blogfast25
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Ammonium Alum: simple synthesis from OTC materials
Although originally referring to the potassium aluminium double sulphate (KAl(SO4)2.12H2O), once one of the most important sources of water soluble Al
salts and precursor to the name ‘alumin(i)um’, alums are now considered a class of chemical compounds of the general structure MM’(SO4)2.12H2O
where M is a monovalent cation (e.g. K+, Na+,… , NH4, even Tl+) and M’ a trivalent one (e.g. Al3+, Fe3+, Cr3+ and even Mn3+).
This post is a simple recipe for making about 0.5 mol (about 226 g) of NH4Al(SO4)2.12H2O, ammonium aluminium alum or ammonium alum for short, from OTC
materials with high yield and a nice looking highly water soluble Al compound to show for one’s effort.
Chemicals needed:
13.5 g of fairly clean aluminium (I use opening tabs of Al pop cans).
55 ml of H2SO4 95 % (I use a toilet or drains unblocker).
Some 1 M H2SO4 - prepared from above.
33 g of (NH4)2SO4, ammonium sulphate. I use once-recrystallised garden grade, beige in colour.
Water - deionised, distilled or very soft.
Procedure:
Add aluminium to a roomy Pyrex container and add 100 ml of water to it. Add the 55 ml of concentrated sulphuric acid slowly while stirring. Reaction
will start according to Al(s) +3/2 H2SO4(aq) === > ½ Al2(SO4)3 (aq) + 3/2 H2(g). Add another 100 ml of water and put the covered container on an
electrical hot plate (avoid open flame: HYDROGEN!) Simmer lightly until nearly all of the metal is dissolved. Top up volume of solvent with 1 M H2SO4
if it drops below 200 ml. Dissolution will take 1 - 2 hours, depending conditions.
Below: aluminium reacting with H2SO4 in conditions described.
The last bits of metal can take a long time to dissolve and I do as follows. Add 33 g of ammonium sulphate dissolved in about 100 ml of hot water to
the aluminium sulphate solution and keep hot. That should give you about 300 ml of total volume. Hot filter the ammonium alum solution quickly with a
coffee filter (small amounts of alum may crystallise on the filter) and receive the filtrate in a sturdy but flexible container (HDPE or PP - it can
be hard to remove the formed crystals from a glass container without damaging it).
Add some seed crystals; allow cooling to RT, then put on ice bath or in a refrigerator overnight. Separate crystals from mother liquor and determine
yield. My slightly moist crystals amounted to about 96 % theoretical yield.
Recrystallise by adding 1 part of water to 2 parts of product, heat gently to about 100 C while stirring until all crystals have dissolved. Add some
seed crystals; allow cooling to RT, then put on ice bath or in a refrigerator overnight. The recrystallised product tends to show larger, more
regular, snow white crystals and yield of recrystallisation is nearly 100 %.
Below: just over 200 g of ammonium alum prepared with this procedure.
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m1tanker78
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Simple, clean, OTC. Thanks for sharing the synth. BTW, what color is your plumbing grade H2SO4? Mine is a very nasty dark brown so I often hesitate to
use it.
Tank
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blogfast25
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Quote: Originally posted by m1tanker78  | Simple, clean, OTC. Thanks for sharing the synth. BTW, what color is your plumbing grade H2SO4? Mine is a very nasty dark brown so I often hesitate to
use it.
Tank |
Mine is red. Mankind's tendency to put dyes and flagrances into just about anything never ceases to amaze me... Or vitamins in hair shampoo, what's
that all about? 
I've found though that for most purposes the red dye doesn't cause any problems and is probably distilled off during use.
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#maverick#
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very nice easy synth and nice yield, and m1 the first brand i had was dark brown, rooto professional drain opener is totally clear
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m1tanker78
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Marketing and the plecebo effect?
Mav, I'll keep my eyes open for Rooto brand drain cleaner. I think mine's branded "clear shot" or something similar.
Tank
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blogfast25
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Yes, marketing of course: 'here comes the science bit" (NOT!). Today the new symbol of the double helix is what you want to put on every jar of 'face
paint for women' to flog your product...
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Mr. Wizard
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@blogfast25
13.5 g of fairly clean aluminium (I use opening tabs of Al pop cans).
What is the alloy they use for aluminum cans? I know the alloy for the tops is different from the main can. It usually has more magnesium in it. Other
elements from memory include manganese, copper, and silicon
Your results look very good, but I was wondering about Magnesium and other alloy components in the mix. Thanks for sharing.
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blogfast25
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| Quote: Originally posted by Mr. Wizard | @blogfast25
13.5 g of fairly clean aluminium (I use opening tabs of Al pop cans).
What is the alloy they use for aluminum cans? I know the alloy for the tops is different from the main can. It usually has more magnesium in it. Other
elements from memory include manganese, copper, and silicon
Your results look very good, but I was wondering about Magnesium and other alloy components in the mix. Thanks for sharing. |
To be honest, I haven't got the foggiest idea. But for this purpose trace elements like Mg, Mn and Cu should stay in the mother liquor because they're
highly soluble and present only small in amounts. Any Si will have been filtered off...
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m1tanker78
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| Quote: Originally posted by blogfast25 | | Yes, marketing of course: 'here comes the science bit" (NOT!). Today the new symbol of the double helix is what you want to put on every jar of 'face
paint for women' to flog your product... |
"Well, if it has the DNA thingies on the bottle, it MUST be good! Aloe vera is sooooo yesterday." (satisfied customer testimony) 
+++++++++++++++++++
Impurities from the alloy shouldn't be an issue (I can't speak for Mn). This synth is on the to-do list for the near future. It's a perfect excuse to
break in (hopefully not break) my new boro kettle.
Tank
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blogfast25
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| Quote: Originally posted by m1tanker78 |
Impurities from the alloy shouldn't be an issue (I can't speak for Mn). This synth is on the to-do list for the near future. It's a perfect excuse to
break in (hopefully not break) my new boro kettle.
Tank |
Tut tut: no should need an excuse to break in a new boropot. But you do need one to break it!
Meanwhile I've been running a few more runs but with ferric ammonium alum (NH4Fe(SO4)2.12H2O). Really hard to get good yields. Saturday I lost a 1
mole size batch (turned to Fe2O3, basically), today by the looks of it I'm getting good Q but less than 50 % yield. Bugger! 
[Edited on 31-7-2011 by blogfast25]
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jamit
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Root professional drain opening is not clear but is technical grade with a tint of yellow/brown with a very very very slight pink or red. Rooto
sulfuric is still the very best OTC sulfuric acid and usable for most home chemistry.
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