Sciencemadness Discussion Board

The density of my Trisodium Phosphate from a supplier is way off... possible reasons?

Lillica - 12-2-2017 at 00:23

I purchased some Trisodium Phosphate from a chemical supplier and didn't think much of it. I used it in a reaction and the reaction did not turn out how I expected it to, there was practically no reaction/conversation at all. I figured I had just messed something up in some other way and didn't think much else of it.

Today when I was weighing out some of the Trisodium Phosphate again, I noticed the density of the powder was something like 0.90g/cm3, which seems really strange because the anhydrous form should be 2.5g/cm3, whereas the dodecahydrate is 1.62. My way of measuring the density is just by pouring the powder in a beaker and checking the lines. I know these lines have a 10%+- error.... but that would not explain such a drastic difference in expected density. It's also unlikely that this is the Dibasic or Monobasic salt either because both of those still have a much higher density. I do note that the product is easily soluble in water like an inorganic would be.


Did I get sold the wrong product? I wanted to ask here before I call up the supplier and suggest they sold me the wrong thing. Is there explainable reason the density could be so off? The solid isn't in a "fluffy" form or anything like that.





[Edited on 12-2-2017 by Lillica]

JJay - 12-2-2017 at 00:55

There is a widely available trisodium phosphate cleaning product on the market that is actually only about 50% TSP. I don't know if this is what you have, but many of the common industrial chemical supply companies wouldn't know the difference unless you were looking for something specific.

Do you have any information on the product's grade or a CoA? The supplier should be able to provide you with a CoA if this is intended to be a lab grade chemical. If not, you should be able to at least find an SDS.

Generally speaking, chemists don't usually measure solids by volume since it is hard to do it accurately in a consistent and repeatable manner, especially with small amounts.

[Edited on 12-2-2017 by JJay]

Lillica - 12-2-2017 at 01:18

I bought my product from a Chemistry/Lab Supplier, so yes it is a lab grade product... it wasn't a random off the shelf product. My guess is that they grabbed it from the wrong container by mistake or something. I don't have the exact CoA on hand but I had asked and he said it is at least 97-98%, technical grade I believe.

I do understand the slight differences in volume, but I had filled a 250ml beaker to the 250ml line, and even pushed the powder down some, and it still said there was only 235g of product. When I purchased it, I had purchased about 450g, and it filled up about half of a 1-liter plastic jar. I knew the product was supposed to be dense, but I didn't notice the low density at the time because I was assuming that I was getting the correct product. It wasn't even a thought in my head.


I just want to make sure there's not some weird occurrence taking place here. There's nothing I can think of that would cause such a dramatic difference in density. If the correct density that 450g should have filled up about 173ml of the jar, not almost half of it.


[Edited on 12-2-2017 by Lillica]

JJay - 12-2-2017 at 01:20

Did you check the specific gravity of a solution?

Lillica - 12-2-2017 at 01:29

No I haven't yet.

I am reluctant to further handle this material since I have no idea what it is. I have never seen a pure compound have this much of a difference in density from known density. I've seen instances where the material was very very fluffy with small particle size, but even in those cases, the density is still relatively close, not 3x less. Given that this material isn't even fluffy, but almost in a crystalline/powder form with decent sized chunks, I believe something is definitely amiss.




[Edited on 12-2-2017 by Lillica]

JJay - 12-2-2017 at 01:38

I don't really know what to tell you, but if you call up your chemical supplier complaining that a cup of dry TSP didn't weigh out right, they are going to have a lot of questions for you.

Lillica - 12-2-2017 at 01:47

What sort of questions do you anticipate I'll be asked? I was just planning to tell him that the density is way off and nowhere near where it should be. I've had Trisodium Phosphate in the past, both the hydrate and the anhydrous and the density has never been like this.

The chemical supply store is small shop run by a single person and I'm in there almost every week. Me and the owner have a good relationship, though, he is getting a little old and he has been forgetful on more than one occasion. What I'm guessing happened is he filled my jar from the wrong container or something, since he did it in a hurry.

I just wanted to post and get some second opinions here before I call him. I'm just curious if anyone here will have a possible explanation for why the density is so off.

laserlisa - 12-2-2017 at 01:53

You cant really measure density of a solid like that can you? Unless you grow a uniform crystal of it and then measure its volume and weight because there will be a lot of air between the particles giving you a much lower density than it should be.

unionised - 12-2-2017 at 01:55

https://en.wikipedia.org/wiki/Bulk_density

Lillica - 12-2-2017 at 02:01

I did give thought to bulk density, but I don't think it is the culprit here. Reason being is that this powder is already fairly compressed as it is. I can take some out, compress it, and it doesn't compress that much more. I've seen the effect of bulk density vs real density on many hundreds of different solid reagents, but have never seen this drastic of a density difference.

I made a point about this above when I mentioned past experiences dealing with very fluffy / small particle size solids.


