Sciencemadness Discussion Board

Reagent Density issue, what factors can influence changes in density in a normal lab setting?

FireLion3 - 1-7-2014 at 18:21

Typically when I purchase reagents the easiest method to verify the liquid ones is through a simple density test.

I got a simple compound today and the density keeps showing to higher than what it should be. Is there any reason this could happen? The variation is too big to for slight measurement error. I confirmed this on two different scales and in two different glass beakers.

Did I simple receive the wrong compound from my supplier?

I'm about to go do a boiling point test to see what comes up


[Edited on 2-7-2014 by FireLion3]

gdflp - 1-7-2014 at 18:57

What compound is it and how are you measuring the liquid volume? If you are doing it in glass beakers, then these can have a 5-10% error in the volume. I would use a volumetric flask or if not that then a graduated cylinder. My guess is that for such a small variation, this is just measurement error. Does the compound have any other defining characteristics like a smell, color, or specific reaction?

FireLion3 - 1-7-2014 at 19:01

The compound is supposed to be Anisole (methoxybenzene). The only reason I was relying on a density test is because with these beakers, about 10 other compounds with known densities that I had tested, came out nearly perfectly where they should be with the densities that I measured, so it wouldn't make sense for this compound to be so off. This density should be roughly 0.995.... yet the density I am getting after several tests is around 1.15-1.2.

Dr.Bob - 2-7-2014 at 07:37

I have used density a few times for a spec, but you really need a volumetric flask for the test be accurate, as the meniscus can change a lot with each compound, so beakers are not good enough. If you put 10 ml in a volumetric and have a 1 mg balance, you should get a number within +- 0.01 g/ml of the reported density. You could check the bp of it as well.

That density (if correct) is way too high to be anisole, but is closer to a halogenated or multiply methoxylated anisole. However, to complain to a supplier that a chemical is incorrect you really need more analytical data than just a crude density.

ScienceHideout - 2-7-2014 at 10:26

Before massing the reagent, make sure that everything is at a standard temperature. I believe the CRC handbook shows the densities of reagents at 25 degrees. If your room is a different temperature, you may be in trouble. Try the following... This is what I do for my gravimetric analysis.

First, let your balance warm up for approx. 10 minutes.
During this time, put the chemical in a water bath at 25 degrees.
Calibrate the balance.
Measure the empty cylinder/volumetric flask's mass 5 times, putting it on the balance, taking it off, taring, putting it on, off, tare, etc.
Write down the average mass of the vessel. DO NOT SIMPLY TARE IT! The balance could drift while taring it.
Fill the vessel with the chemical that was brought to 25 degrees.
Put it on the balance, again, 5 times, and record the average.

FireLion3 - 2-7-2014 at 17:19

I checked, the density is definitely way off.

I checked with the supplier and they informed me that the purity of what I ordered was 99.1%, which could account for the inaccurate density. They said they will have their manufacturer check on the batch and see what results they come up with.

Though I am still bothered in that I attempted to brominate the ring with Oxone and NaBr. This reaction is supposed to take 10 minutes to finish completion in water with Anisole, at room temperature, to yield a clear to slightly yellowish product. Yet I had it stirring for nearly an hour at 50-60 degrees and there was a very red organic layer at the bottom. Either indicating unreacted bromine, or some red [major] by product. This simple reaction cannot really generate many by products so I am extremely unsure about what I got. I am skeptical this is even an aromatic. This is even more odd seeing as I only added about 3/5 of my total oxone because there was still very large amounts of red organic globs in there. I didn't even bother to finish the reaction. There should have been plenty of remaining anisole in there to rapidly react with the bromine, but the red color was not showing any reduction at all.

Something was very odd about this because when I added it to water, about 95% of it sunk to the bottom, while about 5% of it left a noticable clear organic layer at the top. Though, hardly any at all, very very minor little groupings of organic bubblies at the top. Not enough to cover the entire top of the water. I am skeptical as to why this could happen.


[Edited on 3-7-2014 by FireLion3]

ScienceHideout - 2-7-2014 at 17:53

"I am skeptical this is even an aromatic"

I know that it is a sin to even think about lighting precious reagents on fire, but don't aromatic compounds always produce copious smoke from incomplete combustion? Perhaps you should give a bit of thought into lighting a bit of it on fire.

Another test for aromatics is the Friedel Crafts test if you are feeling less destructive.

Does the chemical in question even smell like anisole?

forgottenpassword - 2-7-2014 at 18:08

What was the boiling point?

Dr.Bob - 2-7-2014 at 18:58

Quote: Originally posted by FireLion3  
I checked, the density is definitely way off.

