Sciencemadness Discussion Board

Why is tin and HCl rxn so slow?

reactofurnace - 27-6-2020 at 16:03

Attempting to purify some tin which I obtained from lead-free solder. The other impurities are most likely silver and copper. My first step was to dissolve some snippets of the tin solder in concentrated hydrochloric acid... however I soon came to the realization that tin's rxn with HCl is excruciatingly slow. Does anyone know why this is? any suggestions on how I could speed it up (apart from heating or refluxing)

j_sum1 - 27-6-2020 at 16:56

I forget which youtuber it was... But I have followed his example:

Melt tin in a large container. Swirl it around while molten so that it solidifies into a thin foil-like shape. Then cut into pieces and dissolve in conc HCl while stirring. This reduces the time from days to a few hours.

I believe it can go faster with heating, but I avoid warming concentrated hydrochloric acid. I think some H2O2 may help too. Worth an experiment.

The issue I believe is the oxide coating. But there may be other factors. Maybe related to crystalline structure, grain size or grain boundaty effects.

DraconicAcid - 27-6-2020 at 17:17

I wonder if copper would catalyze the reaction, as it does for zinc and aluminum.

SplendidAcylation - 27-6-2020 at 17:30

I did this reaction recently

It is indeed very slow, I reasoned that it is because of tin's position in the reactivity series of metals; of the metals more electropositive than hydrogen, tin is the second most electronegative, after lead.

So when it comes to dissolving metals in HCl, lead will be the slowest, followed by tin.

I agree with j_sum1, increasing the surface area and/or heating the acid will both help.

To increase the surface area, I found the following method more effective;
Melt the tin, and drop it from a height onto an appropriate surface.
I dropped a spoonful of molten tin about 2 metres onto tiles, and I got a big splatter of tin, very thin, and without the thick bits that tend to form when doing the swirling method

Then cut it into small pieces.

Even when I did this, it still took days, until I eventually lost patience and boiled it in acid...
This made a huge difference, and what remained dissolved within minutes

Be careful with boiling HCl, if you get it on your skin you'll be okay provided you rinse it off with cold water, but don't get it in your eyes

Also proper ventilation is necessary, as the vapours from hot (and cold, to a lesser extent) HCl will rapidly corrode practically any metal


Quote: Originally posted by DraconicAcid  
I wonder if copper would catalyze the reaction, as it does for zinc and aluminum.


Well I used tin solder which is 99% tin and 1% copper and it still took days; if the copper did indeed catalyze the reaction, I'd hate to see how slow it is without copper! :P

[Edited on 28-6-2020 by SplendidAcylation]

DraconicAcid - 27-6-2020 at 18:02

Quote: Originally posted by SplendidAcylation  
I did this reaction recently

It is indeed very slow, I reasoned that it is because of tin's position in the reactivity series of metals; of the metals more electropositive than hydrogen, tin is the second most electronegative, after lead.

So when it comes to dissolving metals in HCl, lead will be the slowest, followed by tin.


The reactivity series is a thermodynamic listing- kinetics are independent of thermodynamics. There are many single replacement-type reactions which are spontaneous, but just don't go at any appreciable rate. Aluminum won't react with copper(II) ions in the absence of chloride ions; iron will, even though aluminum is much more reactive.

Bedlasky - 28-6-2020 at 02:29

Quote: Originally posted by DraconicAcid  
Aluminum won't react with copper(II) ions in the absence of chloride ions; iron will, even though aluminum is much more reactive.


I once tried reaction between aluminium foil and copper sulfate solution. Aluminium reacts with Cu2+ ions, but reaction took few days. With iron is reaction much faster, even in cold water iron dissolves in few hours.

Sulaiman - 28-6-2020 at 07:36

I would try hammering the tin into flat flakes ot a ribbon.

I once dropped a small ingot of tin into a flask of 36% HCl ... it only took a few weeks to dissolve ;)
A black powder (tin oxide ?) kept loosely coating the surface,
a quick swirl and the powder dissolved very quickly,
so as well as maximising surface area,
some kind of constant agitation should significantly speed up the process - I guess.

Metacelsus - 28-6-2020 at 11:23

From personal experience, Sn/HCl reductions of nitro groups go very quickly, producing tin chloride and an amine hydrochloride. When I did this, I melted the tin and poured it into water to make tin granules, which I then used.

Maybe adding an oxidizer would help speed things up. Or perhaps you could use the tin as an anode in an electrolytic cell.

reactofurnace - 28-6-2020 at 11:37

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by SplendidAcylation  
I did this reaction recently

It is indeed very slow, I reasoned that it is because of tin's position in the reactivity series of metals; of the metals more electropositive than hydrogen, tin is the second most electronegative, after lead.

