[Tittywahah]

I have sodium silicate solution and use it no problem.  But I also have sodium silicate powder.  Now I have had this for a year and this was what I originally bought in order to make the solution in the first place.  The problem that I had was that it was completely insoluble in water.  Now this should not be, and so have kept it on my shelf untouched.  The company replaced it thankfully, but I am curious - has anybody any thoughts about this.  Are there any tests that I can do to establish what this product might be, or what may be wrong with it?  thanks. I am simply curious otherwise I will ditch it.

[billnotgatez]

I will as some of my pottery friends.

[Intanjir]

Sodium Silicate powder isn't completely dissolvable at neutral pH even at elevated temperature. While most of it should dissolve there will be a fraction which will not. I guess the formation of an insoluble fraction (sodium poor clumps?) is just an inevitable part of when they dry it into a powder. If you assess that it is insoluble by noting that even a small sample fails to completely dissolve then you might come to a mistaken conclusion. In addition, temperature is very important. I generally have to literally boil the sample to get it to really dissolve. The solubility is high, but it does not easily dissolve.

[Tittywahah]

Well this is a mystery.  I have not found One single place on the whlole of the web, from chemistry references to manufacturer's data to gossip column that says that sodium silicate behaves like this certainly no chemistry reference that I read boils the water, in fact there is one you tube that throws tons of the stufff into a beaker of water.  Quite the opposite both sodium silicate and the powder are VERY soluble in water, no need to heat.  So where do you get your information from please. If I put 10 grams of my powder crystals into 200 mls  water at 70c, about 0.5 to 1 gram dissolves.

[billnotgatez]

It would be interesting if you had time to boil the  a sample of the old stuff and see if it would dissolve.
My initial thought was that they sent you frit by mistake.

[Intanjir]

My information source is just personal experience. I ordered sodium silicate powder, it didn't fully dissolve, I boiled it briefly and then it almost entirely did. It is only natural. They dissolve it in the first place using high pressure to achieve even higher temperatures.

Sodium Silicate comes in varying ratios. I assume that powders with a higher sodium content enter solution much easier. However, the stuff I work with is low sodium(3.22 weight ratio). Also, you don't really want to boil it for any length of time or you form a film at the top, just bring it to an initial boil.
Anyways if you are trying a 10g sample at 70C it should be obvious that more than a gram was dissolving. Bringing it nearer to 100C just helps with the stubborn bits to get rid of cloudiness.
It is very soluble in water. I am able to make at least a 25% solution. This it what makes it 'highly soluble': having a high saturation concentration. However it takes some effort to get it dissolved in the first place. There is a difference between highly soluble and readily soluble and all sorts of sources regularly confuse the two.

Here is a link where someone on sciencemadness had a similar trouble, looks like he never tried anything above 60C and never had much success:
http://www.sciencemadness.org/talk/viewthread.php?tid=23937
Looks like he decided he had the anhydrous form and gave up trying to dissolve it. Is it possible you ordered the anhydrous powder? I would think it hard to find a supplier for that in the first place but that would certainly put up a huge fight going in to solution if that is what you have.

[Tittywahah]

Hi, Ok thanks for your kind response.  This morning I put 20mLs de-ionized water in a test tube and kept at boiling temperature.  Here are the results:
3.5g dissolved after 5 minutes; water reduced from 20mLs to 6mLs.  Therefore 3.5g dissolved in 6mLs Water.
This means that 58.5g would dissolve in 100mLs, (dissolving at 1g in 1.71mLs water).The CAS number and EC number indicate that my product is Silicic acid and Sodium, classed as sodium silicate.  There are no ratios given for sodium oxide to sodium silicate.  I have no idea what the molecular weight might be, certainly not 122g/mol as this is sodium silicate with a different CAS and constitution gathering by what I have read on industrial sites data.

So is there an interesting way to find out this ratio or the g/mol?  Otherwise I have no idea how concentrated my solution might be.  No good adding sodium silicate to a given amount of water until nothing more dissolves since this does not necessarily mean that I have a concentrated solution in this particular case, its density could still be below its potential.

If you have any thoughts on this would be pleased to hear.  Thankyou.

[Intanjir]

If your supplier can give you more information that might be the easiest thing to do.
If you want to determine it yourself it will not be easy.
I imagine these days professionals would just use their spectroscopes or something.

If you want to determine what your powder is gravimetrically then you need to determine the relative sodium, silica, and/or hydrated water content. You only need 2 of these.
I've never done any of this, and I do not for a second think it will be quite so simple as I describe to accomplish.

You could try and determine the sodium content by adding HCl to excess, waiting for all of the silica to precipitate and filtering it out and weighing the sodium chloride after boiling the filtrate. Be sure to wash every little bit of the sodium chloride from the precipitate into the filtrate. The excess HCl should boil off.
You might also try to do a titration of acid while paying attention to the pH. Determining the composition from this would require some theory on the behavior of silicic acid. Neutrality wouldn't quite correspond to each sodium being paired with a chlorine since the silicic would also contribute to acidity, still I suspect it would be a fine first approximation if that is all you need.

The water content is a bit harder. To determine the water content you might try to decompose the water out via heat from either the original powder or from the precipitate from the previous stage. I would not know what temperatures would be required here, probably fairly high for the sodium silicate powder. The precipitate might be a better choice, I dunno. The water has an easier time leaving if exposed on the surface so when they do careful gravimetry they may do 2 or 3 cycles of grinding it and heating it to expose the surface better. However silicates are fairly hard, not the easiest things to grind at home.