I checked with the supplier and they informed me that the purity of what I ordered was 99.1%, which could account for the inaccurate density.


It would take an 1% impurity of lead tetraethyl to change the density that much. My guess is that they bought it from China, and that means that they have no idea what is in it. An NMR or GC MS would be the best way to test it, but that is not trivial. But even a TLC would help determine if it is one compound or more.

FireLion3 - 2-7-2014 at 22:03

Quote: Originally posted by ScienceHideout  
"I am skeptical this is even an aromatic"

I know that it is a sin to even think about lighting precious reagents on fire, but don't aromatic compounds always produce copious smoke from incomplete combustion? Perhaps you should give a bit of thought into lighting a bit of it on fire.

Another test for aromatics is the Friedel Crafts test if you are feeling less destructive.

Does the chemical in question even smell like anisole?


I don't know what Anisole smells like. I did try heating it. I had my digital hot plate turned up to 280 degrees... when it got to 280 degrees it started very slightly boiling, but it was smoking far more than it was refluxing. Copious amounts of smoke is right. 280 degrees is not what it was boiling at, but that was the temperature of my hotplate. I didn't have any thermometers around to test the internal temperature.
Quote: Originally posted by forgottenpassword  
What was the boiling point?


No idea, see above.
Quote: Originally posted by Dr.Bob  
Quote: Originally posted by FireLion3  
I checked, the density is definitely way off.

I checked with the supplier and they informed me that the purity of what I ordered was 99.1%, which could account for the inaccurate density.


It would take an 1% impurity of lead tetraethyl to change the density that much. My guess is that they bought it from China, and that means that they have no idea what is in it. An NMR or GC MS would be the best way to test it, but that is not trivial. But even a TLC would help determine if it is one compound or more.


Could lead tetra ethyl even be an impurity in this? I'm thinking they may have just sent me the wrong product by mistake. I order from this company quite often (they are a chemical manufacturing plant). In the past they have always been very transparent and able to supply freshly updated COA's, and even give information about what the impurities are based on how the compound was synthesized or extracted. Typically they are byproducts from the synthesis... but I can't think of anything that would have such density.

Depending on how the compound was made, the impurity could be a polymerized by product. That wouldn't require any metal and the density could easily be twice the product.... though there would still need to be quite a bit to give product the raise that I measured.

Hopefully my measurement was just off. I just today ordered a glass syringe with 1/2 cc increments, to hopefully allow me to get an accurate measure of the density. I have a 0.001mg scale to go along with this, so this should reveal some results.

In any case, I am long time customers of this company so they would hesitate to resend my entire order for free if I truly felt it was wrong. They are looking into the matter.

[Edited on 3-7-2014 by FireLion3]

forgottenpassword - 3-7-2014 at 01:20

Do you have TLC plates?
From here: http://www.oc-praktikum.de/nop/en/instructions/pdf/1035_en.p...

The Rf for anisole on silica gel plates with 9:1 heptane : ethyl acetate is 0.84.

To determine the boiling point you should perform a simple distillation and record the vapour temperature of the distillate. If, as it seems, you are unable to do that: does your 'anisole' form the lower layer when added to water? If it does not then your density measurement is clearly in error.


[Edited on 3-7-2014 by forgottenpassword]

ScienceHideout - 3-7-2014 at 05:52

I believe that anisole is supposed to smell like anise, which I have always compared to black licorice. My aunt comes from Holland and she uses anise ALL the time in her cooking. I love her anise cookies :)

FireLion3 - 3-7-2014 at 12:20

Quote: Originally posted by forgottenpassword  
Do you have TLC plates?
From here: http://www.oc-praktikum.de/nop/en/instructions/pdf/1035_en.p...

The Rf for anisole on silica gel plates with 9:1 heptane : ethyl acetate is 0.84.

To determine the boiling point you should perform a simple distillation and record the vapour temperature of the distillate. If, as it seems, you are unable to do that: does your 'anisole' form the lower layer when added to water? If it does not then your density measurement is clearly in error.


[Edited on 3-7-2014 by forgottenpassword]


When I pour it in water it behaves strangely. 95% of it sinks to the bottom layer, are a relative pace, not super fast, but not super slow either, very indicative of similar, yet different densities. But, there is about 5% oily layer that stays on the top. To which I am skeptical of.

