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Specialty Chemistry Forums => Citizen Chemist => Topic started by: Tittywahah on March 27, 2014, 11:35:49 AM

Title: Test for sodium silicate
Post by: Tittywahah on March 27, 2014, 11:35:49 AM
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.
Title: Re: Test for sodium silicate
Post by: billnotgatez on March 27, 2014, 11:29:57 PM
I will as some of my pottery friends.


Title: Re: Test for sodium silicate
Post by: Intanjir on March 28, 2014, 01:54:02 AM
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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 28, 2014, 03:33:42 AM
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.
Title: Re: Test for sodium silicate
Post by: billnotgatez on March 28, 2014, 09:44:43 AM
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.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 28, 2014, 12:49:02 PM
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 (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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 29, 2014, 05:46:50 AM
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.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 29, 2014, 12:58:42 PM
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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 29, 2014, 01:25:12 PM
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.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 29, 2014, 01:39:19 PM
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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 29, 2014, 03:52:11 PM
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?
Title: Re: Test for sodium silicate
Post by: Intanjir on March 29, 2014, 05:14:51 PM
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 (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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 29, 2014, 06:43:38 PM
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.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 29, 2014, 08:40:37 PM
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.
Title: Re: Test for sodium silicate
Post by: Borek on March 30, 2014, 03:44:11 AM
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.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 30, 2014, 07:26:59 AM
Waiting for HCl at the moment so when that is ready I shall get to work on the above out of interest.  Though I will also use Phenolpthalein just to see what happens don't see any reason why it won't work being that it will turn from pink to colourless at a ph 8 then red below 7 theoretically. I've used it before many times in acid base titrations so do not see what the problem here would be. Can only experiment and if wrong will get back here and confess.

Edit:  This is from wiki answers, this guys explanation is unclear.  I wonder if you could explain it better.

"""""firstly, take 1ml of sodium silicate and add 99ml of water. titrate it with 0.5N HCl and use 1 drop phenophthalein as indicator. the amount of HCl used is converted to gram by using the density and molecular weight calculations.
1.177gm of HCl used for 1 gm of sodium oxide, calculate by multiplying your HCl used for your sodium oxide.

now take 10ml of silicate and weigh it in grams and heat it at 180 degrees celsius for 2 hours to get solid content (water evaporated)
deduct the value of sodium oxide from total solid content obtained.
this is the value of silica in your sodium silicate.""""""


1.calculate by multiplying your HCl used for your sodium oxide - I take this to mean that I should multiply the amount of titrant used by the density of the HCl to determine the grams used?  Thats fine, but what the hell does he mean by this - "used for your sodium oxide. "?
2.now take 10ml of silicate and weigh it in grams - I am dissolving the solid grams in water I then weigh the whole solution of water? The solid that is left is is then deducted from the original weight of the solution - this seems absurd to be honest since and completely incomprehensible.  Not to mention that the solid left over is still oxide and silica?

Can someone please make sense of this procedure. If I don't understand then it is because there is lack of clarification in this explanation.
Title: Re: Test for sodium silicate
Post by: Borek on March 30, 2014, 09:12:58 AM
I will also use Phenolpthalein just to see what happens don't see any reason why it won't work being that it will turn from pink to colourless at a ph 8 then red below 7 theoretically. I've used it before many times in acid base titrations so do not see what the problem here would be.

http://www.titrations.info/titration-end-point-detection

http://www.titrations.info/acid-base-titration-end-point-detection

and curve for silicate titrated with HCl against phenolphthalein:

Title: Re: Test for sodium silicate
Post by: Tittywahah on March 30, 2014, 10:43:04 AM
Hi Borek, does this horizontal axis indicate that between P 11. and 5 one is adding twice as much HCl again before the end point is visible?  If this is so - I have a special range of litmus paper that measures between 8 and 6.5 - I could also use this.  I suppose a bit of experimenting then I can learn for myself.  thankyou for that link by the way, useful reading as well.  I really don't need to do any of this, but I just have to, strange obsession this need to analyse and learn and know.
Title: Re: Test for sodium silicate
Post by: Borek on March 30, 2014, 11:14:03 AM
Hi Borek, does this horizontal axis indicate that between P 11. and 5 one is adding twice as much HCl again before the end point is visible?

