Strange, I would have thought water hot enough to burn a frog like that would have killed it in short order. I also am confused how it managed to be burned only on one side. I would think if it was in a container in the sink with water hot enough to burn the hot water would have burned it's whole belly as well and not just one side if by some strange occurrence it wasn't killed outright by the heat. Are you quite sure it was actually burned by the hot water? I have seen similar looking frogs before that were suffering from bacterial infections. Sometimes warm water will make a bacterial infection a lot more obvious. Causes a bacterial bloom I suppose. To be honest though I don't think the frog will live. If it actually is a severe burn I really think it will die from it and if it is actually not a burn but a bacterial infection anti-biotics might save it but the chances are still good it will die.