Make Aluminium Hydroxide (fail)

My attempt at making aluminium hydroxide using a reaction described on Wikipedia under the listing for aluminium sulfate.
The reaction appears to work except isolation of the product seems to fail.

[@chemicalmaster3267]

+Perry Gershin Next time use ammonia solution instead of sodium bicarbonate. That´s how I made mine and it´s a really clean and better method.

[@perrygershin3946]

That sounds like something I might try. Would this be the correct equation for the reaction you describe? Al2(SO4)3 + 6 NH4OH = 2 Al(OH)3 + 3 (NH4)2SO4 I wonder why I had so much bicarbonate remaining after my method? Was the stoichiometry wrong or did the reaction not go to completion? Anyway, thanks for the tip.

[@chemicalmaster3267]

​@@perrygershin3946 Maybe there was excess sodium bicarbonate. And you heated the water when you were dissolving the sodium bicarbonate if I remember correctly, right? I even saw for myself that sodium bicarbonate also decomposes into sodium carbonate, carbon dioxide and water when heated in aqueous solution not just when heated dry. I don´t know, this just an hypothesized idea, but maybe the aluminium hydroxide is somewhat porous and a bit of somewhat could have been trapped inside it. Maybe that could be explain the slight fizzing when you tested a sample with some hydrochloric acid. And the correct equation for the reaction between aluminium sulfate and aqueous ammonia is: Al2(SO4)3 + 6 NH3 + 6 H2O = 2 Al(OH)3 + 3 (NH4)2SO4. From what I´ve heard ammonium hydroxide doesn´t exist and aqueous ammonia is the correct term for a solution for ammonia in water.

[@perrygershin3946]

It was actually a few months ago when I did this experiment. I had held back from uploading it because it was a fail. I finally decided to upload it to see if anyone had any ideas what went wrong. My memory may be a little fuzzy on some of the details because so much time has passed. I do know that sodium bicarbonate will decompose when heated above a certain temperature and (I think) I only used modest heating to help get it all into solution but I'm not sure now. I really can't understand why there would have been much excess bicarbonate remaining if the reaction went to completion. Maybe there is something to your 'trapped inside' hypothesis, maybe it slowed or stopped the reaction from going to completion. If I do it again I will definitely let it go much longer. The way I remember it is that ammonium hydroxide effectively exists only in solution and not as an independent compound but you are technically correct. Anyway for stoichiometry one would need to know the concentration of ammonia in the water and your equation would work fine.

[@jtbmetaldesigns]

I’ve used 20-25% sodium hydroxide solution to remove smeared aluminum from dremel burrs and it works great. I also use a 3-4% sodium hydroxide solution to strip anodizing off aluminum quite effectively. In the diluted alkali, I noticed a white deposit on the bottom. Perhaps this was the stripped anodize settling as aluminum hydroxide. FYI, most dyes remain in the alkaline solution. What I propose is to dissolve aluminum in 20-25% sodium hydroxide. Extreme caution is advised as this could in fact be an energetic reaction with alkaline solution possibly overflowing containers if precautions not followed. When a clear concentrate is obtained, dilute with 8 to 10 times by volume with water. Aluminum hydroxide should crash out since sodium aluminate is unstable in dilute solutions.

[@abdurraheem4819]

Hi i want to make aluminum hydroxide from bauxite ore and react with sodium hydroxide kindly guide me how can i Precipetate aluminum hydroxide from it

[@shinigami-man5727]

First! Really enjoyed your potash videos. Really helped clear up some things for me. Thank you!

[@perrygershin3946]

Thanks for the comment shini, glad you enjoyed.

[@mspalien]

I suspect what you have made is basic aluminum carbonate Al(OH)CO3

[@dragoscoco2173]

Adding sodium was not a great way to react the aluminium as you can easily complex it and get a mixture of sodium aluminate with various sodium aluminate carbonates unless the two were in a somewhat exact perfect mixture. I suppose your Alum was hydrated meaning you used way too little compared to pure anhydrous. Try to heat the alum to see if it looses water.

[@perrygershin3946]

Thanks for the comment. It's been so long that I really can't remember if I heated it first or not. Probably not.

[@johnblacksuperchemist2556]

PERRY.................When i wash an insoluble hydroxide...because they clog up a filter so easily and trap in water so easily...if i made a small amount like you did i would put it in like a half gallon or gallon vessel (like the size you would make lemon aid or kool aid in) and fill with water and stir it good then put plastic wrap over the top and let it sit until all or most of the hydroxide settle to the ground. Then pour most of the water off without pouring out the hydroxide and then fill the container back up with water and stir and cover with plastic and keep repeating until you do it 6 or 7 times and then after you pour off most of the water the last time just put it in a filter and wash with a little water and suck the cake dry with vacuum and then IF IT STILL HAS CARBONATE IN IT then the reason why is that you are also making something called "basic aluminum carbonate" Al(HCO3)(CO3). And if that is the case which i think it is. Then you should try using a hydroxide instead of a carbonate. Maybe like sodium hydroxide or ammonium hydroxide.

[@1brytol]

I prefer making first an ammonia complex of the metal, and only than adding sodium hydroxide. At least in case of copper(II) hydroxide, it made a lot purer product than just dumping in base. I'm not sure what would it look like with Al(OH)3, but I think it would look simmilar.

[@1brytol]

I think I have an idea how could you purify it. React it with a weak acid that will react only with the carbonate (presumably it is leftover sodium carbonate left in soaked up water that precipitated out when drying). For example do some acetic acid washings until no more visible bubbling occurs, wash it with distilled water and it should be quite pure.

[@esinti8735]

What are the necessary materials and method for aluminum sulfate?

[@fahadalshammry9667]

I prepared aluminum sulfate by adding sulfuric acid to aluminum foil in a beaker and heating it

[@IlusysSystems]

Dunno exactly what went wrong here, but I am thinking why not from sodium aluminate then react with hydrochloric acid to get sodium chloride and aluminium hydroxide?

[@perrygershin3946]

Thanks for the reply. My experience is no matter how you make it, it is really difficult to filter out of solution. If you really need it, Amazon sells it cheap. But that defeats the purpose of the 'do it your self' hobby part.

[@IlusysSystems]

@@perrygershin3946 hm interesting, I run reaction as I proposed today, and it worked really well. As for filtering - I find that it is easier to just wash clay-like substances multiple times with clean water. Sure, it's a pain, as to remove __all__ soluble salts you typically have to use about 10l of water per ~100g of product each time cleaning product with about 2l of water, wait for solids to settle and syphon witn minimum losses possible. Sure we can get stuff on amazon, but sometimes you just need it right now...