Sciencemadness Discussion Board

Sodium Metasilicate

kazaa81 - 13-6-2006 at 15:57

Sodium Metasilicate Preparation

Sodium Metasilicate is the most stable of silic acid sodium
salts (ortho form isn't much) and can be prepared from molten or
hot aqueous NaOH and SiO2 (preferably in powder, so that
it has more reaction area).

Here I prefer use molten NaOH for not having the trouble of a bubbling
aqueous solution. This will lower the bubbling, but will not delete
it in absolute; if you heat your NaOH too much, it will bubble too.

A good container for this reaction is a steel crucible
(even mild-iron does), because everything made of glass, ceramic
or even quartz, isn't suitable for this reaction.
However, some types of ceramics could withstand molten NaOH,
but I wouldn't recommend this.

So, here we are using an improvised crucible made of steel.

The reaction is as following:

2 NaOH + SiO2 ----> Na2SiO3 + H2O
79,99 60,08 122,06 18,01

On this proportions, you can calculate the amount of NaOH and SiO2
needed, and also the yield based on amount of reagents.

For example:
- for every 1g of NaOH, you will require 0,751g of SiO2
- for every 1g of SiO2, you will require 1,331g of NaOH
- every 1g of NaOH will produce* 1,525g of Na2SiO3
- 1g of Na2SiO3 will be produced by 0,655g of NaOH*

*= if proper balanced by the amount needed of SiO2

Here is some data(1) about the substances we will handle:

Sodium Hydroxide
NaOH
CAS #: 1310-73-2
Mol. 39,997 g/mol
Form: white orthorhombic crystals; hygroscopic
M.P. 323°C
B.P. 1388°C
Density 2,13 g/cm^3
Soluble 100^25g in 100 ml H2O;
Soluble in EtOH, MeOH

Sodium Metasilicate
Na2SiO3
CAS #: 6834-92-0
Mol. 122,064 g/mol
Form: white amorphous solid; hygroscopic
M.P. 1089°C
Density 2,61 g/cm^3
Soluble in cold H2O; reacts in hot H2O

Silicon Dioxide
SiO2
CAS #: 14808-60-7
Mol. 60,08 g/mol
Form: colorless hexagonal crystals
M.P. trans to beta-quartz at 573°C,
to trydimite at 867°C
and to cristobalite at 1470°C
B.P. 2950°C
Density 2,648 g/cm^3
Insoluble in H2O, acids; soluble in HF

Practical

Reagents:
Sodium Hydroxide, NaOH, 10g
Silicon Dioxide, SiO2, 7,6g

Apparatus:
Steel crucible, small
Heating source, Gas (propane, butane) torch
Tongs that fits to the crucible

The crucible is loaded with NaOH flakes and quartz powder,
not necessairly intimately mixed.

The heat source is turned on, and the loaded crucible is put on it.
If you have a fitting-place for the crucible it's better, otherwise
you can use a pair of long tongs.
Be sure to make NaOH molten but not boil, since NaOH is quite
caustic and drops of NaOH aren't needed or wanted.

Maintain the heating for about 20 minutes, and the reaction must be
completed.

The water produced by the reaction is quite probably boiled away,
so it isn't really a problem; air vapor is much worse for hygroscopic
substances like NaOH and Na2SiO3.

We have used slightly more SiO2 than what needed, because it is more
easily to separate, since it's insoluble and won't remain in the products
as NaOH would likely to do.

Now, you can separate this by dissolving your sodium metasilicate in water,
making a water glass solution of variable strenght, or molten it and pour
somewhere. Be aware that Na2SiO3 is quite caustic also as NaOH, and hygroscopic
as well.

Now that you've made sodium metasilicate, you can do quite much things
with it, some examples are: make other metal silicates, make water glass and/or
silica gel (widely used moisture absorbing) or use it, very dilute in water,
as an aid for growing diatoms, radiolarians or others micro-organisms that
need silicium to build their shells.

References
(1) CRC Press, Handbook of Chemistry and Physics, 85th edition

This is an experiment I've done today. Pictures coming as soon as I get a camera. Feel free to post corrections and comments.

chromium - 14-6-2006 at 04:17

Useful prep especially for those who can not buy waterglass. (i can)

Some other uses:

Water glass can be used as glue. It can be used to make organic matter (for example wood surface or piece of cloth) less combustible. Water glass and acid put toghether make lot of white solid that turns quite hard after standing some time. This property can be used for rather cool demo experiment.


[Edited on 14-6-2006 by chromium]

kazaa81 - 14-6-2006 at 04:44

Some waterglass are just aq. sodium metasilicate, while others contains other silicates (potassium, for example) in it.

