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Author: Subject: Water plus sodium
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[*] posted on 5-1-2021 at 08:05
Water plus sodium

We've all seen what happens when you drop sodium into water, but I wondered what happens if you drop water onto sodium. Not much with small amounts. Adding water dropwise to an excess of sodium just results in some fizzing and heat leaving a white crust of sodium hydroxide No flames or sparks. I haven't got enough sodium to do this on a large scale, say a thimblefull onto a block of sodium but I suspect the reaction might be vigorous and not safe to carry out at home. Has anyone here tried that safely ?.

If you're not part of the solution, you're part of the precipitate.
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[*] posted on 5-1-2021 at 23:52

Depending on the amount of water, it can be anything from shortly fizzing, then dying down (too little water), heating up and igniting (it burns rather calmly, with some sparking), or with even more water: sputtering like crazy, sending off a cascade of fiery sparks (my personal favourite, even more so than a simple one-time bang). I came to the conclusion that it depends on how much the sodium heats up during the reaction (if it ends up igniting or not) and how much water is still left.

It's difficult for me to give exact ratio of water to sodium for each effect, it was achieved with 0.25-1 g amounts of sodium (all of it done outside for obvious reasons), the amount of water is an empirical "rule of thumb" based on experimentation. But even if you get the right ratio, it's still very unpredictable and may just as well go ka-boom unexpectedly. Generally speaking, the more sodium you use, the bigger the chances of it violently exploding. Surface area is also an important factor at play, a huge lump of sodium and a tiny splash of water probably isn't going to do much. But the same tiny splash might be enough for a 0.5 g cube.

Other stuff I've tried: sodium placed in snow eats through it and sinks to the ground, where it usually dies down again. But a same-sized piece on a block of solid ice can go off like a loud firecracker.
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