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?
(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.
(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.
(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.
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
(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?
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
(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
(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
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
(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