# Why does adding salt to boiling water cause it to flare up suddenly?

I was expecting that the water would become less "boily" since the ions in $\ce{NaCl}$ would require energy to disassociate. Instead it turned whitish and the water level suddenly rose and then subsided. I think the white color can be attributed to the fact that table salt is white but why did the water suddenly flare up ?

• – Mithoron May 5 '18 at 16:18

It seems that water does not begin boiling at 100.001 degrees C. A pot of water keeps getting hotter and hotter until it produces $$H_2O$$ vapor at a rate sufficient to produce a visible bubble in one location, and then turbulence shakes some more vapor free. The extra nucleation sites proposed by Waylander suggests that most pots don't have many nucleation sites. Of course! Who wants a rough pot that is hard to clean? Much preferred is a smooth pot. Other nucleation sites (or turbulence) can cause the same boil-up: pasta added to a slightly boiling pot will flare up too. And this suggests that the hot water is actually hotter than equilibrium, either because of a hotter temperature than 100 degrees, and perhaps the vapor bubbles in the water are actually at a little more than atmospheric pressure, or that the vapor space just above the hot water is not 100% water vapor (i.e., not 1 atmosphere of $$H_2O$$), so more water vapor produced by more nucleation sites can be instantly accommodated if a boil-up occurs - this is not an adjustment of an equilibrium, but a collapse of a non-equilibrium situation.