Crystal growing

[paulsutton]

I tried to grow some Salt crystals a while back, it worked using table salt, however this also contains Sodium Ferrocyanide.   Would I be better using pure Sodium Chloride (from a chemical supplier) ?

I think the crystals should be more cuboid shaped,  which I think is how the molecular structure is for Sodium Chloride.  I have attached a photo of my previous attempt results. 

I am not what the Sodium Ferrocyanide does,  it is an anti caking agent or something. so that may explain the results.

 

Thanks

 

Paul

Edited November 23, 2021 by paulsutton

[exchemist]

41 minutes ago, paulsutton said:

I tried to grow some Salt crystals a while back, it worked using table salt, however this also contains Sodium Ferrocyanide.   Would I be better using pure Sodium Chloride (from a chemical supplier) ?

I think the crystals should be more cuboid shaped,  which I think is how the molecular structure is for Sodium Chloride.  I have attached a photo of my previous attempt results. 

I am not what the Sodium Ferrocyanide does,  it is an anti caking agent or something. so that may explain the results.

 

Thanks

 

Paul

I'm not sure that the sodium ferricyanide will interfere to that extent. @John Cuthbermay know better.  But as I recall, to grow a nice cuboid crystal you need to suspend a "seed" crystal, tied with a cotton thread or something, in a supersaturated solution and let it grow slowly and undisturbed for several days. What you want is for just one crystal to grow slowly, rather than a mass, suddenly. Maybe if you have some coarse salt you can select one grain and use that. Important that there are no other crystals or particles in the supersaturated solution or these will also be nuclei for crystallisation.

[John Cuthber]

I think that part of the reason they use ferrocyanide is that it alters the crystal growth leading to a change in caking behaviour and also perhaps crystal form.
 

Adding a little copper sulphate solution to the salt solution will form an insoluble copper ferrocyanide precipitate which you can filter off.
People are still doing work on this sort of thing
https://pubs.acs.org/doi/full/10.1021/cg201661y?mobileUi=0

It's a good idea to filter solutions before letting them crystallise, even if the best you can do it so filter through a paper tissue.

However, I think the problem you have there is capillary creep. A couple of drops of cooking oil on the string above the level of the liquid may help keep the solution where it is meant to be.

[StringJunky]

Would DI/distilled water help as well?

[MigL]

Single crystals grow best along a gradient.
Temperature, pressure, what have you.

[paulsutton]

Thanks for this,  I have copper sulphate in with my chemistry kit,  so can give that a go.

I think i need to find a way to grow the initial seed crystal then.

I am about to start as a TA in a primary school.  There are various ideas here,  perhaps we can investigate as a class too.   It would need the usual risk assessment  though which is fine, as i can find the materials safety data sheets for everything.   

I will get hold of some pure Sodium Chloride too,  as that won't have the Ferrocyanide in. 

Thanks again

Paul

[John Cuthber]

If someone thinks you need an MSDS for the stuff you put on your food, they have failed to understand risk assessment.

[exchemist]

1 hour ago, paulsutton said:

Thanks for this,  I have copper sulphate in with my chemistry kit,  so can give that a go.

I think i need to find a way to grow the initial seed crystal then.

I am about to start as a TA in a primary school.  There are various ideas here,  perhaps we can investigate as a class too.   It would need the usual risk assessment  though which is fine, as i can find the materials safety data sheets for everything.   

I will get hold of some pure Sodium Chloride too,  as that won't have the Ferrocyanide in. 

Thanks again

Paul

I think you just tease out the biggest crystal you can find - and then spend ages cursing and swearing as you try to tie it with a loop of cotton thread. Perhaps if you make a little slipknot you can tighten it around the crystal and trap it firmly enough to be able to suspend it. (I use slipknots at this time of year to tie the string round the paper and foil coverings over the Christmas puddings, before I steam them.🙂)

Edited December 3, 2021 by exchemist

[paulsutton]

On 12/3/2021 at 5:53 PM, John Cuthber said:

If someone thinks you need an MSDS for the stuff you put on your food, they have failed to understand risk assessment.

I was thinking more for the Copper Sulphate.    But I understand your point.

[paulsutton]

As an update to this,  I am repeating the original experiment with some lab grade Sodium Chloride.   This will hopefully generate some nicer cuboid crystals.  From there I want to try and look at obtaining a seed crystal and then growing from that. 

Also made sure the NaCl solution is saturated.  Will see what happens.

All fun stuff,   hopefully over time I can repeat with other solutions such as Copper Sulfate

 

Paul

[exchemist]

17 hours ago, paulsutton said:

As an update to this,  I am repeating the original experiment with some lab grade Sodium Chloride.   This will hopefully generate some nicer cuboid crystals.  From there I want to try and look at obtaining a seed crystal and then growing from that. 

Also made sure the NaCl solution is saturated.  Will see what happens.

All fun stuff,   hopefully over time I can repeat with other solutions such as Copper Sulfate

 

Paul

I suppose you can ensure the solution is saturated by having some free crystals at the bottom. But then I think you need to make sure your chosen seed crystal is the largest, as I seem to recall the largest one will grow at the expense of the smaller ones, due to it being fractionally more stable (more favourable ratio of stable sides to less stable edges).