How to Purify by Recrystallization

We show how to purify aluminum nitrate and strontium nitrate by recrystallization. This is important because those two substances must be extremely pure for our upcoming video on making glow in the dark powder.


Dissolve the dry aluminum nitrate in water and filter off any insoluble materials. We could not filter it off before it dried in the previous video because the particles at that stage are much too small. It needs crystallize once to aggregate into particles large that can be filtered.


After drying, carefully weigh out the crystals. Then take that mass and add in 20% mass of water. So if you have 50g like me, you add 10g of water (or 10mL since density is 1g/mL).

It won't all dissolve, so carefully heat the mixture until it dissolves. Then cover it and let it cool down. Eventually it'll crystallize out purer crystals.

After the mixture cools to room temperature, and left for a few hours. The liquid is poured off and discarded, it has the impurities and is not needed.

The crystals are again weighed and once again they are recrystallized with 20% water.

Once this is done. Dry the final product. I started with 50g and ended up with 17g. But now it's very pure. Better than 99%

Strontium nitrate also needs to be purified. But it's solubility doesn't change that much with temperature so we'll have to purify by slow evaporation recrystallization rather than thermal cycle recrystallization.


Once again, dissolve it in water and filter it. Then let it crystallize. But before it dries completely, let the liquid reduce to about 20% of it's saturated volume. So I started with a saturated solution of 10mL of strontium nitrate, i then waited until it evaporated down to 2mL of fluid. The crystals are not included in this assessment. Then discard the liquid. Repeat the recrystallization process.

Once again, use the desiccator bag to obtain extremely dry chemicals.

We are now ready to produce glow-in-the-dark powder.

[NurdRage]

Why in Einstein's name does this have millions of views? It sucks. Seriously, i'm the guy who made it... and even i'll tell you; it SUCKS.
Anything! But not this video.

[JMA]

What we have are solubility tables, which tell us the solubility of our compound at different temperatures in different solvents. We look for a solvent where the compound has low solubility at room temperature (or colder) and high solubility at hotter temperatures. This is ideal, as the crystals will come out when the solvent cools from being heated, purifying them. This is the general idea of recrystallization.

[CannaPlant]

This is the first explanation of the process of recrystallization that makes 100% sense and answers all my questions. Thank you!

[NurdRage]

@myrdale

I tried that but the purity just wasn't good enough to make phosphorescent powder.

[milotickz]

Of all the scientists on youtube, you NurdRage, are the BEST!!!

[gregorteply]

I love him saying "product" all the time.

[NurdRage]

@fedaikn

the crystals are pure enough for the synthesis of phosphorescent powder.

And you do get rid of most of the liquid, and thus of the impurities, when you decant off the liquid.

[NurdRage]

@personperson666

While it does improve the crystal growth somewhat, eventually you reach a limit where the size is dictated by other variables like size of the container, temperature, humidity, etc.etc.etc.

[NurdRage]

@ryan50ryan

simply let it dry. But it will be chock full of impurities, and useless for making glow powder. If you have other uses that can tolerate the impurities then go for it, otherwise its best just to discard it.

[irxkep]

You can actually save the impure liquid that has been poured off and let it dry. This way you will have some pure and some impure product that can still be used in reactions that can tollerate impuritys

[NurdRage]

@Pipewing

Generally, the slower the recrystallization is done, the purer it is.

Sometimes you can come across the solubility tables in the literature, other times you just have to try it yourself. :)

[baguazhang]

Thanks for the help. I'm purifying azides in different solvents and it's working well so far. I just added a bit too much solvent and need to evaporate some off.

[drahyden]

Recristalization, great technique. Thanks for positing this vids, you are really making a excellent service of inciting the love for chemistry on people.

[AnyerPablo]

i want to ask if i want to make 100kg kclo3 what steps should i do?

[sulkarnaink]

may I ask for a complete video with the ingredients needed and how to make it

[NurdRage]

MnO2 isn't soluble in water so it requires a chemical purification process.

if i make ask, what do people use MnO2 for other than an h2o2 catalyst? if the use is interesting i might do a video on it.

[NurdRage]

@tzermaan
I'm actually trying to put together such a DVD myself. Once i have a few more videos, as well fix some mistakes and edit a few issues, i'll release such a DVD directly.

[JamesAJ]

Am I the only one who's fascinated by this science here? Everyone else is disliking "cause Breaking Bad"...

[NurdRage]

@mafl25

yeah, but it's now chock full of impurities. After all, to make one portion purer the impurities have to go somewhere.

Just save the discarded liquids and dry them. If you can find a use for them that isn't sensitive to impurities then go for it.

[starshock]

After heating, placing the heated solution in the beaker into a styrofoam or insulating container will yield larger crystals but will take longer to cool.