The thing you're mentioning, chromium, waterglass + acid, is quite surely silica gel, a form of active SiO2 which absorb moisture. I write "quite surely" because I don't know if the product varies about the acid used, however waterglass and HCl produces silica gel.

Also, Na metasilicate precipitates, more or less slowly, solid SiO2 upon certain conditions, and it is used to "glue" together glass (since glass is mainly composed of SiO2).

I've not encouraged the use of common glass crushed in the reaction, in place of quartz powder, because, other than some salts for dying it, common glass contains other oxides that makes the product not much clean.

[Edited on 14-6-2006 by kazaa81]

neutrino - 14-6-2006 at 14:32

Quartz powder... Common white sand, right? Even yellow sand shouldn't have a very high concentration of contaminants.

kazaa81 - 17-6-2006 at 07:04

yes, quartz sand it's common white sand.
Don't know about the purity of yellow sand; also, purity of a material can't be seen just by its color...a sand can be white if it contains quartz, but even if it contains pumice, so... :o
However, the thing that interest we in the experiment is just to use the purest possible SiO2...quartz is a pure form of it.
I've not encouraged to use glass because of the impurities previously mentioned

12AX7 - 17-6-2006 at 08:13

Erm, I posted about sand purity in here too, 99%+ is used for glassmaking for instance, but that post disappeared too. WTF?!

Tim

Polverone - 18-6-2006 at 10:26

Here's a PDF:

https://www.sciencemadness.org/member_publications/sodium_me...

I will add pictures when they become available.

12AX7, I don't know what is happening with your posts. I didn't catch your missing post in this thread, but I do remember seeing your long post on antimatter in the 1908 Siberian explosion thread. I checked the administration logs: no admin deleted your post. I also checked the database tables and no problems were found.

Rosco Bodine - 19-6-2006 at 23:11

Sodium metasilicate is an OTC item in hardware stores .

Red Devil " TSP-90 " is one example .
There are other brands and it is cheap .
Such cleaners are used as an environmentally friendly
substitute for TSP .

http://www.reddevil.com/pdfs/faq_0261.pdf

Also it is a great whitewall tire cleaner , an ingredient
in Westley's Bleche-Wite wheel cleaner .

The composition of water glass is different .

Silica gel ( kitty litter ) reacts more readily with lye
and in hot concentrated aqueous condition if you want to go the make your own route ( IIRC ) it has been a few years since I have done this reaction , as opposed
to using sand which is less reactive and requires more
extreme conditions . This would need to be rechecked
because it was over twenty years ago and I don't clearly
remember the experiment . But as IIRC you can dissolve
silica gel in strong hot aqueous alkali , and upon addition
of an acid the silica gel ( colloidal silicic acid ) is precipitated again .

Water glass is available in different compositions with
regard to the sodium content and level of hydration ,
and it is different in chemical composition from the detergent use sodium metasilicate .

EDIT : I just found something interesting on an MSDS
warnings section on reactivity hazards , that is a new one on me ..... and quite intriguing actually ,

" Upon contact with sugars, the sodium metasilicate may react to form deadly carbon monoxide gas. "

Might make for some interesting experiments which could
reveal usefulness potential for the metasilicate as an
oxidizer for organic materials ????? :o:D

If this is correct , then there is analogous behavior for
the metasilicate and hypochlorite ? ( which would do
a lot for explaining the bleaching effect of the tire cleaner
for example )

Where do they come up with this stuff ?

http://www.alken-murray.com/874msd.htm

see item # 10 down the page

Curiously , whenever using the tire cleaner , I have often
noticed a distinct smell of methylamine emanating from the
surface of the tire being contacted by the cleaner .
So it would seem a bit more of methylamine can be gotten
from kitty litter , lye , and an old tire ......once the
optimum reaction conditions are identified for the " stew " :D


[Edited on 20-6-2006 by Rosco Bodine]

kazaa81 - 19-6-2006 at 23:53

Quote:
Originally posted by Rosco Bodine
Sodium metasilicate is an OTC item in hardware stores .

Here it's not avaible, unluckily...
Quote:
Originally posted by Rosco Bodine
This would need to be rechecked
because it was over twenty years ago and I don't clearly
remember the experiment . But as IIRC you can dissolve
silica gel in strong hot aqueous alkali , and upon addition
of an acid the silica gel ( colloidal silicic acid ) is precipitated again.


I think you don't want to start with silica gel, if you're synthetizing sodium silicate to then produce it! :D
Also, the sand I used isn't just "sand"...it's pulverized quartz, really pure SiO2!

