Sciencemadness Discussion Board

Red Material?

Agari - 8-10-2015 at 15:03

I was making silicon tetrachloride using the following method:
-Added around 75 grams of crushed up TCCA pool tablets to a 3-neck flask and sealed one of the necks.
-Attached an addition funnel with a mixture of 50 milliliters of hydrochloric acid and 50 milliliters of water.
-I then connected the final neck of the flask to a test tube full of concentrated sulfuric acid using plastic tubing.
-I then connected the test tube with acid to a reaction tube with 12 grams of somewhat dry silicon powder inside.
-The reaction tube was then connected to a water-cooled condenser,which in turn was connected to another 3-neck flask placed in an ice bath,with one end being connected to an inverted-funnel trap in hydrogen peroxide.
-I then opened up the stopcock on the addition funnel,which then caused the HCl-water mixture to enter the flask with the TCCA inside and hopefully generate chlorine.
-I started heating the reaction tube with a blowtorch,and I could see that the silicon powder began to glow at seemingly random locations and traces of green gas(chlorine) inside the tube.
-After some time, I started heating the top of the tube.
In the end,the vapor that came over into the condenser turned a red-ish color,with some clear liquid dripping into my collecting flask.
In the end,my final product was a collecting flask with a red liquid inside,so the question is:What is the red liquid that ended up in my collecting flask? As far as my knowledge goes,silicon tetrachloride is colorless.

[Edited on 8-10-2015 by Agari]

Oscilllator - 8-10-2015 at 16:18

Nice Experiment Agari.
Is it possible that there were sulfur impurities in your silicon? If so, it is possible that you produced some sulfur dichloride, which is a red volatile liquid.

Agari - 8-10-2015 at 16:34

Quote: Originally posted by Oscilllator  
Nice Experiment Agari.
Is it possible that there were sulfur impurities in your silicon? If so, it is possible that you produced some sulfur dichloride, which is a red volatile liquid.

If I were to compare the look of the liquid to something we can all relate to,I would say that it looks like a strawberry smoothie and is rather opaque,and not a transparent liquid. But let's assume that it is sulfur dichloride,will vacuum filtration or sep-funneling isolate the silicon tetrachloride?

[Edited on 9-10-2015 by Agari]

blogfast25 - 8-10-2015 at 16:47

Very nice experiment indeed, Agari. Of the kind we could do with many more over here. But a picture tells a thousand words, though (in addition to your good write up).

The red must almost by definition be caused by some impurity in your silicon, and as Oscillator said sulphur is a contender here.

Do you have any idea of the purity of your silicon powder or its provenance? It's easier to purify something if you know what the impurity might be.

Agari - 8-10-2015 at 16:55

Quote: Originally posted by blogfast25  
Very nice experiment indeed, Agari. Of the kind we could do with many more over here. But a picture tells a thousand words, though (in addition to your good write up).

The red must almost by definition be caused by some impurity in your silicon, and as Oscillator said sulphur is a contender here.

Do you have any idea of the purity of your silicon powder or its provenance? It's easier to purify something if you know what the impurity might be.



Pic related:the collecting flask separate from the main setup,cropped out the unnecessary parts

WTF.jpg - 121kB

j_sum1 - 8-10-2015 at 17:10

Going out on a limb here. The sulfuric acid is to dry the chlorine, right? How likely is it that your gas picked up something at this stage?

Agari - 8-10-2015 at 17:17

Quote: Originally posted by j_sum1  
Going out on a limb here. The sulfuric acid is to dry the chlorine, right? How likely is it that your gas picked up something at this stage?

Well,I would say that the most it could pick up is either water between the sulfuric acid flask and the collector or,as others are theorizing,possibly sulfuric acid,I did not monitor the conditions within the system,obviously. When I separated the condenser from the reaction tube, a white gas came out,probably chlorine and SiCl4.

[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

blogfast25 - 8-10-2015 at 17:19

Things to look out for are tubing, connectors, sealing grease or seals that might react with chlorine and contaminate your SiCl<sub>4</sub>.

blogfast25 - 8-10-2015 at 17:21

Quote: Originally posted by j_sum1  
Going out on a limb here. The sulfuric acid is to dry the chlorine, right? How likely is it that your gas picked up something at this stage?


Using conc. H2SO4 to dry something like Cl<sub>2</sub> is fairly standard and should not be problematic. Cough.