Perhaps this is some limitation of my English, but I read what you wrote as "volume of the titrant added between 100% (pH 11.46) and 200% (pH 5.16) is two times larger than the volume added between 0% and 100%". No, these volumes are identical.

Quote
I have a special range of litmus paper that measures between 8 and 6.5 - I could also use this.

1. Titrating against pH strips , while possible in theory, in practice doesn't work that good.

2. Your strips won't work, you need an indicator that changes pH on the steep part of the curve, somewhere between 7 and 4. Otherwise your titration results will be quite erratic because you will have serious problems correctly - and reproducibly - detecting end point.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 30, 2014, 12:30:08 PM
Beautiful chart Borek =)
And yes from it I can see that methyl orange would definitely be the appropriate indicator to use thank you.

I agree that adding a drop of pure ethanol wouldn't hurt if the sodium silicate solution is sufficiently dilute. I think that adding to 1% would work, but at 10% I think it might make a nodule. I'll try it out later today out of curiosity.

All of the recipes I have seen for the bouncy ball have used the already dissolved sodium silicate.
I do not think the silicate powder will do much of anything at all if added to concentrated ethanol. At least not the stuff I have, it is hard enough just to get it to dissolve in water.

Since my product is well labeled I intend to cheat by just adding the amount of HCl I calculate will account for the Na, and using the pH meter to record the pH. I'll add some methyl orange too though.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 30, 2014, 12:50:45 PM
So the wiki answers answer appears to presume that you are starting with sodium silicate solution. So this explains second part where he has you dry it. He seems to think that 180 C for 2 hours is enough to get the anhydrous solid, and perhaps he is right. So you might try taking 3g or so of the powder and roasting it at 180C and see if you lose weight. If everything is in order then you should lose around 18% of the weight as you lose your waters of hydration. Anyways I read it here as him having you subtract the weight of sodium oxide content that you think there should be from the weight of the dried powder to get the weight of the silica which is of course fine.

The first part of the answer is interesting. He has you make a fairly dilute solution. I do not think any silica would precipitate at this dilution in the time frame of the titration. So you still have the silicate ions floating around lowering the pH a bit. However from looking at Borek's very helpful chart this is all perfectly fine. All we are after for the titration is finding the steep part of the pH curve, and this corresponds to having just enough HCl to account for each Na. I confess that I was making it all harder than it really had to be, since I had forgotten the importance of the knee in the titration pH curve. Borek's chart also suggests that pheno may just barely work as an indicator here, if you have a good enough eye to discern very pale magenta from perfectly clear. I am skeptical though.

By 'used for sodium oxide' he just means the conversion ratio for the weights assuming that 2 moles of HCl at the steep part of the titration curve corresponds to 1 mole of Na2O.
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 30, 2014, 06:34:54 PM
I was searching for the maths involving how to interpret the data from the titrations that we have been talking about.  From this source: The OxyChem Sodium Silicates Handbook, I found the following:

%Na2O = mLs HCl used x Molarity x 3.1/ sample weight

The only puzzling thing was the 3.1.  So I discovered this earlier on in the document where Baume is recorded with regards to temperature, there is a 3.0 and 3.2.  Now I have absolutely no idea what any of this means, and have probably assumed the connection between the 3.1 and this Baume to be the answer, but I think not.  Do any of you have a clue why the 3.1 is here?
Title: Re: Test for sodium silicate
Post by: Intanjir on March 30, 2014, 07:56:26 PM
3.1 = the molecular weight of Na2O(61.98) divided by 20.

You divide by 2 because it takes two HCl per Na2O, and you further divide by 10 because of the conversions from mL to L and to percentages(ie divide by 1000, and then multiply by 100).
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 31, 2014, 07:09:50 AM
So:   (mLs HCl/2) x M x (61.98/10)  Although why divide by 10 in the first place?  This is the same as the number of moles in 100 mLs, which makes no sense at all. Why do this?  The 61.98 is molecular weight per litre of one mole.  Why divide it by 10?


Edit:  Always do a balanced equation before titration:
Na2SiO3+2HCl=H2O+2NaCl+SiO2
Na2SiO3+2HCl=H2SiO3+2NaCl
the first one we have silicon dioxide precipitate (the Silica gel) and the second one we have the silicic acid but I am thinking that actually the the first reaction is the final one immediately after the second one has taken place because silicic acid loses water very quickly and becomes the gel of the first reaction equation.  Just wanting to be certain about my understanding.
Title: Re: Test for sodium silicate
Post by: Borek on March 31, 2014, 08:16:34 AM
Although why divide by 10 in the first place?

