Decontamination of metals

[paulsutton]

In an attempt to get back in to doing some more home chemistry and also come up with ideas for a STEM group i am running,. I recently had a go at seeing what would happen if various metallic elements were added to White Vinegar.

So using 3 test tubes, Magnesium Ribbon, Copper foil and Zinc Granuals (all i have access to at the moment),  I added these to the vinegar

So given that the latter two don't react,  I can probably re-use,  but rather than simply putting back in the containers they came from, is there a easy way to clean them (not sure if that is the right term).

I was thinking of just adding to a beaker of water to hopefully remove any residue of White Vinegar (Acetic Acid) so basically giving them a quick wash and dry them off.

It may not be needed, however it is probably good practice to do so.

Also, as the magnesium reacts,  As it has been it a container for a long time before I used it, and most of the shine has gone so it is tarnished,  what is the best way to clean it please.  I have tried a rubber thing I use to clean vero / strip board before soldering, and also a wire brush,   anything else i can try.   Would be nice to have a better surface area for future attempts.

What did surprise me what that within an hour the magnesium had reacted which is kinda cool really,  ( I didn't use much to begin with)  not quite sure what to do with what was produced,  which i think is probably Magnesium Acetate,  must be able to use for some other experiment somewhere.

Thanks for any help / advice.

 

Paul Sutton

[exchemist]

2 hours ago, paulsutton said:

In an attempt to get back in to doing some more home chemistry and also come up with ideas for a STEM group i am running,. I recently had a go at seeing what would happen if various metallic elements were added to White Vinegar.

So using 3 test tubes, Magnesium Ribbon, Copper foil and Zinc Granuals (all i have access to at the moment),  I added these to the vinegar

So given that the latter two don't react,  I can probably re-use,  but rather than simply putting back in the containers they came from, is there a easy way to clean them (not sure if that is the right term).

I was thinking of just adding to a beaker of water to hopefully remove any residue of White Vinegar (Acetic Acid) so basically giving them a quick wash and dry them off.

It may not be needed, however it is probably good practice to do so.

Also, as the magnesium reacts,  As it has been it a container for a long time before I used it, and most of the shine has gone so it is tarnished,  what is the best way to clean it please.  I have tried a rubber thing I use to clean vero / strip board before soldering, and also a wire brush,   anything else i can try.   Would be nice to have a better surface area for future attempts.

What did surprise me what that within an hour the magnesium had reacted which is kinda cool really,  ( I didn't use much to begin with)  not quite sure what to do with what was produced,  which i think is probably Magnesium Acetate,  must be able to use for some other experiment somewhere.

Thanks for any help / advice.

 

Paul Sutton

You might want to brush up on the Electrochemical Series. That tells you which metals are expected to react with acids to liberate hydrogen (basically anything with an electrode potential that is -ve relative to hydrogen, which is set at zero by convention.) An example here: https://chemguide.co.uk/physical/redoxeqia/ecs.html

According to this, Mg is expected to react, and Cu is not. Zn however is slightly -ve, so would be expected to react, but not as vigorously as Mg. But there may be a protective oxide layer that interferes -  I can't remember.

The reaction product with Mg should indeed be MgAc.

If the Mg strip has an oxide layer, I should think rubbing with wire wool (i.e. a scouring pad without soap impregnation) would be one way to get that off. 

Other, less ancient, chemists may be able to add to this or correct it...... 

Edited January 4, 2023 by exchemist

[paulsutton]

16 hours ago, exchemist said:

You might want to brush up on the Electrochemical Series. That tells you which metals are expected to react with acids to liberate hydrogen (basically anything with an electrode potential that is -ve relative to hydrogen, which is set at zero by convention.) An example here: https://chemguide.co.uk/physical/redoxeqia/ecs.html

According to this, Mg is expected to react, and Cu is not. Zn however is slightly -ve, so would be expected to react, but not as vigorously as Mg. But there may be a protective oxide layer that interferes -  I can't remember.

The reaction product with Mg should indeed be MgAc.

If the Mg strip has an oxide layer, I should think rubbing with wire wool (i.e. a scouring pad without soap impregnation) would be one way to get that off. 

