Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Zerhacker on June 03, 2015, 12:52:21 PM
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I work in a biology lab, and I was required to make 1 litre 10M concentration of NaOH from NaOH pellets. Long story short, I made the mistake of adding 800ml of water directly to 400 g of pellet. Upon realising the amount of heat generated from the reaction, I quickly removed the water from the glass bottle. Now the pellets have hardened at the bottom of the bottle. Our department does not accept disposal of chemical in inappropriate container, as NaOH does slowly eat through glass. Does anyone have a safe and efficient way to remove the crystallized NaOH from the bottom of the bottle and to safely dispose of them?
Thank you in advance!
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Can't you dissolve the solid in water, and dispose of the liquid the same way you dispose of any other liquid waste?
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If i add water directly to the bottle it might heat up too quickly and explode, as i have ~400g NaOh in a small 1 L bottle. During the initial mix the bottle got so hot that it is difficult to hold. The crystal is also fairly hard and impossible to chip off using a measuring spoon, not to mention that it might produce airborn powder in the process
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Then don't add a lot of water at once, but just a few mL now and then.This way you should be able to build enough volume inside to dissolve everything in a day or two. Even if it takes few days it should be perfectly safe.
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Presumably, this bottle is Kimax or Pyrex, and can handle minor heating of the sort Borek: mentions, or even more if you're not as careful. I'm still left confused ... you originally posted this in Chemical Engineering, are you looking for a hi-tech way to get the solid out? If I suggest that you scrape it out with a spatula, are you still worried about a very energetic reaction? Its important to be aware of safety, but you're going a bit overboard. I expect you to ask if you can use any spatula ... and you certainly can: metal, porcelain, glass stirring rod, spare wooden tongue depressor.
Here's funny story, I massed out a bunch of NaOH pellets, and I wanted to add some distilled H2O (I was making some strong NaOH solution to pH adjust a buffer, so amounts aren't important.) Anyway, I had the pellets in a weigh dish in my hand, and I went to the dH2O tap, and I'd forgotten the heat exchangers were offline. So 70 C H2O hits NaOH and immediately begins to boil -- the water boiled away in seconds, leaving a dry powder of NaOH, and me going "Uh..Uh..Huh" My hand didn't even get hot, it actually felt cool. I was fine, behind my safety glasses, lab coat, and nitrile gloves ... but I wouldn't try it in my hand twice.
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From practical side. Take a 20 liter bucket and fill it with water . Go somewhere out side and immerse the bottle into it. I think the NaOH already got water before and also Carbon dioxide. I don't think a heavy reaction will take place.
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The secondary container approach suggested by Hunter2 is also how I would do this.
You can probably dispose of dilute (<1 M) NaOH down the sink if it is otherwise uncontaminated (NaOH is the active ingredient in most drain cleaners).
Also, I would recommend a plastic bottle for 10 M NaOH next time - it wouldn't have avoided the situation you are in now, but strong caustic solutions react slowly with glass.
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Thanks all! We have disposed of the NaOH by slowly dissolving the mass in a few ml of cold water at a time.
@Arkcon, thx for moving my post to the correct subforum. I only posted in the chemical engineer forum because ive read a post about disposal of large quantity of concentrated NaOH in the subforum, and thought that itll be a good place to start.