Dissolve Platinum with Chlorine Gas

Dissolve Platinum with Chlorine Gas


Warning: In this experiment we use corrosive hydrochloric acid. Wear gloves when handling it. We also use toxic chlorine gas. Work outside or in a fume hood. Greetings fellow nerds. In previous videos we’ve dissolved platinum with a mixture of hydrochloric acids and nitric acids known as aqua regia. While this works very well nitric acid is somewhat expensive and not that easy to obtain. A much cheaper reagent for dissolving platinum is chlorine gas. To do this is actually pretty simple. Here i have a jar and in the front you can see a vial containing 3 mL of hydrochloric acid and 337 mg of platinum metal powder. This is actually the same platinum powder we made in a previous video on refining platinum. Now in the back of the jar here is 3 vials containing 3 grams each of trichloroisocyanuric acid in 10 mL each of water. Trichloroisocyanuric acid is sold as a swimming pool chemical. These will serve to generate our chlorine gas. It’s a huge excess but that’s because we’re working on a small scale with a relatively large reaction vessel that we need to fill with chlorine. Now i have my 4 vials in a jar here so i can seal it later and keep the chlorine gas in. If you’re using a proper gas bubbling setup with little dead space and a very controlled gas generator, i recommend using an equal mass of trichloroisocyanuric acid to platinum for better reagent efficiency. Okay so let’s get started. I’m opening up the jar and now i’m dropping in 1ml of hydrochloric acid into each of the 3 vials containing the trichloroisocyanuric acid. This forms chlorine gas and i talk about the chemistry of that in a previous video. You can check in the video description to see it. Now let me seal the jar and turn on the stirring. You can see a slight yellowish green haze in the jar as the chlorine is produced and fills it. The lid is loose enough that chlorine can escape if the pressure is too high. Anyway, what’s happening in our solution is that the platinum is reacting with the chlorine and hydrochloric acid to produce hexachloroplatinic acid. Also known as chloroplatinic acid. Okay it’s been twenty minutes now and the water vapor has condensed on the side of the jar. Let me flame heat the jar to boil off the water so we can see it better. Let me turn off the stirring and let the platinum settle. This is the color of hexachloroplatinic acid and proves our reaction is working. Okay let me turn the stirring back on to let it continue. Now this process of using chlorine instead of nitric acid is advantageous for several reasons. As a raw chemical nitric acid is somewhat more expensive than chlorine. So industrial scale refiners can have significant cost savings. Another issue that makes nitric acid even more expensive to use is that nitric acid also decomposes in aqua regia through various side reactions. Since these reactions deplete the nitric acid that otherwise would go into dissolving platinum, you end up needing even more nitric acid than what the ideal chemical equations require. Chlorine and hydrochloric acid have no depleting side reactions. So all the chlorine that’s used in the target reaction is all that is actually needed, further saving costs. This especially important in platinum that takes a long time to dissolved like bulk platinum items or platinum embedded in other materials. If it takes too long then the nitric acid decomposes by itself and you need to keep adding more. But with chlorine you just need to wait longer, you don’t have to add more than the minimum you need. Now another problem when using nitric acid is that excess nitric acid in the resulting hexachloroplatinic acid has to be destroyed. It cannot be recovered and recycled. Excess chlorine gas however can easily be boiled out of the solution and recompressed to be recycled. Not having excess nitric acid to destroy saves considerable time and effort in processing the hexachloroplatinic acid. The chlorine doesn’t even have to be bought. It can also be made by directly electrolyzing the hydrochloric acid in solution using graphite electrodes. I didn’t do that for this experiment however because i want my hexachloroplatinic acid pure and didn’t want bits of graphite floating in it. There is however one very big and obvious drawback of using chlorine over nitric acid. It’s a deadly toxic gas and thus difficult to handle compared to a liquid. It doesn’t dissolve very much in solution so you need to continuously expose it as the reaction progresses. This requires a complicated gas bubbling setup. For very small scales like this 337 mg quantity of platinum we can just use a single sealed jar. But if we scale up we’ll need ever more complicated apparatus. Industrial refiners have no problem dealing with gases but amateur refiners usually shy away from them and for good reason. Now you might be wondering if we can dissolve gold this way. We can and i might try that in the future if there is enough interest. Anyway, here we are a few hours later and all the platinum has dissolved. This was much faster than dissolving our platinum bar because we’re using fine powder with high surface area. Chlorine gas isn’t particularly faster than nitric acid. We now have a relatively pure solution of hexachloroplatinic acid. There is also hydrochloric acid but for my purposes i can use this as is. If you need to remove the hydrochloric acid you can easily boil, evaporate or distill it off. Anyway, that’s how you dissolve platinum with chlorine gas and hydrochloric acid. Thanks for watching. Special thank to all of my supporters on patreon for making these science videos possible with their donations and their direction. If you are not currently a patron, but like to support the continued production of science videos like this one, then check out my patreon page here or in the video description. I really appreciate any and all support.

5 Comments

  1. Can you please show how to obtain and purify potassium hexachloroplatinate from the hexachloroplatinic acid that you made in the other video?

  2. so can I use carbon rods, salt water, and batteries to make the chlorine gas, then add muriatic acid to dissolve my platinum and gold. or do the carbon rods make the chlorine gas without the salt added?

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