100PercentChemistry - 8-10-2015 at 17:30

I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

blogfast25 - 8-10-2015 at 17:33

Quote: Originally posted by 100PercentChemistry  
IIt could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.


Siloxanes are colourless too.

100PercentChemistry - 8-10-2015 at 17:33

I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

Agari - 8-10-2015 at 17:33

Quote: Originally posted by 100PercentChemistry  
I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

In either case, what should I do to separate the silicon tetrachloride from the rest of the product? Will a simple distillation work? Do I need to vacuum filter or use a sep-funnel?

j_sum1 - 8-10-2015 at 17:34

Quote: Originally posted by blogfast25  
Quote: Originally posted by j_sum1  
Going out on a limb here. The sulfuric acid is to dry the chlorine, right? How likely is it that your gas picked up something at this stage?


Using conc. H2SO4 to dry something like Cl<sub>2</sub> is fairly standard and should not be problematic. Cough.

I was not really questioning the procedure. More the possible issues of contaminants (source of sulfuric acid?), plastic hose, rubber bung and any interactions these may have with either Cl2 or the acid. I was also throwing out a wild stab as to whether drying the chlorine was completely necessary in this case. If you removed this step and the problem resolved, you would have isolated the cause. Thus far in the thread no one had mentioned the drying stage.

Sorry for not explaining myself clearly. [offers blogfast a tissue for his cough]

[edit]
Quote: Originally posted by 100PercentChemistry  
I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

And there is the answer on why it is necessary to dry the chlorine. Ignorance fought.

[Edited on 9-10-2015 by j_sum1]

Oscilllator - 8-10-2015 at 17:35

The fact that your product is cloudy means that the impurities are solid (barring emulsion silliness). Since silicon tetrachloride has a very low boiling point, I would suggest gently re-distilling it. This has a very good chance of removing the red contaminant, and you can then easily conduct tests on it to determine its nature.

blogfast25 - 8-10-2015 at 17:36

Quote: Originally posted by Agari  
Quote: Originally posted by 100PercentChemistry  
I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

In either case, what should I do to separate the silicon tetrachloride from the rest of the product? Will a simple distillation work? Do I need to vacuum filter or use a sep-funnel?


Distillation would probably work, since as much of the impurity is present as a solid but as you know SiCl<sub>4</sub> is very sensitive to water, so you need to use quite dry equipment.

I do think we should continue to try and find the root cause of the contamination. That makes good science.


[Edited on 9-10-2015 by blogfast25]

100PercentChemistry - 8-10-2015 at 17:37

I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

Agari - 8-10-2015 at 17:41

Quote: Originally posted by blogfast25  
Quote: Originally posted by Agari  
Quote: Originally posted by 100PercentChemistry  
I can't find much. The silicon tetrachloride is not red. It could either be impurities, or a siloxane. Silicon tetrachloride reacts with water to form those.

In either case, what should I do to separate the silicon tetrachloride from the rest of the product? Will a simple distillation work? Do I need to vacuum filter or use a sep-funnel?


Distillation would probably work, since as much of the impurity is present as a solid but as you know SiCl<sub>4</sub> is very sensitive to water, so you need to use quite dry equipment.

I do think we should continue to try and find the root cause of the contamination. That makes good science.


[Edited on 9-10-2015 by blogfast25]

The concentration of the sulfuric acid is around 85%(rough estimate) and approximately 35% for hydrochloric,but I can't think of much that could contaminate the result. I should note that I saw a white gas inside the reaction tube at the beginning of the experiment,and I know that Chlorine is yellow-green,but i think the white is either sulfuric acid or water vapor,so I will accept that it could be sulfur dichloride.

[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

blogfast25 - 8-10-2015 at 17:44

Quote: Originally posted by j_sum1  

And there is the answer on why it is necessary to dry the chlorine. Ignorance fought.

[Edited on 9-10-2015 by j_sum1]


Yes, it would be folly to try such direct chlorination reactions with moist chlorine.

100PercentChemistry - 8-10-2015 at 17:45

I found the video form of your method. I am still looking... https://m.youtube.com/watch?v=wU77anzCzxg



It's probably sulfur dichloride. Most siloxanes are colorless.