When I do heat it, it starts to smoke before it starts to boil. As in, the vapor also smells of smoke rather than the chemical smell. After it starts refluxing and I recool it, the entire mix turns yellow, indicating some sort of decomposition, but I am not sure of what.
Quote: Originally posted by ScienceHideout  
I believe that anisole is supposed to smell like anise, which I have always compared to black licorice. My aunt comes from Holland and she uses anise ALL the time in her cooking. I love her anise cookies :)


I don't know what anise smells like but I don't think this smells like licorice. It has somewhat of a chemically smell, not too different from Toluene, but a little less intense.

ScienceHideout - 3-7-2014 at 19:57

If it doesn't smell anything like licorice, then I would doubt that it is real anisole. Everywhere I can find says anisole smells like anise...

FireLion3 - 3-7-2014 at 22:40

Quote: Originally posted by ScienceHideout  
If it doesn't smell anything like licorice, then I would doubt that it is real anisole. Everywhere I can find says anisole smells like anise...


Well I can't really say it doesn't smell like licorice. The only licorice I've ever smelled is the candy twizzlers... and that's not even "real". They don't smell like anything... candy... artifical flavor?

Whatever the odor is, it is not one I deem pleasant. Having the bottle sit outside the confines of my lab very quickly produces an odor in the air only describable as "chemicals", but it doesn't smell too industrial. Could smell flowery I suppose. I am not sure. My sense of smell is not amazing.

[Edited on 4-7-2014 by FireLion3]

PHILOU Zrealone - 4-7-2014 at 07:20

Reaction of anisole with dry HCl gas should lead to a splitting into gaseous CH3Cl and phenol...
C6H5-O-CH3 + HCl --> C6H5-OH + CH3-Cl

Alternatively you can nitrate it with HNO3/H2SO4 to mono, di and trinitranisole.

Dr.Bob - 7-7-2014 at 12:55

My point was that no normal organic impurity could change the density that much with a 1% impurity. The material has a density consistent with a halogenated compound. The density of a compound is related to the elements contained within, and even if a hydrocarbon polymerizes or rearranges, the density of the product will be related to the elemental composition. So to have a density of 1.15 it would likely need to contain a halogen or some other element with a higher atomic number than C, H, O, or N, compared to anilsole and most other similar aromatic compounds, which mostly have densities at or below 1.00.

Ascaridole - 7-7-2014 at 15:13

I'm not 100% sure but I remember anisole having a b.p. below 200ºC, like in the 150ºC range. Wikipedia says 154ºC but I'd double check that.

Also if it is forming three phases in water something is wrong. Have you tried taking the lower phase running your bromination and taking the upper phase and running your bromination?

If one of them does work that may be your anisole. Take that phase and cleave the ether as PHILOU Zrealone said with HCl or you can use aq. HBr if you have some. Then do a FeCl3 test for phenol. The phenol should complex the Fe3+ and turn purple? Think it was purple/violet. Check the literature for TLC stains for phenols.

Even then thats not 100% proof thats your anisole, fractional distillation with close monitoring of the temperature and either GC/NMR/FTIR or at the very least UV absorbance test will give you more confidence that it is your anisole.

On a safety note if your anisole really is contaminated with an unknown treat it like its the plague. No telling what kind of heavy metal or halogenated organics may be in there. Seriously treat it and all waste like its the plague. Might just be oil or something innocuous but better safe than six feet under.

I know it cost more money but time is precious and paying for the EMD Merck or JT Baker stuff is worth it.

HgDinis25 - 7-7-2014 at 15:56

C'mon you're using BEAKERS for density tests, what did you expected? You probably could't tell mercury and water appart using those (irony but you get the point)!
Use volumetric flasks in all density measurments and I bet you're results will come along fine.

Ascaridole - 8-7-2014 at 00:57

HgDinis25 does have a very good point. Beakers are about +/- 5-10% or even more depending on volume and make. Also glass syringes are not typically calibrated for "To Deliver" so that may not solve your problem. Not saying you couldn't calibrate it your self. Besides you want to measure a big volume so the inaccuracy of your balance becomes insignificant. Hehehe relative percent error and propagation of error because any measurement is meaningless without knowing the error...

Actual density measurements are carried out using this:
http://aceglass.com/page.php?page=5415

mmm, some nice expensive glass to play with.... Honestly a SG bottle is a pain to use, some come calibrated other need calibration.

FireLion3 - 8-7-2014 at 10:42

I think the syringes may help some. The needles are very thin, probably not able to hold more than half a militer a water in the actual needle, and I assume the actual well of the syringe is accurately marked. They use these for medical purposes so I don't think a 5-10% difference is acceptable.

I needed these needles anyways. For doing reactions on a very small scale it has always been difficult for me to accurately add to solution exactly 50ml of a liquid, or exactly 5ml, etc. Even with super small beakers, it would be hard to add small quantities of liquids.