Sciencemadness Discussion Board

Magnesium acetate?

Steam - 31-3-2014 at 05:32

I have this compound and I am not sure what it is. This is what happened.

I was testing acetic anhydride to see if it would react with Mg, so I place some in a testube and added a piece of clean Mg ribbon. Nothing happend, but I decided to leave it on the testube holder. After almost a month of resting there the experiment looked exactly the same as it did when I started the experiment. Another month passed where I completely forgot about the experiment. Today I was cheningn up my lab and I found the testube again, but this time with these bright white crystals growing from it.
The testube was well sealed with a rubber stopper and was never opened, but what I am guessing is that some moisture got into the testube and caused the Acetic anhydride to change into acetic acid. This reacted with the magneisum to form mg acetate, but because Mg acetate is insoluble in acetic anhydride, it imeaditly crystallized on the ribbon?

Could this be an explanation for the formation of these crystals which could be Mg acetate?

image.jpg - 125kB

deltaH - 31-3-2014 at 06:00

Beware if the magnesium was oxidised, there may be a buildup of hydrogen pressure that may still be ongoing!

Nevertheless, an interesting result. I would certainly keep the product anhydrous if you intend to characterise/investigate the product just in case it is not magnesium acetate (after all you stated that it was well sealed).

I look forward to hearing more about this.

Steam - 31-3-2014 at 06:31

I think I am going to try repeating this experiment but with adding a drop of water to it to see if I get a similar result.

blogfast25 - 31-3-2014 at 09:55

Quote: Originally posted by Steam  
I think I am going to try repeating this experiment but with adding a drop of water to it to see if I get a similar result.


Before anything else you should investigate these crystals. Do they contain magnesium for instance...

[Edited on 31-3-2014 by blogfast25]

AJKOER - 31-3-2014 at 10:32

I would suspect a basic magnesium acetate hydrate. Note, per Wiki on Mg acetate, to quote:

"Reacting metallic magnesium with acetic acid dissolved in dry nitrogen benzene causes magnesium acetate to form along with the release a gas, presumably hydrogen.[9]

Mg +2CH3COOH → Mg(CH3COO)2 + H2 "

implying to me that the normal acetate salt does not form in aqueous solutions with Mg. Probably due to the hydrolysis of the magnesium acetate introducing Mg(OH)2 which could combine with the magnesium acetate to form the insoluble basic Mg acetate salt.

[Edited on 31-3-2014 by AJKOER]

Steam - 31-3-2014 at 10:33

What would be a good way to tell if they had any Mg in them?

Don't have a mass spectrometer at the moment...

nezza - 31-3-2014 at 10:43

The classic test for magnesium is magneson or magnesonII dye. These are azo dyes which are a purplish colour normally. In alkaline solution Mg++ ions bind to the dyes and it goes blue as an attractive precipitate if there is enough Mg++ present or a blue colouration if not. The dyes can be synthesised easily enough if you have the starting materials, para nitroaniline and resorcinol or alpha naphthol.

Steam - 31-3-2014 at 11:31

Quote: Originally posted by AJKOER  
I would suspect a basic magnesium acetate hydrate. Note, per Wiki on Mg acetate, to quote:

"Reacting metallic magnesium with acetic acid dissolved in dry nitrogen benzene causes magnesium acetate to form along with the release a gas, presumably hydrogen.[9]

Mg +2CH3COOH → Mg(CH3COO)2 + H2 "

implying to me that the normal acetate salt does not form in aqueous solutions. Probably due to the hydrolysis of the magnesium acetate introducing Mg(OH)2 which could combine with the magnesium acetate to form the insoluble basic Mg acetate salt.



[Edited on 31-3-2014 by AJKOER]

So you mean Mg acetate but instead of it forming its hydrate with H2O it forms a complex with OH- ions?

DraconicAcid - 31-3-2014 at 12:05

Test the crystals to see if they dissolve in water, or dilute acetic acid. If they do, then test to see if they give a precipitate with sodium hydroxide.

deltaH - 31-3-2014 at 13:08

I'm curious if your test tube released gas when you unstoppered it?

AJKOER - 31-3-2014 at 13:20

Quote: Originally posted by Steam  

So you mean Mg acetate but instead of it forming its hydrate with H2O it forms a complex with OH- ions?

A source for my speculation http://www.google.com/url?sa=t&rct=j&q=basic%20magne... . To quote from page 2 and the bottom of page 4:

"Product insolubles were undesirably high at approximately 5%, due to precipitation of basic acetates (or other basic products) formed during hydrolysis"

and:

....independently confirmed as the stubborn affinity of magnesium acetate for water. In fact, without excess acid present, damp magnesium acetate was shown to hydrolyze significantly during drying."

Some related basic magnesium salts include, for example, dibasic magnesium hychlorite, Mg(ClO)2.2Mg(OH)2, and various forms of the basic carbonate such as artinite (MgCO3·Mg(OH)2·3H2O), hydromagnesite (4MgCO3·Mg(OH)2·4H2O), and dypingite (4MgCO3· Mg(OH)2·5H2O).

[Edited on 31-3-2014 by AJKOER]

Steam - 1-4-2014 at 07:17

Quote: Originally posted by deltaH  
I'm curious if your test tube released gas when you unstoppered it?


Have not unstopered it yet. I am waiting till the weakend when I have time. If there is gas that would indicate acetic acid reacting with Mg. Right?

Steam - 1-4-2014 at 07:24

Quote: Originally posted by AJKOER  
Quote: Originally posted by Steam  

So you mean Mg acetate but instead of it forming its hydrate with H2O it forms a complex with OH- ions?

A source for my speculation http://www.google.com/url?sa=t&rct=j&q=basic%20magne... . To quote from page 2 and the bottom of page 4:

"Product insolubles were undesirably high at approximately 5%, due to precipitation of basic acetates (or other basic products) formed during hydrolysis"

and:

....independently confirmed as the stubborn affinity of magnesium acetate for water. In fact, without excess acid present, damp magnesium acetate was shown to hydrolyze significantly during drying."

Some related basic magnesium salts include, for example, dibasic magnesium hychlorite, Mg(ClO)2.2Mg(OH)2, and various forms of the basic carbonate such as artinite (MgCO3·Mg(OH)2·3H2O), hydromagnesite (4MgCO3·Mg(OH)2·4H2O), and dypingite (4MgCO3· Mg(OH)2·5H2O).

[Edited on 31-3-2014 by AJKOER]


Do you think it would be similar or dibasic magnesium hychlorite (Mg(Ac)2-2Mg(OH)2)

blogfast25 - 1-4-2014 at 08:04

Quote: Originally posted by Steam  
If there is gas that would indicate acetic acid reacting with Mg. Right?


If it is hydrogen gas that would be evidence that an acid has reacted with the magnesium. But right now we don't eve know there is gas and if there is, which one it is.

[Edited on 1-4-2014 by blogfast25]

AJKOER - 5-4-2014 at 12:02

Steam:

Yes, my speculation is a basic magnesium acetate hydrate. However, the precise composition of the double salt could vary depending on reaction conditions. My speculation would be in general Mg(Ac)2.xMg(OH)2.yH2O.

You may be able to determine 'y' by carefully applying mild heat to the salt and noting the change in weight.

To determine 'x' perhaps take two equal volumes of acetic acid. To the first sample of acetic acid, add and record the amount NaHCO3 needed to neutralize. To the second sample, dissolve a known weight of your unknown salt by heating and let stand. Then repeat the neutralization experiment of the first sample. The idea is that any observed reduction in the amount of required NaHCO3 could be due to the presence of Mg(OH)2 in the unknown salt.