Rhodium (Chief Bee)
10-31-02 02:13
No 374739
      Purification of formaldehyde  Bookmark   

An old bottle of formaldehyde of unknown concentration, with 1 cm of precipitate at the bottom, can this be distilled or something to get 37% formaldehyde solution?
 
 
 
 
    SPISSHAK
(Hive Bee)
10-31-02 02:16
No 374742
      That sounds like floculation  Bookmark   

Or polymerization, heat it and see if it dissolves.
I'm not sure exactly under what conditions formaldehyde floculates but It's a guess.
 
 
 
 
    Rhodium
(Chief Bee)
10-31-02 02:21
No 374744
      It will probably redissolve with heating, but the ...  Bookmark   

It will probably redissolve with heating, but the concentration is unknown, I'd like to make sure I have a 37% solution.

The conditions under which my bottle flocculated was by prolonged storage at 5-10C.
 
 
 
 
    SPISSHAK
(Hive Bee)
10-31-02 02:27
No 374747
      I'm not sure how you would test for concentration  Bookmark   

Other than specific gravity, or by seperating the two, I think a certain percentage of methanol is added to formalin solutions to keep it from doing this so it probably is spontaneous.
If you heat it to much you'd either A: distill off the methanol
B: the methanol would condense on the formaldehyde and produce Methylal.
During this process the paraformaldehyde would depolymerize by reaction with water.
Depending on what extent you heat it to.
 
 
 
 
    lugh
(Moderator)
10-31-02 03:01
No 374756
      Paraformaldehyde  Bookmark   

Paraformaldehyde is formed when formaldehyde solution is evaporated, it's probably what's on the bottom smile When paraformaldehyde is heated with a large quantity of water, it's reconverted into formaldehyde smile
 
 
 
 
    Rhodium
(Chief Bee)
10-31-02 03:10
No 374760
      How can I determine the concentration?  Bookmark   

How can I determine the concentration? Or perhaps I should rather heat a known weight of paraformaldehyde with water instead?
 
 
 
 
    lugh
(Moderator)
10-31-02 03:48
No 374773
      Concentration  Bookmark   

The specific gravity of formaldehyde is 1.075-1.1081 smile You could calculate the percentage of a solution prepared from heating paraformaldehyde in a large quantity of water to that to determine your concentration smile The aqueous solution boils at 98C, the boiling point of the gas is -21C smile
 
 
 
 
    b159510
(Professional Student)
10-31-02 03:51
No 374775
      ~,~  Bookmark   

How can I determine the concentration

iodimetric titration, after 5 minutes add hydrochloric acid and back titrate with na-thiosulfate.

or like you said, mix up a new batch, which would probably be easier if you don't have a standardized triiodide solution already made.


You don't fool me, Oilman
 
 
 
 
    b159510
(Professional Student)
10-31-02 04:27
No 374787
      trioxymethylene  Bookmark   

Paraformaldehyde is formed when formaldehyde solution is evaporated...

I've dissolved paraformaldehyde in water, but never evaporated the solution. Isn't that how trioxymethylene is formed? (aka metaformaldehyde, 1,3,5-trioxane)
You don't fool me, Oilman
 
 
 
 
    lugh
(Moderator)
10-31-02 04:49
No 374794
      Triformol  Bookmark   

Yes, as posted in Post 209590 (lugh: "Re: Acquiring Acetaldehyde OTC", Chemicals & Equipment) smile Triformol is the trimer, paraformaldehyde is the hexamer, which melts at 171C smile
 
 
 
 
    b159510
(Professional Student)
10-31-02 04:58
No 374797
      my mistake  Bookmark   

The titration I mentioned should still work for an aqueous solution of formaldehyde, even though that isn't the species that actually exists.
(What is that called, methanediol?)
You don't fool me, Oilman