[Edited on 12-2-2017 by Lillica]

Sulaiman - 12-2-2017 at 02:13

The density of a powder is always less than the solid form of the same stuff, due to air spaces/packing efficiency.
OR
you may have

According to Wikipedia a 1% solution of TSP has a pH of 12
(I assume 1% by weight, e.g. 1g TSP per 100g solution)
so you could make a 1% TSP solution and 'measure' its pH with pH papers (cheap, useful, must have)
Dilute 1ml of the 1% TCP solution with 9ml water for pH11 etc.
OR
do a titration against an acid.
the acid could be vinegar, calibrated/titrated against sodium carbonate (sodium bicarbonate in a hot oven for an hour)
whilst the oven is in use, you should put your TSP in to dehydrate to the anhydrous form, to ensure a known hydration level.
This should be done for the above option also.
A burette is ideal for titrations, graduated pipettes or measuring cylinders will give a close enough result for a test, you could even count drops,
e.g. how many drops of acid to neutralise 10, 100 or (extreme patience required) 1000 drops of TSP
OR
you could re-crystalise your TSP from water to purify it,
the Wikipedia solubility table pages https://en.wikipedia.org/wiki/Solubility_table
show that TSP is a good candidate for re-crystalisation as the solubility at 20C is 12.1 g/100ml and at 100C it is 77 g/100ml
e.g. dissolve 77g TSP in 100ml boiling water, when the liquid cools to 20C you should recover 77 - 12.1 = 64.9 g of TSP if anhydrous,
since the crystals will be TSP.12H2O you should get about 150g
OR
since you are on good terms with your supplier, ask him how you could test it ?

[Edited on 12-2-2017 by Sulaiman]

[Edited on 12-2-2017 by Sulaiman]

Lillica - 12-2-2017 at 02:22

Sulaiman, that is what unionised was suggesting above with respect to bulk density. The powdered form will always be less dense than the crystal form... but we are talking about a 3x difference in density here for a powder that is already fairly compressed. When dealing with bulk density, under such circumstances, usually the difference between that powders bulk density and its actual density is somewhere in the range of a 10-20% error. More so if the powder is very fluffy, but this is not the case here. My powder is already fairly compressed. 3x density difference is a lot.

I unfortunately don't have any PH papers with me. My PH meter is currently is being borrowed by a friend at the moment, as I didn't use it very often to begin with.

The TSP should already be anhydrous, as I inquired about this before, with it being a lab grade chemical.

I will start a recrystalization in a few hours and see what the result is.

JJay - 12-2-2017 at 02:33

Quote: Originally posted by Lillica  
When dealing with bulk density, under such circumstances, usually the difference between that powders bulk density and its actual density is somewhere in the range of a 10-20% error.


According to background information in this patent, what you're stating here simply isn't the case: https://www.google.com/patents/US3607021

Sulaiman - 12-2-2017 at 02:41

according to the patent that you pointed to, third paragraph:

"In conventional methods of preparation wherein a routine neutralization of the mother liquor is carried out, mother liquor is dried and the range of density of the product will be from 0.65 to 0.85 gram per milliliter"

Tsjerk - 12-2-2017 at 02:48

Maybe explain what reaction you tried to preform? I guess what you have is TSP and nothing else. The density given is the density of one single crystal, a powder can easily diver a factor three.

Lillica - 12-2-2017 at 02:54

Quote: Originally posted by JJay  
Quote: Originally posted by Lillica  
When dealing with bulk density, under such circumstances, usually the difference between that powders bulk density and its actual density is somewhere in the range of a 10-20% error.


According to background information in this patent, what you're stating here simply isn't the case: https://www.google.com/patents/US3607021



That link isn't really debunking what I said above. That's actually exactly what I was looking for. It would seem based on that patent paper that Trisodium Phosphate does exhibit abnormal behavior with its density.

What I was stating about the 10-20% variation in bulk density is just based on my experience working as a chemical handler and repackager. I've handled somewhere around 200 different reagents, and for the majority of solids the bulk density is relatively predictable with the known documented density.
Quote: Originally posted by Tsjerk  
Maybe explain what reaction you tried to preform? I guess what you have is TSP and nothing else. The density given is the density of one single crystal, a powder can easily diver a factor three.


I would agree with you if this solid wasn't mostly crystalline already. The only time I have ever seen a 3x density difference in powders is when they are very fine and fluffy, which this isn't. That is why I've thought it is unusual.


[Edited on 12-2-2017 by Lillica]

JJay - 12-2-2017 at 03:06

Quote: Originally posted by Lillica  


...based on my experience working as a chemical handler and repackager. I've handled somewhere around 200 different reagents....



I see. Well, that's interesting. I know I am not the only one on this board who buys chemicals....





[Edited on 12-2-2017 by JJay]

Tsjerk - 12-2-2017 at 03:13

OK, but can you describe what reaction was not working for you?