nitric acid can react with the hydrochloric acid to produce nitrosyl chloride, chlorine, nitrogen monoxide and nitrogen dioxide. For a quick reaction like dissolving gold these side reactions are not much of an issue. But for a very long reaction like dissolving platinum these side reactions can deplete the necessary nitric and hydrochloric acids before the desired reaction is finished. More acids are needed to complete the desired reaction than what simple stoichiometry would predict. Okay, we’re approaching the 11th hour of our second day, and while the platinum is considerably thinner we’re still not done. I’m going to turn this off and come back tomorrow. Okay here we are on the third day. Let me readjust the camera to get a better look at the platinum. I’m turning the heat back on and adding in another 25mL of nitric acid. I’m also adding in 50mL of hydrochloric acid to replenish what was undoubtedly consumed in side reactions occurring these past two days. There it goes again. I couldn’t add all the nitric acid in at once since it would get consumed in side reactions faster. And we are done. It took about twenty five hours of heating over the course of three days but we have dissolved platinum in aqua regia to form crude chloroplatinic acid. For those that are interested I’ll be processing this into purified chloroplatinic acid in a later video. So please subscribe like and comment. In this video i’ll be processing the crude liquid into purified chloroplatinic acid. In this video we're going to dissolve a gold coin in acid.