FireLion3
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Reagent Density issue, what factors can influence changes in density in a normal lab setting?
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]
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gdflp
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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?
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FireLion3
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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.
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Dr.Bob
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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.
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ScienceHideout
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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.
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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FireLion3
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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]
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ScienceHideout
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"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?
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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forgottenpassword
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What was the boiling point?
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Dr.Bob
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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.
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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.
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FireLion3
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| 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.
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]
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forgottenpassword
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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]
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ScienceHideout
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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 
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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FireLion3
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| 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.
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ScienceHideout
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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...
hey, if you are reading this, I can't U2U, but you are always welcome to send me an email!
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FireLion3
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| 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...
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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]
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PHILOU Zrealone
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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.
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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Dr.Bob
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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.
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Ascaridole
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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.
Ascaridole, the masked bandit of chemistry!
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HgDinis25
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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.
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Ascaridole
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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.
Ascaridole, the masked bandit of chemistry!
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FireLion3
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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.
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