hodges
National Hazard
Posts: 525
Registered: 17-12-2003
Location: Midwest
Member Is Offline
|
|
Phosphoric Acid from Baking Powder?
I'm curious if it would be possible to make phosphoric acid, starting with baking powder.
Ingredients list from a can of baking powder: "Calcium Acid Phosphate, Bicarbonate of Soda, Cornstarch".
Presumably once you add water to this your final result (after release of CO2) will be a mixture of calcium and sodium phosphates (not sure which
specific phosphates or the percentages of each since I don't know the original concentrations). So the next step would be to somehow separate
the cornstarch. I believe it can dissolve in water? Perhaps the phosphates could then be precipitated out using magnesium salts since magnesium
phosphate is insoluable? Once you had magnesium phosphate you could add HCl to convert it to magnesium chloride (soluable) and phosphoric acid
(insoluable at low temperatures)?
Does this sound reasonable? Any better ideas?
|
|
|
Rosco Bodine
Banned
Posts: 6370
Registered: 29-9-2004
Member Is Offline
Mood: analytical
|
|
Phosphoric acid 85% is sold by the gallon at building supply and hardware stores . It is used as a rust remover / rust stabilizer treatment or bare
metal cleaner
before primer painting steel or iron . The syrupy liquid is a green color from a slight natural iron and chromium impurity in the technical grade
product which is made from phosphate rock by treatment with sulfuric acid .
If you check garden suppliers for "triple superphosphate" you will find a soluble calcium dihydrogen phosphate , Ca(H2PO4)2 which should
produce the same orthophosphoric acid and a precipitate of calcium sulfate , upon treatment with sulfuric acid . These would be more economical
sources than baking powder .
Trisodium Phosphate , TSP , is sold as a degreaser detergent powder for cleaning surfaces before painting , and is usually in the paint department of
building supply stores or else in with the deck cleaners and other specialty cleaning supplies .
|
|
|
hodges
National Hazard
Posts: 525
Registered: 17-12-2003
Location: Midwest
Member Is Offline
|
|
Rosco, thanks for the information on alternative sources. I was actually interested in doing this more for the challenge, especially if one could say
they got their phosphorous out of ordinary baking powder from the grocery store!
Here is how I ended up doing it. After reacting the baking powder with water, I added some HCl. This converts the phosphates to their mono-basic
form. For example, Ca3(PO3)2 is converted to CaH2PO3. I chose HCL instead of H2SO4 because H2SO4 might lead to the formation of insoluable CaSO4. I
let the solution settle, which allowed me to pour off the clear solution while leaving the cornstarch and other contaminents behind. I then added
NaOH to again produce Ca3(PO4)2, which is insoluable. I poured the liquid (complete with precipitate) into a 1 liter plastic bottle. I let the
precipitate settle, then added more water to wash the precipitate. I repeated this process about 8 times to get rid of the excess NaOH. I then dried
the resulting precipitate in the oven. Result was a white powder.
The white powder should be Ca3(PO3)2. To test this, I mixed the powder in about 2:1 ratio with pyro-grade Al. I heated a small amount (around 0.5g)
with a torch. It ignited, although not to vigorously, reacting about as fast as iron and sulfur do when heated together. Here is the reaction:
3Ca3(PO4)2 + 6Al --> 3Ca3P2 + 8Al2O3
After the reaction had cooled I added a drop of water and noticed the smell just like impure acetylene (which contains a bit of phosphine due to
impurities when made with calcium carbide).
For another reaction, I mixed in both aluminum powder and fine silica powder:
3Ca3(PO4)2 + 10Al + 4SiO2 --> 6P + 5Ca(AlO2)2 + 4 CaSiO3
This reaction required much more heating with a torch and was not self-sustaining (it glowed for a while but then went out before all the reactants
were consumed). The phosphorous produced burned with a flame similar to a candle flame as it was produced.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