So when it comes to dissolving metals in HCl, lead will be the slowest, followed by tin.


The reactivity series is a thermodynamic listing- kinetics are independent of thermodynamics. There are many single replacement-type reactions which are spontaneous, but just don't go at any appreciable rate. Aluminum won't react with copper(II) ions in the absence of chloride ions; iron will, even though aluminum is much more reactive.


Interesting point

reactofurnace - 28-6-2020 at 11:39

Quote: Originally posted by j_sum1  
I forget which youtuber it was... But I have followed his example:

Melt tin in a large container. Swirl it around while molten so that it solidifies into a thin foil-like shape. Then cut into pieces and dissolve in conc HCl while stirring. This reduces the time from days to a few hours.

I believe it can go faster with heating, but I avoid warming concentrated hydrochloric acid. I think some H2O2 may help too. Worth an experiment.

The issue I believe is the oxide coating. But there may be other factors. Maybe related to crystalline structure, grain size or grain boundaty effects.


Will definitely try that! Thanks @j_sum1

reactofurnace - 28-6-2020 at 11:42

Quote: Originally posted by SplendidAcylation  
I did this reaction recently

It is indeed very slow, I reasoned that it is because of tin's position in the reactivity series of metals; of the metals more electropositive than hydrogen, tin is the second most electronegative, after lead.

So when it comes to dissolving metals in HCl, lead will be the slowest, followed by tin.

I agree with j_sum1, increasing the surface area and/or heating the acid will both help.

To increase the surface area, I found the following method more effective;
Melt the tin, and drop it from a height onto an appropriate surface.
I dropped a spoonful of molten tin about 2 metres onto tiles, and I got a big splatter of tin, very thin, and without the thick bits that tend to form when doing the swirling method

Then cut it into small pieces.

Even when I did this, it still took days, until I eventually lost patience and boiled it in acid...
This made a huge difference, and what remained dissolved within minutes

Be careful with boiling HCl, if you get it on your skin you'll be okay provided you rinse it off with cold water, but don't get it in your eyes

Also proper ventilation is necessary, as the vapours from hot (and cold, to a lesser extent) HCl will rapidly corrode practically any metal


Quote: Originally posted by DraconicAcid  
I wonder if copper would catalyze the reaction, as it does for zinc and aluminum.


Well I used tin solder which is 99% tin and 1% copper and it still took days; if the copper did indeed catalyze the reaction, I'd hate to see how slow it is without copper! :P

[Edited on 28-6-2020 by SplendidAcylation]



Yess boiling HCl fumes is quite alot to deal with without a fumehood. I may just need to wait for a breezy day.

reactofurnace - 28-6-2020 at 11:44

Quote: Originally posted by Sulaiman  
I would try hammering the tin into flat flakes ot a ribbon.

I once dropped a small ingot of tin into a flask of 36% HCl ... it only took a few weeks to dissolve ;)
A black powder (tin oxide ?) kept loosely coating the surface,
a quick swirl and the powder dissolved very quickly,
so as well as maximising surface area,
some kind of constant agitation should significantly speed up the process - I guess.



Weeks!:o
Okay thanks Ill try to get some way to agitate the mixture.

reactofurnace - 28-6-2020 at 11:47

Quote: Originally posted by Metacelsus  
From personal experience, Sn/HCl reductions of nitro groups go very quickly, producing tin chloride and an amine hydrochloride. When I did this, I melted the tin and poured it into water to make tin granules, which I then used.

Maybe adding an oxidizer would help speed things up. Or perhaps you could use the tin as an anode in an electrolytic cell.


I'll test this out if all else fails. Thanks tho!:D

Tsjerk - 28-6-2020 at 12:06

If you are planning to heat the HCl better dilute it to a little below 20%. That way the HCl fumes a lot less.

Abromination - 28-6-2020 at 22:11

I like to melt the tin and pour it into cool water, forming a rather porous material rather like "mossy" zinc. This gives it a much greater surface area. I also add a small amount of concentrated peroxide to my acid to speed up the reaction and allow the mixture to boil with stirring. As a note, It may help to dilute your acid a bit to prevent an excessive release of hydrogen chloride if your acid is concentrated (I can only buy it as the azeotrope here anyways), although this will slow it down a bit. Still shouldn't take more than a few hours.

AgCollector - 29-6-2020 at 06:59

If you do go with an added oxidizer (such as hydrogen peroxide), it's liable to readily give you Sn(IV) so I'd suggest having an excess of tin metal around, to reduce it back down to Sn(II).

Of course, make sure you are keeping an excess of HCl around too, I'd suggest at least 1 M, to avoid hydrolysis and formation of Sn(OH)Cl.