Anyways none of this is really worth it unless you intrinsically like doing the chemistry. Worst case find another batch out there that is better labeled. It isn't expensive.

[Tittywahah]

Thankyou for your helpful insights.  I will do the HCl test and see what develops.  The titration of silicic acid I would have to research a bit, as you say, but will do some reading on this.  I have sodium silicate solution and have been using that.  But you did not say, I am curious, what sort of solubility do you get with your product, are my solubility findings expected?  less than yours? regards.

[Intanjir]

Ok, after thinking about it a bit more in the shower it might not be so bad.

You can perhaps titrate acid into your sodium silicate solution until you hit neutrality and wait for the silica to precipitate and then measure the pH. The silicic acid should now be almost entirely gone so this should now correspond to the pH of a NaCl + HCl mixture, so you can determine the HCl content from just the pH. It might take some time for all of the silica to precipitate, heating might help, but either way you might be concerned about HCl vapor escaping and throwing off the measurement. So perhaps just stopper it up in a test tube and wait. This shouldn't be nearly as difficult since there is no filtration step. Anyways this process might be useful for me so thanks for prompting me to think about it!

Once you know the sodium to total ratio you might be able to find products out there with the same ratio and just suppose that you have a similar hydration ratio as them. Of course normally the ratio that is advertised on the front is the sodium oxide to silicon oxide ratio(fictitious of course since those species don't actually exist in the product)...

I never tried to make anything above a 25% solution, so I'm not really sure if I could get up to the 37% that you made.

[Tittywahah]

Hi, Sorry, can not see the connection between the PH of the HCl and NaCl and the NaO to sodium silcate ratio - you have lost me. Tried to get my head around this logic but falled.  Also If titrate the silicate solution with HCl until neutral? How can the solution ever reach neutral if I am adding HCl?

[Intanjir]

Sodium Silicate is basic in solution. It is the salt of a strong base(NaOH) with a weak acid(Silicic, Si(OH)4). You can neutralize it with the HCl. When you do so the lack of available hydroxides and sodiums will cause things to favor silica over silicic and this silica should almost all precipitate... possibly after some time. The goal is to use just a little bit more HCl than is needed to ensure that each Na has a Cl. So initially titrate down to a pH of 6 or so.

When almost all of the silica has precipitated you can measure the pH. Now that the concentration of silicic acid is negligible, any left over acid must just be that portion of hydrochloric which was in excess of what was needed to match the sodium hydroxide. So now knowing the volume and the pH you can just calculate this free hydrochloric fraction and now you have enough information to determine how many sodiums got neutralized.

So now you know the Sodium content of your sample, and of course you also know the original weight of your sample. So you can figure out the sodium oxide weight as a proportion of the total weight of your sample. This is 'fictitious' sodium oxide. It isn't really there as sodium oxide, but this is just how they report the constituents of sodium silicate. They view it as N(Na2O) M(SiO2) Z(H2O), for some N, M and Z.

Now at this stage you do not know the ratio of sodium oxide to silicon oxide. This is the headline ratio that is reported by the manufacturer. However you do know the % Na2O. So you can make the rash assumption that these things tend to dry with the same level of hydration. Take a look at this table:
http://www.pqcorp.com/Portals/1/lit/17-2b%20Solid%20Silicates%201-14.pdf
Generally it seems you have about 18% water in the various powders, unless you have an anhydrous powder.
Course that is from just one manufacturer, perhaps it varies afterall.

Anyways since you have solution of known ratio it would be a very good idea to first verify that this method of analysis works on the sample.

[Tittywahah]

Clear and concise, many appreciations. Thankyou. Can I use phenolpthalein in this titration.  Unfortunately my actual silicate solution also does not give away any info, even with the MSDS sheet I saw nothing. Nevermind.  Thankyou very much for the explanation and that link. Kind regards.

[Intanjir]

Sodium silicate will be crosslinked by all sorts of organic molecules. I think phenophthalein is typically dissolved in ethanol, and ethanol will definitely crosslink sodium silicate. There is a fun make your own bouncy ball demonstration people do with this reaction. Anyways you might be able to get it to work for your titration by diluting the indicator solution with water before adding it to the sodium silicate. However I think that if you just dropper in the pheno as is, the silicate will form a little hard crosslinked nodule on contact with the concentrated ethanol. Also diluting the sodium silicate solution a bit would increase the the proportion of monomer silicate which should help. However too much dilution would make the whole precipitation take longer.

Well since you don't have any of known composition I will try it out myself to verify whether it works soon. If it does then I can adapt it for something similar I am doing.

[Borek]

Sodium silicate will be crosslinked by all sorts of organic molecules. I think phenophthalein is typically dissolved in ethanol, and ethanol will definitely crosslink sodium silicate. There is a fun make your own bouncy ball demonstration people do with this reaction. Anyways you might be able to get it to work for your titration by diluting the indicator solution with water before adding it to the sodium silicate. However I think that if you just dropper in the pheno as is, the silicate will form a little hard crosslinked nodule on contact with the concentrated ethanol. Also diluting the sodium silicate solution a bit would increase the the proportion of monomer silicate which should help. However too much dilution would make the whole precipitation take longer.

1. You need just a drop of the indicator solution, that's way too low amount for any serious reaction between ethanol and silicate. Besides, bouncy ball is made of a dry silicate mixed with ethanol, not of silicate water solution.

2. Whether indicator works for acid-base titration (and titrating silicate with HCl is exactly this kind of titration), depends on the the indicator color change range and titration equivalence point. Phenolphthalein won't work here at all, methyl orange will.