[Qaiphyx]

When I dissolve tin in aqua regia, it reacts quite quickly, after the reaction is finished, if the stannous chloride is brought to a boil, say around 320 celsius, the salt will boil for some time, and then for some strange reason suddenly will boil uncontrollably, often escaping the beaker and pouring on to the hot plate, can anyone explain what reaction is occurring here? Also, is there a way to avoid this reaction?

I noticed too that the color will go from a very slight hue of purple, to a slight hue of yellow.

The tin used was 99.9% pure.

[phth]

Thermodynamic runaway: https://en.wikipedia.org/wiki/Thermal_runaway

[zarhym]

Stannous chloride is a common reducing reagent. Especially, SnCl2/HCl system is a common method to reduce nitro group to amine.

I believe that at some point in your reaction, the nitric acid is reduced by SnCl2/HCl. And then, NOx gas is generated in your reaction.

[Qaiphyx]

Thanks!