[lotharien]

hi , i'm new , sorry for my bad english.

this is my question :

i have dissolved metallic aluminium in a very basic solution of ethyl alcohol and NaOH.

the product of the reaction is a black sticky viscous gel , insoluble in ethyl alcohol , soluble in water.

if diluted in water we have obviously the transfotmation in Al(OH)3.


what we can suppose about the black compund ?

is a dehydrated form of Al(OH)4- ? like AlO2 + 2(CH3CH2OH)

mabye is a polymer ? like -(-AlO-O-AlO-O-AlO-)- (i say this because of the strange sticky behavior of the compund)


any ideas

[BluRay]

I presume it's Al(OH)₄^-.

[lotharien]

I presume it's Al(OH)₄^-.

how do you explain the black colour , and the sticky behaviour ?

[BluRay]

how do you explain the black colour , and the sticky behaviour ?

I don't explain it, if the chemicals were pure. Are you totally sure of it? Maybe the Al had some little percent of other metals in the alloy?

[lotharien]

how do you explain the black colour , and the sticky behaviour ?

I don't explain it, if the chemicals were pure. Are you totally sure of it? Maybe the Al had some little percent of other metals in the alloy?

it is possible but the percent are very very low. what metal can be responsible of the behaviour in your hypothesis?

[BluRay]

it is possible but the percent are very very low. what metal can be responsible of the behaviour in your hypothesis?

Maybe copper, its oxide is black (the hydroxide decomposes easily to oxide with heat).

[lotharien]

it is possible but the percent are very very low. what metal can be responsible of the behaviour in your hypothesis?

Maybe copper, its oxide is black (the hydroxide decomposes easily to oxide with heat).

no it is inpossible because , at ph 10 the solution turn to white (Al(OH)3) , if i have copper it will be blue

[BluRay]

no it is inpossible because , at ph 10 the solution turn to white (Al(OH)3) , if i have copper it will be blue

Why should it be blue?

[lotharien]

copper idroxide

[BluRay]

copper idroxide

But just 4 posts ago I was discussing the possibility that copper hydroxide decomposes by heat:

<<Maybe copper, its oxide is black (the hydroxide decomposes easily to oxide with heat).>>

[lotharien]

copper idroxide

But just 4 posts ago I was discussing the possibility that copper hydroxide decomposes by heat:

<<Maybe copper, its oxide is black (the hydroxide decomposes easily to oxide with heat).>>

i'm talking about of a really basic solution , in this conditions all the copper will turn to oxide. but if i take this solution and i decrease the pH with HCl the copper oxide will return in solution as an hydroxide , if i use a lot of HCl then it will turno to ion form .

[BluRay]

copper idroxide

But just 4 posts ago I was discussing the possibility that copper hydroxide decomposes by heat:

<<Maybe copper, its oxide is black (the hydroxide decomposes easily to oxide with heat).>>

i'm talking about of a really basic solution , in this conditions all the copper will turn to oxide. but if i take this solution and i decrease the pH with HCl the copper oxide will return in solution as an hydroxide , if i use a lot of HCl then it will turno to ion form .

That's for sure. If that black stuff doesn't become at least green-yellow with HCl, you can exclude copper. You didn't mention this in your previous posts.
What about solid aluminum hydroxide and/or solid aluminum metal dispersed in very fine powder?

[lotharien]

-we can exclude solid aluminum metal dispersed because if i diluite the solution all is transformed in Al(OH)3 and nothing else remain.
-solid aluminium hydroxide , or one of his dehydratated form , are all white

if i heat the black compund with an open flame , it immediately turns in a white sponged compund (probably sodium alluminate).

[BluRay]

-we can exclude solid aluminum metal dispersed because if i diluite the solution all is transformed in Al(OH)3  and nothing else remain.
-solid aluminium hydroxide , or one of his dehydratated form , are all white

Yes, in the pure form, but all times I have dissolved pieces of commercial Al with acids or bases, it never formed pure white solutions/dispersions, always grey.

[lotharien]

i think the grey colour depends on this :

dissolution with acids: incomplete dissolution , metal powred remain in sunspension.

dissolution with bases: brown/grey sunspension of some aluminate products , (like silicate it combines in macromolecular forms ), they are insoluble , and do not react easily with acids.

we have some aluminate product in our ehtyl alcohol, like all dissolution af Al in bases , but in this conditions it is black and sticky