Other, less ancient, chemists may be able to add to this or correct it...... 

Thanks for this,   much appreciated  it is a fun experiment to do.    I have just given the Magnesium a rub with a sanding block,  works a treat,   nice and shiny as it should be.    Will look up the electro chemical series too.

 

Regards

 

Paul

[exchemist]

29 minutes ago, paulsutton said:

Thanks for this,   much appreciated  it is a fun experiment to do.    I have just given the Magnesium a rub with a sanding block,  works a treat,   nice and shiny as it should be.    Will look up the electro chemical series too.

 

Regards

 

Paul

OK have fun. Try it with zinc too -  I'm a bit surprised you saw no reaction. 

By the way, I should have said Mg(Ac)₂ of course. 

[paulsutton]

Thanks for this, I will have another go with the Zinc,  could be that it is again older, and also tarnished / oxidised.   I have attached a picture of the magnesium,  as a comparison before and after cleaning a piece.  The zinc reaction may just be a lot slower, or hindered by the contamination.

With Mg(Ac)₂,  I take it the (Ac))₂  is for acetate,  so a shorthand form of Mg(CH₃COO)₂

Just asking as If I need to explain this to others,  it makes it easier. 

Nice to know about these shorter forms of writing formulaie

The zinc I have here is very grey,  as they are graduals a little more challenging to scrub wit something abrasive, compared with the Magnesium.

 

[exchemist]

1 hour ago, paulsutton said:

Thanks for this, I will have another go with the Zinc,  could be that it is again older, and also tarnished / oxidised.   I have attached a picture of the magnesium,  as a comparison before and after cleaning a piece.  The zinc reaction may just be a lot slower, or hindered by the contamination.

With Mg(Ac)₂,  I take it the (Ac))₂  is for acetate,  so a shorthand form of Mg(CH₃COO)₂

Just asking as If I need to explain this to others,  it makes it easier. 

Nice to know about these shorter forms of writing formulaie

The zinc I have here is very grey,  as they are graduals a little more challenging to scrub wit something abrasive, compared with the Magnesium.

 

I used the term Ac a bit wrongly actually. Ac, strictly denotes the acetyl group, which is CH3CO - so I should have said Mg(OAc)₂. I'm retired and very out of practice, I'm afraid. Probably best to refer to it as Mg (CH3COO)₂ , to avoid getting into a nomenclature minefield.

Regarding Zn's apparent low reactivity, acetic acid is a weak acid. At molar concentration (similar to vinegar), only about 0.4% is dissociated into H+ and acetate. If you had a molar strong acid, e.g. HCl, the reaction would be more obvious I think.  

 

[paulsutton]

8 minutes ago, exchemist said:

I used the term Ac a bit wrongly actually. Ac, strictly denotes the acetyl group, which is CH3CO - so I should have said Mg(OAc)₂. I'm retired and very out of practice, I'm afraid. Probably best to refer to it as Mg (CH3COO)₂ , to avoid getting into a nomenclature minefield.

Regarding Zn's apparent low reactivity, acetic acid is a weak acid. At molar concentration (similar to vinegar), only about 0.4% is dissociated into H+ and acetate. If you had a molar strong acid, e.g. HCl, the reaction would be more obvious I think.  

 

I can try with Citric Acid,   not sure if I have anything else,  Sodium Hydrogen Sulfate is acidic, but i don't think Magnesium will displace the Sodium.

This is the fun of home chemistry,   experiments and researching this.

[exchemist]

2 hours ago, paulsutton said:

I can try with Citric Acid,   not sure if I have anything else,  Sodium Hydrogen Sulfate is acidic, but i don't think Magnesium will displace the Sodium.

This is the fun of home chemistry,   experiments and researching this.

I think you can get drain cleaner which is based on strong acids (some is also based on strong alkali), but I hesitate to suggest you try, as they are fairly nasty if you spill them on you - or anything else. Citric acid has a first pKa of 3.1  whereas acetic acid has a pKa of 4.76, so citric acid is a bit stronger but not much. (For comparison a strong acid such as HCl has a pKa of -6, so in a different ballpark entirely).