When Sodium Explodes!

This alkali metal stuff with water is fun!

The weapon of choice is still the HS camera, which shoots 240fps (about 4 milliseconds per frame).  The resolution isn’t great, but it gets the job done.  It can go up to 1000fps, but the resolution drops below 100 pixels.
Both sodium and potassium explode even in modest quantities in water.  Thus far I have been exclusively limited to less that 250 mg (1/4 gram, about the size of a regular aspirin tablet).  Much bigger than this and the hazards amplify horribly.  So the fact finding mission is done on really small quantities.

Sodium tends not to catch fire, then the hydrogen cloud above the metal ignites causing the whole thing to explode with the characteristic pop of a hydrogen explosion.  Not quite sure how that gets the metal to do what it does, or so symmetrically, or why this generates so much light etc compared to the potassium reaction.  The sodium tends to explode within 2-3 seconds, while the potassium takes considerably longer (~8 seconds). Interestingly, if sodium doesn’t explode on the ignition of the hydrogen gas, it tends to just fizz around on the surface.

Sodium explosion in water in slow motion
Sodium explosion in water in slow motion

Sodium is also much more buoyant than potassium and typically floats almost completely clear of the water.  I figure this is a very significant factor in the behavior of the two metals with water.

This is for comparison what the potassium explosion looks like.

Potassium explosion in water in slow motion
Potassium explosion in water in slow motion


10 Responses to “When Sodium Explodes!”

  1. Nate Says:

    Awesome, look forward to the next experiment. Love it when you do these!

    Can you do that experiment where you spread a water molecule over the entire earth someday ?


    Keep up the amazing work Tf

  2. Montybrython Says:

    Amazing, Thank you for reaching out to people(like myself) that would not otherwise understand any of this without your great youtube channel and blog.

  3. Dudley Says:

    Thanks for this!
    Your videos on religion I fully support too (including islam, despite the mass butthurt)

    Doing many pure science videos I really think would help people see the beauty in it a lot easier, as many of your viewers have never properly learnt it and only have ‘your word’ to go on how interesting it is. Beauty in the details, and all that.
    Though you’ve pretty obviously had this conclusion, so; nice move.

    (plus it will prevent some of the vague bullshit comments on your vids)

    Cheers+more math and link to Khan acamedy for those who can’t do basic calc 😛

  4. Tony Klose Says:

    Why do you not have a google ad block for me to click on?…. I generally do this for websites I want to support, since you can’t specifically tell people to click your ads for money.

    • Andy Modell Says:

      Similar to Tony’s comment, is there an RSS feed to your blog updates? All I can locate is one for you youtube videos.

  5. Thunderf00t Says:

    Done (I think). Now an RSS link up.

  6. Ian Says:

    I used to have a job where about once a month, I had to throw a chunk of sodium into a certain pond, in order to keep the pH constant. The best part was, as you might guess, the sodium exploding. Not to mention, the explosion would propel pieces into the air, only to hit the water again and cause several mini-explosions.

  7. Grand Lunar Says:

    I knew sodium reacts violently with water, but never knew other substances did too. Keep up the great work!

    • Ian Says:

      Any alkali metal will react violently with water to form a base; the further down the group you go, the more violently. So, for example, potassium will react more violently than sodium, which in turn will react more violently than lithium 🙂

  8. Satyajay Mandal Says:

    Oh, this is very good

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