[mc2718]

Hi,

Could someone help me out regarding chemist lingo?

i) "were heated to reflux for one hour"

Does it mean that the stuff was heated, or even boiling, but with condensing the vapor back to the container (so that the solvent is not lost)?

ii) "the solution was then washed with 5% aqueous Na2CO3"

Does this simply mean that you pour in the Na2CO3 dissolved in water, and that is all, or is there something else done?

iii) "was allowed to stand over solid anhydrous Na2SO4 for 15 minutes"

Does this mean you just pour it over that Na2SO4 (powder, I guess), and wait?

iv) "after slowly cooling the solution, crystals were obtained, which after filtering and drying gave a melting point of 205°"

How do you filter CRYSTALS?? Also, is drying really what a layperson would think (i.e., let it dry over air, or like using the hair-dryer), or is it something different?

v) solubility units

If solubility is given as a number without any units (e.g., 0.03, or 6.3), does that mean simple molar ratio (stuff to solvent)?


Thanks for any help to elucidate these. I am trying to make sense of this experiment:

"Phthalic acid and aniline were heated to reflux for one hour. Upon cooling, the mixture was dissolved in ether and placed in a separatory funnel. The solution was then washed with 5% aqueous Na2CO3 followed by 5% aqueous HCl and allowed to stand over solid anhydrous Na2SO4 for 15 minutes. The ether was then evaporated and a solid product obtained.

The crude product was dissolved in an appropriate hot solvent and after slowly cooling the solution, crystals were obtained, which after filtering and drying gave a melting point of 205° to 207°C. The literature value for the melting point of the expected product is 208°C."

[sjb]

Hi,

Could someone help me out regarding chemist lingo?

i) "were heated to reflux for one hour"

Does it mean that the stuff was heated, or even boiling, but with condensing the vapor back to the container (so that the solvent is not lost)?

Yes, that's my understanding too, heated so that it boils but the solvent re-condensed into the reaction.

ii) "the solution was then washed with 5% aqueous Na2CO3"

Does this simply mean that you pour in the Na2CO3 dissolved in water, and that is all, or is there something else done?

In your case, you may have phthalic acid as unreacted starting material. You would add sodium carbonate to neutralise this, so that you can purify your crude material to an extent this way.

iii) "was allowed to stand over solid anhydrous Na2SO4 for 15 minutes"

Does this mean you just pour it over that Na2SO4 (powder, I guess), and wait?

Again, you can do that, but it probably implies drying the organic phase, so you may agitate the ether and see if you get a snowstorm style effect to ensure that it's dry.

iv) "after slowly cooling the solution, crystals were obtained, which after filtering and drying gave a melting point of 205°"

How do you filter CRYSTALS?? Also, is drying really what a layperson would think (i.e., let it dry over air, or like using the hair-dryer), or is it something different?

In a solution, you have a filtrate (like a solvent) and solid crystals, basically you're removing the solvent, somewhat like sand / water. You can dry in air, or under vacuo, under increased temperature, depends what you need to remove the solvent.

v) solubility units

If solubility is given as a number without any units (e.g., 0.03, or 6.3), does that mean simple molar ratio (stuff to solvent)?

Difficult to say, which is why units are always important.

Thanks for any help to elucidate these. I am trying to make sense of this experiment:

"Phthalic acid and aniline were heated to reflux for one hour. Upon cooling, the mixture was dissolved in ether and placed in a separatory funnel. The solution was then washed with 5% aqueous Na2CO3 followed by 5% aqueous HCl and allowed to stand over solid anhydrous Na2SO4 for 15 minutes. The ether was then evaporated and a solid product obtained.

The crude product was dissolved in an appropriate hot solvent and after slowly cooling the solution, crystals were obtained, which after filtering and drying gave a melting point of 205° to 207°C. The literature value for the melting point of the expected product is 208°C."

[mc2718]

Thank you for the quick response, this will obviously take more  than one round

In your case, you may have phthalic acid as unreacted starting material. You would add sodium carbonate to neutralise this, so that you can purify your crude material to an extent this way.

Alright, I see the strategy - but I still do not see clearly what is actually DONE. It really escapes me why it is called WASHING and not mixing, or simply adding... once they pour in the extra fluid, do they do something else, or nothing at all?

Again, you can do that, but it probably implies drying the organic phase, so you may agitate the ether and see if you get a snowstorm style effect to ensure that it's dry.

How can it be dry if it is soaked in ether . what do chemists mean by 'dry' then? Hmm... snowstorm??

[...] basically you're removing the solvent, somewhat like sand / water.

Oh, I see... so these are nothing like those big crystals you grow from ordinary table salt...

Difficult to say, which is why units are always important.

I am sure these are not *missing* units. The values I saw quoted have no units whatsoever. This would not surprise me - there are many examples in physics (e.g., refraction index, Abbe number, Mach number, Reynolds number, Knudsen number, etc). But chemists have like 10 different quantities for solubility on Wikipedia... I am sure there must be a reason but it is pretty confusing, to say the least.