[Edited on 9-10-2015 by 100PercentChemistry]

Agari - 8-10-2015 at 17:47

Quote: Originally posted by 100PercentChemistry  
I found the video form of your method. I am still looking... https://m.youtube.com/watch?v=wU77anzCzxg

I actually did the experiment based on Nile's video,I thought SiCl4 might be a useful reagent,though altered the quantities and possibly concentrations,still got red liquid.Yes yes,I know that I am a "scrub" for following it word-for-word.

Any future way to prevent contamination? I am planning on using the method in the video to make some more tetrachloride,and apparently all I had to do was filter it with cotton.

While we are on this thread,what could SiCl4 be used for as a reagent to synthesize something that can reasonably be made at home?



[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

[Edited on 9-10-2015 by Agari]

Removing the red

100PercentChemistry - 8-10-2015 at 17:57

Nile red's video says "I'm not sure what the red stuff is, but it's in a suspension, so it can be filtered away".

Agari - 8-10-2015 at 17:58

Quote: Originally posted by 100PercentChemistry  
Nile red's video says "I'm not sure what the red stuff is, but it's in a suspension, so it can be filtered away".

Well,since I already got the red as my final product,I would want to isolate it as well and probably store it if possible. Yeah,seems like I had to use cotton,just watched the very end.
Now that the problem is sovled,maybe one of us should drop a comment on Nile's video,even though he is unlikely to see it.

Is the chlorine generated from TCCA according to this equation: 3HCl + C3Cl3N3O3 = 3CNOH + 3Cl2?
Where the byproducts are chlorine and cyanic acid?


[Edited on 9-10-2015 by Agari]

blogfast25 - 8-10-2015 at 18:23

In the case of 'Nile Red's' video the red contamination is almost 100 % due to reaction of chlorine or SiCl<sub>4</sub> with the sealant at the entry and/or exit of the reaction tube. Using rubber/plastic at these points, especially the exit, is really asking for trouble: use glass or teflon joints there.

Nile Red' would also have done better to start heating at the left hand side of the Si, then gradually move heat (burner) to the right, to get much higher yield. Doing so would exploit the considerable heat of reaction to heat the silicon to the right of the reaction front. Despite those flaws it's a nice experiment.

[Edited on 9-10-2015 by blogfast25]

Agari - 8-10-2015 at 19:03

Quote: Originally posted by blogfast25  
In the case of 'Nile Red's' video the red contamination is almost 100 % due to reaction of chlorine or SiCl<sub>4</sub> with the sealant at the entry and/or exit of the reaction tube. Using rubber/plastic at these points, especially the exit, is really asking for trouble: use glass or teflon joints there.

Nile Red' would also have done better to start heating at the left hand side of the Si, then gradually move heat (burner) to the right, to get much higher yield. Doing so would exploit the considerable heat of reaction to heat the silicon to the right of the reaction front. Despite those flaws it's a nice experiment.

[Edited on 9-10-2015 by blogfast25]


Well,we should drop a comment on his video lol.
Is the chlorine generated from TCCA according to this equation: 3HCl + C3Cl3N3O3 = 3CNOH + 3Cl2?

blogfast25 - 9-10-2015 at 06:03

Quote: Originally posted by Agari  


Is the chlorine generated from TCCA according to this equation: 3HCl + C3Cl3N3O3 = 3CNOH + 3Cl2?


http://www.sciencemadness.org/talk/viewthread.php?tid=9713#p...

Boffis - 9-10-2015 at 10:03

The most likely impurity in lab grade silicon powder is iron. Ferric chloride is fairly volatile I would probably produce a dark brick red or brown colouration.

blogfast25 - 9-10-2015 at 10:21

Quote: Originally posted by Boffis  
The most likely impurity in lab grade silicon powder is iron. Ferric chloride is fairly volatile I would probably produce a dark brick red or brown colouration.


Sounds like a lot of iron to me going by these quantities of impurity in his product, also anh. FeCl3 is apparently almost black.

gdflp - 9-10-2015 at 10:28

Quote: Originally posted by blogfast25  

Sounds like a lot of iron to me going by these quantities of impurity in his product, also anh. FeCl3 is apparently almost black.

It is, or at least the material I have is. I suppose it could be classified as an extremely dark yellow/brwon, but it's definitely not a red color like that.

Praxichys - 9-10-2015 at 10:39

FeCl3 could be soluble in SiCl4, potentially making a red solution.