Out of curiosity, what's the next step after you have SnCl2?


violet sin - 29-6-2020 at 07:49

I found some reading if anyone is interested

THE ANODIC DISSOLUTION OF TIN IN ACIDIC CHLORIDE SOLUTIONS
J. W. JOHNSON and E. C. LIU
Attachment: johnson1974.pdf (478kB)
This file has been downloaded 70 times
8 pages

Corrosion of Tin and its Alloys*
December 2010 DOI: 10.1016/B978-044452787-5.00099-8
author:Stuart Lyon The University of Manchester
Attachment: CS099_Corrosion_of_Tin.pdf (250kB)
This file has been downloaded 86 times
17 pages

SplendidAcylation - 29-6-2020 at 17:06

Quote: Originally posted by DraconicAcid  
Quote: Originally posted by SplendidAcylation  
I did this reaction recently

It is indeed very slow, I reasoned that it is because of tin's position in the reactivity series of metals; of the metals more electropositive than hydrogen, tin is the second most electronegative, after lead.

So when it comes to dissolving metals in HCl, lead will be the slowest, followed by tin.


The reactivity series is a thermodynamic listing- kinetics are independent of thermodynamics. There are many single replacement-type reactions which are spontaneous, but just don't go at any appreciable rate. Aluminum won't react with copper(II) ions in the absence of chloride ions; iron will, even though aluminum is much more reactive.


That's interesting, I stand corrected :)

I have tried the aluminium + copper (II) reaction, and I was indeed surprised to find it didn't work, I just assumed it was due to the passivation layer

almaz - 26-10-2020 at 20:06

Hi, everybody. Tin is known to be reluctant to dissolve in HCl. Pt can speed up its dissolution. This is a galvanic pair. It should be in the form of a wire or a whole metal. It will not be used up, and You can return it back.

Fyndium - 26-10-2020 at 22:29

When I reacted lead, I smelted it and poured it into water through a sieve. It formed fine shots, which increased the surface area significantly compared to a simple block of lead.

almaz - 26-10-2020 at 23:27

Even if the tin is in the form of a foil, it will take a very long time to dissolve. I made a dissolution of two identical pieces of tin by weight. 1 Without platinum and 1 with platinum. At the same time, without Pt, it does not dissolve even after 2 days. If you want to speed up the dissolution even more, then heating is necessary.

teodor - 27-10-2020 at 06:56

Do you think the usage of Pt is more affordable way than just aqua regia ?

symboom - 27-10-2020 at 08:48

There has got to be a way to speed it up with peroxide

almaz - 27-10-2020 at 09:49

I do not know if this is available for beginners. They asked How to speed up the dissolution. I gave the answer.

teodor - 27-10-2020 at 10:26

I think addition of nitrate e.g. KNO3 should speed up the reaction, because it will form a kind of aqua-regia in-situ. Just need to try.

[Edited on 27-10-2020 by teodor]

teodor - 31-10-2020 at 09:44

OK, I've tried that, eventually.

I must admit that the usage of aqua regia vs 36% HCl has no speed benefit.

I did the experiment by dissolving pieces of tin metal I created by dropping the melted metal through a small glass funnel into glicerol and water (they are quite similar, have a shiny surface; the usage of glycerol is more convenient because it doesn't create kind of steam explosions but do it under ventilation).

I used both big and small pieces.

The aqua regia was prepared by mixing 6 ml of 36% HCl and 2 ml of azeotropic HNO3 (the fraction distilled on 121C).

Both tubes show good reaction but aqua regia seams produce 2-3 times more bubbles, so the speed is higher. But I noticed it is just because this reaction is exotermic (it oxidise tin to valence IV) and when I heated the second (pure HCl) tube to the same temperature on a water bath the speed of bubbles was almos the same:

Sn_aqua_regia.jpg - 76kB

Also I tried to dissolve KNO3 in 36 HCl, but it didn't. So, I've prepared solution of KNO3 in boiling water and have poured it into 36% HCl. It immediately produced precipitation of KCl and created some mixture with the same color as the genuine aqua regia, but this need to be decanted from KCl crystalls because they prevent to use it for dissolving of metals.

Generally, with or without usage of water bath, 36% HCl attacks tin pretty well, I can compare with its action on chrome metal, well a bit slower but still doable.

If you have different experience that is probably due to usage of some alloy, not a pure ("crying") tin.



[Edited on 31-10-2020 by teodor]

MidLifeChemist - 31-10-2020 at 15:41

Quote: Originally posted by SplendidAcylation  


I have tried the aluminium + copper (II) reaction, and I was indeed surprised to find it didn't work, I just assumed it was due to the passivation layer


If you add a pinch of table salt, aluminum + copper (II) happens quickly, within 30 minutes. I've produced a good amount of copper that way. Without the pinch of NaCl, nothing happens.