[sjb]

Alright, I see the strategy - but I still do not see clearly what is actually DONE. It really escapes me why it is called WASHING and not mixing, or simply adding... once they pour in the extra fluid, do they do something else, or nothing at all?

Probably just jargon to an extent, yes, the two liquid phases are simply mixed together and possible agitated, be it in a separating funnel or Erlenmeyer.

How can it be dry if it is soaked in ether . what do chemists mean by 'dry' then? Hmm... snowstorm??

Dry in this case simply means water-free. As to the "snow-storm" effect, I mean like these toys, at e.g. http://www.worldcollectorsnet.com/magazine/issue43/iss43p6.html

Oh, I see... so these are nothing like those big crystals you grow from ordinary table salt...

They can be, if you're patient and / or lucky.

I am sure these are not *missing* units. The values I saw quoted have no units whatsoever. This would not surprise me - there are many examples in physics (e.g., refraction index, Abbe number, Mach number, Reynolds number, Knudsen number, etc). But chemists have like 10 different quantities for solubility on Wikipedia... I am sure there must be a reason but it is pretty confusing, to say the least.

I know what you mean, but the same quantity can have different dimensionless values. For instance taking 1 litre of ethanol and 1 litre of water at room temperature (ignoring the fact that they make a non-ideal mixture for the moment), this would be 50% v/v ethanol, but as ethanol is less dense than water, it's only about 44% w/w, or 24% mol/mol

Pure dimensionless numbers are, in my mind always calculated with consistent units, so a circle with radius 7 m has a circumference of ~ 44 m, making pi ~ 22/7. Now, if we had measured the radius as 700 cm, this would make pi ~ 22/700 (not simplfied to aid discussion) m / cm, still dimensionless to an extent, as cm and m both measure length.

[Borek]

there are many examples in physics (e.g., refraction index, Abbe number, Mach number, Reynolds number, Knudsen number, etc). But chemists have like 10 different quantities for solubility on Wikipedia...

You are comparing apples (unitless numbers) with oranges (numbers with units). Ideal gas constant (while used in chemistry) is basically a physical constant:

http://en.wikipedia.org/wiki/Ideal_gas_constant

see table on the right

Or think about all possible units used for pressure - PSI, Pascal, atm, mmHg and so on.

Solubility is just a concentration of saturated solution - and concentration can be expressed in as many interchangeable ways as you want. But it should have units, no doubts about it. Sometimes - when units are used consistently throughout the book/paper - they are explained in appendix.

One of the common ways of expressing solubility is grams of substance per 100 g of solvent.

[mc2718]

Thank you guys, I think I finally understand more or less what is being done. Just one last question,
how can it be 'water free', if they pour in beforehand basically WATER with a little bit of Na2CO3 and HCl in it?

One of the common ways of expressing solubility is grams of substance per 100 g of solvent.

And thanks for this eye-opener, as well - so even a factor of 100 could be lurking in there.

[sjb]

Thank you guys, I think I finally understand more or less what is being done. Just one last question,
how can it be 'water free', if they pour in beforehand basically WATER with a little bit of Na2CO3 and HCl in it?

Water and ether are not that miscible, so what you will have is a biphasic mixture, ether on the top, water on the bottom. You will take the majority of the water away via the sep funnel. What's left is ether, your amide, and a small amount of water that is soluble in the ether layer. It's the latter water that is removed by drying with the sodium sulfate.

Perhaps you need to have a look at things like Procter, Harwood or Zubrick (three separate books, I can dig ISBNs out if you want), to understand procedures?

[mc2718]

You will take the majority of the water away via the sep funnel.

Oh, I see. Why does the original description of the process (bottom of post #1) not say ANYTHING about how / whether that sep funnel is actually used? There is no statement like "we carefully drain the water at the bottom of the funnel" or whatever...

Or is that what "washing" meant, in contrast to adding/mixing??

Perhaps you need to have a look at things like Procter, Harwood or Zubrick (three separate books, I can dig ISBNs out if you want), to understand procedures?

Sounds like a good idea, thanks for the reference.

[sjb]

I suppose typically a "wash" is used in this way, and that it implies you discard the solvent that you wash with, as opposed to "extract with", which implies you keep that phase.

[PolymerKnowHow]

I would also add that "washing" also typically implies multiple, small additions of sodium carbonate solution.
That and the washing with sodium carbonate and hydrochloric do not occur at the same time, but rather in sequence.
Google separatory funnel extractions for some basic instructions.

Question: Why are you interested in such a procedure? The best way to learn these techniques and terminology is through a supervised environment such as a organic chemistry class/lab.

[Mr.rose]

Just to hijack this thread,

So if Somthing states

"This product is soluble in chloroform (50 mg/ml). It is
also soluble in a number of oils, including ethyl oleate.
It is practically insoluble in water,
soluble 1 in 6 of ethanol, 1 in 4 of acetone, 1 in 20 of
ethyl oleate, and 1 in 30 of propylene glycol."

What does the unitless values "1 in 6", "1 in 4" etc stand for? gram/gram, mole/mole? etc