Aqua regia and a damned simulator

[rollcast]

One of the tech wizards in my company came up with a chemistry simulator a few years back. It works great and is quite useful, however I ran it this morning to see if I could find the weakest possible solution of aqua regina I could make that would still dissolve gold.

The thing totally **** itself when I added the gold to the aqua regina solution, but when the program unfroze it said there was ice inside the simulation environment?? This thing isn't graphical so you just have to read the print outs and work from there.

The chemistry guy is off on holiday so I have had to search my memory of high school chemistry for answers and can only come to the conclusion is that the amount of bond making occurring in the reaction has absorbed enough heat from the environment to freeze the solution?

Thanks
Richard

Ps. The first simulation said that the lowest temperature was -190^oc, this however could have been a localised anomaly

 

[Borek]

Doesn't sound like something that can happen in this case. If anything, I would expect the solution to get hot.

 

[SpectraCat]

I agree with Borek .. I think you have hit upon a question that the simulator wasn't designed to deal with. I am not sure how it works, but there is no general way to account for all possible cases in a chemical simulator, so it can only give sensible results for systems it is specifically programmed to deal with. Have you used it for gold in aqua regia (note spelling) before and gotten sensible results? If so, then you probably just ran up against a concentration limit or something, where the program went haywire without giving you a sensible error message.

One quibble with your post ... making bonds *releases* energy, so the result predicted by your simulator could only result from energy being absorbed from the solution to break bonds, to the point where the temperature dropped below the freezing point. As Borek said, I would expect the opposite to occur in your example, since the dissolution happens by a redox reaction, followed by a complexation reaction, both of which are exothermic.

 

[rollcast]

Sorry about the mix up on the science of it, I only remember high school hazily.

The simulator was designed to work out concentrations of acids needed to dissolve metals from machined parts and not damage the finished piece, we have had a request to machine some probe tips for someone, the main body is made out of gold and the very tips are electrocoated with platinum, don't know what their for I work in management now and don't deal with the machining.

The aqua regia was needed to clean the pieces before they were plated. We had used it before with aqua regia but never with gold so this is were the problem is.
Thanks
Richard