Terminology? (heated to reflux, washed, etc)

  • Thread starter mc2718
  • Start date
  • #1
2
0

Main Question or Discussion Point

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."
 

Answers and Replies

  • #2
1
0
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."
This is a very common procedure in organic lab.
1) heated to reflux, yes it is usually at a high temperature enough such that some components of the liquid will boil and vaporise, but since it is within a closed vessel, it will eventually condense back to be part of the solution, and this continuous process can help speed up reaction(in terms of activation energy)

2) usually leave it to cool for a while, then you wash with sodium carbonate in a separatory funnel, this is to remove all the acid unreacted. you would need to release the pressure inside the funnel after shaking for a while, CO2 buildup can be dangerous.

3) from that, you'd get an organic layer and an aqueous layer. You want the organic layer, that is your product. Get this separated from the aqueous layer and then add anhydrous MGSO4(drying agent).

4) Filter either with suction filtration or normal filtration.

5) usually people add in a minimum amount of very hot solvent to dissolve the filtered product. Then either cool naturally or cool in ice bath, scratching the flask waiting for crystals to form, do suction filtration to collect the crystals again. you can wash the remaining stuff with COLD solvent(very little bit).

6) This is your product, as pure as you could probably get in teaching lab. Do mp analysis, nmr, ir or whatever tests necessary.
 
  • #3
2
0
Many thanks for the quick response.

2) usually leave it to cool for a while, then you wash with sodium carbonate in a separatory funnel, this is to remove all the acid unreacted. you would need to release the pressure inside the funnel after shaking for a while, CO2 buildup can be dangerous.
I see, so technically this gives me Na+whateveritiscalled (phthal-something) salt + H2CO3 acid, the latter however dissolves easily since the CO2 concentration outside is negligible and I just get the water back. Neat.

By the way, why use the HCl afterwards?

3) from that, you'd get an organic layer and an aqueous layer. You want the organic layer, that is your product.
Does "washing" mean the whole procedure, including the removal of the water (at the bottom of the funnel) that was introduced when these two solutions (Na2CO3 and HCl) were added?


4) Filter either with suction filtration or normal filtration.
Many thanks for these helpful keywords.

5) usually people add in a minimum amount of very hot solvent to dissolve the filtered product. Then either cool naturally or cool in ice bath, scratching the flask waiting for crystals to form, do suction filtration to collect the crystals again. you can wash the remaining stuff with COLD solvent(very little bit).
Oh, so operationally this is nothing like growing those salt crystals on a thread....

---

By the way, is there a good website about the properties of the various chemical substances? I could not find the resulting N-phenyl-phthalimide on Wikipedia...
 

Related Threads on Terminology? (heated to reflux, washed, etc)

  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
13
Views
17K
Replies
10
Views
5K
  • Last Post
Replies
4
Views
22K
Replies
1
Views
2K
Replies
2
Views
2K
Replies
4
Views
2K
Replies
5
Views
3K
Replies
5
Views
1K
Replies
4
Views
789
Top