[darthryan1]

Hello,

I am trying to produce sodium acetate for the popular supersaturated recrystallization demo. I have added an equimolar amount of bicarb to white distilled vinegar and boiled that away, but all I get is a light brown, clunky powder, mixed with a bit of white throughout.

I have found that the product is a little less brown if I boil it a bit more gently, but I have also tried evaporating the solution instead of boiling, only to still receive the same mysterious brown powder. The brown powder is soluble in water, forming a dirty chocolate brown solution. I have also tried neutralizing with NaOH instead, only to receive the same result. Thinking impurities, I have tried two store bought brands of vinegar with no difference in result.

This reaction is well-known and should be pretty straightforward. Where am I going wrong?

[woelen]

These must be some impurity. This reaction really is simple and yields a white product, not some dark brown crap.

Vinegar usually is not only acetic acid in water, but it can also contain salt, sugars, and spices. But if it is colorless, then it should not contain too much of those impurities.

What is the source of your sodium bicarbonate? Did you buy the pure chemical, or did you buy baking powder from a supermarket? The latter is impure sodium bicarbonate and contains a lot of other organic stuff. If you have pure sodium bicarbonate, then the powder must be snow-white (and not off-white with a light yellowish tint) and when it is added to water, it must dissolve without any turbidity. Also, when added to acid, it must fizz a lot and dissolve without leaving any turbidity.

[beheada]

I recall reading:

Sodium Acetate can be prepared by adding an equimolar amount of sodium hydroxide to glacial acetic acid.

Sodium Hydroxide is available for biodiesel/soap production and glacial acetic acid is available as a photography chemical. In doing this with only pure compounds, you avoid the nuisance of using "grocery" chemicals, which often (like woelen said) have extra things in them.

Hope that helps?

.rayfe-

[pantone159]

I'd guess the impurities are in the vinegar, not the bicarbonate.  I have done this with grocery store NaHCO3 and (diluted) glacial acetic acid, and got nice white/colorless crystals.

[constant thinker]

Try making sure the bottle says distilled vinegar. That is bound to have fewer impurities. I'm actually not really sure what companies mean by sticking the distilled word on the bottle. I've assumed it to mean that it's glacial acetic acid diluted with deionized water, but I think that's a little hopeful.

If you can try to purchase glacial acetic acid (caution it hurts to get on you, a lot) and NaOH from a chemical supplier.

[mike]

Maybe try not boiling the solution to dryness. Instead make the supersaturated solution and precipitate out the sodium acetate.