Have you read Intanjir post? He explained it quite precisely:

you further divide by 10 because of the conversions from mL to L and to percentages(ie divide by 1000, and then multiply by 100).
Title: Re: Test for sodium silicate
Post by: Tittywahah on March 31, 2014, 09:48:17 AM
I know that I dumb on the uptake here, ignorant of maths and can't get it because I am lacking in understanding where others take for granted - I am sorry. But I do not understand the principle here at work, why am I converting to Litres and then to percentages?  I see his answer but I can not understand the mathematical reasoning.  I know the 62g/mol is per litre and so this needs to be divided by 1000 to arrive at mol per mL as in other stoichemetry calculations, but to further multiply by 100 I do not understand. Sorry.

Title: Re: Test for sodium silicate
Post by: billnotgatez on March 31, 2014, 10:09:04 AM
@Tittywahah
Forum rules suggest you use appropriate editing to post things like formulas.
You can use the function bars above where you enter the post as well as other features.
You can select the Preview button before posting to make sure you got the editing correct.

For instance you could have posted your formulas this way
Na2SiO3+2HCl  :rarrow: H2O+2NaCl+SiO2
Na2SiO3+2HCl  :rarrow: H2SiO3+2NaCl


Title: Re: Test for sodium silicate
Post by: Tittywahah on March 31, 2014, 10:17:59 AM
Ok I stand corrected. Sorry.
Title: Re: Test for sodium silicate
Post by: Intanjir on March 31, 2014, 06:46:43 PM
The multiplication by 100 is simply to convert a fractional proportion into a percent, ie 0.75 is 75%.
Title: Re: Test for sodium silicate
Post by: Tittywahah on April 01, 2014, 05:10:29 AM
Thankyou. 
Title: Re: Test for sodium silicate
Post by: Intanjir on April 01, 2014, 07:44:37 PM
Ok, I did that titration of HCl into the sodium silicate with universal indicator and it changed color to orange within 5% of when you would expect it to given the concentration given on my stuff's label.
Title: Re: Test for sodium silicate
Post by: Tittywahah on April 02, 2014, 04:32:51 PM
Ok I did the titration and here are the results so far:
Adding phenolpthalein to the 5g Sodium silicate dissolved in water, it turned pink and was at a PH above 11
Using 0.5M HCl as the titrant and 5g sodium silicate dissolved, HCl added until pink disappeared and the PH strips measured below 6.8 (Strips range 0.3 increments;
Results after calculations: 0.93g Na2O this is 18.6% in this batch of powder

My other Sodium Silcate solution has 12% Na2O and 30% silicon dioxide at 1.5g per mL.

I will have to do the titration again tomorrow to be sure. I think I need to stop before the 6.8 is reached but also take a measurement both when the pink colour disappears and then when the PH is at 6.5.  we will see what the results are then.
Title: Re: Test for sodium silicate
Post by: Tittywahah on April 03, 2014, 08:37:06 AM
I knew I made a mistake yesterday, tiredness.  Did a comprehensive test this morning.

0.5M HCl (Density 1.18) added to 5g Sodium Silicate dissolved.

at 35mLs the phenolpthalein turned from pink to clear
at 39mLs  PH at 8.3 exactly
at 40mLs PH at 6.8 + precipitate began to form
at 42mLs PH at 1.0

Taking the value of PH 6.8 the Na2O content is at 0.62g per 5g which is 12.4%

Now attempting the Silicon Dioxide amount
Title: Re: Test for sodium silicate
Post by: Intanjir on April 03, 2014, 02:27:47 PM
12.4% Na2O seems low for a powder, might make some sense of why it was so stubborn to dissolve.
Hopefully you get at least 25% or so weight loss on roasting.
If you don't get any weight loss on roasting the powder then something is wrong, hehe.
Title: Re: Test for sodium silicate
Post by: Tittywahah on April 03, 2014, 03:18:12 PM
Yes, absolutely. It is actually crystaline and contains very very hard lumps which I have to break up.  Is it harmless to roast in the cooking oven?