Thanks for comments

Rosco Bodine - 20-6-2006 at 00:02

Actually there are times when you may want to change the form of dehydrated lumps of silicic acid to a dispersed
hydrated form of the same , and reprecipitation is a quick way to do that ......correct ?

Cabosil would do nicely too , or possibly even diatomaceous
earth .

[Edited on 20-6-2006 by Rosco Bodine]

Aqua_Fortis_100% - 12-10-2007 at 11:03

Some hours ago I've tried this procedure, but replacing quartz with powdered glass from a cup which coincidently broke yesterday..

65g of powdered glass(take in excess) were mixed with 100g of 60-70% pellets of white caustic soda and heated in a tomato can with an improvised alcohol burner.. good stirring was done (with an old teaspoon) and this was heated for 50 minutes..

Initially , all solids melted , gaving a white melt , and after 15-20 mins, started to changing in color..first pinkish ,and then white orange and finally red , like the tomato extract from the tomato can :o ..and started to bubble more and more, so I had removed from the fire..

After, with care, added slowly and with agitation water to hot melt which boiled very vigorously... Then passed this solution in a cloth (synthetic cloth) to filtrate the unreacted glass, and washed on filter to remove the last traces of the reddish substance.. at all, ~600mL of water were used.

after, I poured this in an plastic container and , while hot , added muriatic acid, and this gave a reddish ppt ..

but I have many doubts.. first, why both the melt ,solution and the precipitate turned red? maybe some iron corrosion in the can (?) and also the Fe++ ions on impure HCl (?), and also glass impurities (?)

BTW, what the advantages of producing silica gel using cold solutions instead of hot ? (as in frogfot page : http://www.frogfot.com/synthesis/silicagel.html )

I'm greatly interested in making my own silica gel, since I cann't buy this thing here..

thanks

[Edited on 12-10-2007 by Aqua_Fortis_100%]

not_important - 12-10-2007 at 17:49

I believe that cold, not too concentrated solutions give a better 'gel' or a higher percentage of it, while hot concentrated solutions give lower surface area powdered silica than hydrated gel.

Sounds like you managed to grab some iron, much of which tagged along with the SiO2. Common glass is soda-lime glass, about 60-75% silica, 12-18% soda (Na2CO3), and 5-12% lime (CaCO3) with traces of manganese and other colour modifiers; note that carbonates decompose during the making of the glass.

One possible OTC source for silica gel is the form used for drying flowers and so on - http://www.silicasec.co.uk/ Craft supply stores might stock it.

chemrox - 12-10-2007 at 21:05

Quote:
Originally posted by kazaa81
yes, quartz sand it's common white sand.


Not so! Common white sand is largely feldspar. Feldspars contain silica in different proportions and alkali metals and often Ca. Quartz sand is a particular kind of white sand that has a *high proportion* of qtz. The more "mature" sands have higher proportions of qtz because qtz is more mechanically and chemically resistant to weathering than the feldspars and other silicate minerals. Zeolites are some of the most susceptible and are thus hardrer to find. They are usually mined from areas affected by hydrothermal activity.

kazaa81 - 20-10-2007 at 14:58

Quote:
Originally posted by chemrox
Not so! Common white sand is largely feldspar. Feldspars contain silica in different proportions and alkali metals and often Ca.


look how I continued in the same post you've quoted...
Quote:
Originally posted by kazaa81
yes, quartz sand it's common white sand.
Don't know about the purity of yellow sand; also, purity of a material can't be seen just by its color...a sand can be white if it contains quartz, but even if it contains pumice, so... :o


So clearly enough, I wasn't saying that any white powder nor that every common sand is silicon dioxide and hence useful as a reagent in that preparation...next time check better, ok? ;)

12AX7 - 20-10-2007 at 17:03

One FYI: a local sandstone series (in the St. Peter formation) consists of very high purity, well rounded, loosely bonded quartz grains. A theory is that it formed from the decay of earlier Cambrian sandstones, which are famously iron colored (see: Wisconsin Dells). It is said that, in areas where it is exposed, since it is so weak, it can be mined with a pick and shovel and, because it is so pure (>98%), is directly suitable for producing glass.

Sandblasting sand, around 50-100 mesh, white granular silica/quartz sand, is similarly good.

Most any sand is probably in the range of 90% silica. There aren't many minerals as resilient as quartz. Incidentially, feldspar easily weathers to kaolinite and similar clay minerals, which are washed downstream of the heavy quartz grains.

Tim

chemkid - 20-10-2007 at 19:51

Silica gel is also found in little packets that come with shoes, musical instruments and a variety of other items. However the silica gel i removed from these was green. Any ideas?

Chemkid