Sciencemadness Discussion Board

Ammonium Persulphate production

evilgecko - 21-5-2005 at 17:39

Is there a DIY way to produce Ammonium Persulphate? I'm in need for some to etch copper board and would prefer this over ferric chloride. My local dse shop has stopped shipping this because it is a flammible hazard.

Axt - 21-5-2005 at 18:06

Why would you need your <i>local</i> dse to <i>ship</i> it to you? they never have sent it through the mail. Or are you saying they don't stock it anymore?
Quote:
Extract from Brauer

Ammonium Peroxydisulfate
(NH4)2S2O8
Prepared by anodic oxidation of a saturated (NH4)2SO4 solution:
2(NH4)2SO4 — 2 e = (NH4)2S2O8 + 2NH4+

A clay cup with a capacity of 130 to 150 ml. is placed in a 500ml. beaker of equal height. The cup is surrounded with a coil of lead tubing which serves both as a cathode and a cooling coil. The current lead is a copper wire soldered to the coil. A 0.05-cm.- thick Pt wire spiral anode, ignited prior to the run, is suspended in the middle of the cup. A mixture of equal weights of concentrated H2SO4 and H2O is used as the cathode liquid; the anode space is filled with an iron-free (NH4)2SO4 solution, saturated at 10°C [76.3 g. of (NH4)2SO4 in 100 g. of H2O ] . The cooling water flow is turned on, and the electrodes are connected through a rheostat and an ammeter to the 12-14 v. power supply. The current should be 2.5 amp. and the electrolyte temperature as low as possible. Slight evolution of O3 can be observed at the anode; simultaneously, an ozone odor is apparent. After 4-6 hours, white crystalline (NH4)2S2O8 separates in the clay cup.

The electrolysis is continued for some time and then the salt is suction-filtered on fritted glass. The remaining mother liquor is largely removed by pressing on clay. The product still contains a few percent of sulfate. To purify the compound, it is recrystallized (from as small an amount of water as possible) by dissolving at 40°C and then cooling an ice bath. The pure substance (negative test with BaCl2) is dried on clay and in the desiccator. After 10 hours of electrolysis the yield is 33 g. The anolyte liquid, saturated with (NH4)2S2O8, can be remixed with fresh (NH4)2SO4 and reelectrolyzed. The catholyte is gradually neutralized by NH4 and therefore must be tested with pH paper and replaced with fresh acid when necessary. After 3-4 hours, another 20-40 g. of (NH4)3S2O8 is obtained.

SYNONYM:
The older name is ammonium persulfate.

PROPERTIES:
Colorless, platelike or prismatic crystals; stable for months when pure and dry; decomposes in the presence of moisture, gradually evolving ozone-containing oxygen; strong oxidizing agent. Decomposes on heating, evolving O3 and forming (NH4)2S2O7.
d 1.98.
Solubility (0°C): 58.2 g.; (15.5°C) 74.8 g./l00 g. H2O. The solution decomposes slowly at room temperatures and rapidly at higher temperatures, evolving O3 and forming NH4HS04.
Monoclinic crystals, space group C5,2h.

REFERENCES:
E. Mviller, Elektrochemisches Praktikum [Electrochemical Practice]
, 7th Ed., Dresden-Leipzig, 1947, p. 212.
K. Elbs, J. prakt. Chem. [2] 48, 185 (1893).



Grab Brauer from the library: http://www.sciencemadness.org/library/index.html
Its by far the best electronic version getting around, though a page is missing.

[Edited on 22-5-2005 by Axt]

cyclonite4 - 21-5-2005 at 18:30

I think he means his local DSE store wont ship it in from their supplier anymore. I don't see why DSE is so worried about flammability, I would think it would be more likely for a butane gas can to cause an accident.

BTW, that brauer document looks like is suffering a few minor OCR'ing errors (I've yet to download it).

Axt - 21-5-2005 at 18:53

Quote:
Originally posted by cyclonite4
BTW, that brauer document looks like is suffering a few minor OCR'ing errors (I've yet to download it).


Only in the subscript, I just went through and fixed the obvious errors.

JohnWW - 21-5-2005 at 21:20

By DSE, do you mean Dick Smith Electronics? Cheapskates!

evilgecko - 22-5-2005 at 00:31

Yup Dickies it is...ok electrolysis with suplhuric acid and lead and Pt is way outta my league. Thanks for time you guys/girls took into writing replys though! It looks like I'll have to just use ferric chloride. Grrr DSE is so annoying they ban heaps of stupid toddler safe chemicals and then overprice anything thats left. Sometimes I think the world is too safe

cyclonite4 - 22-5-2005 at 04:35

The DSE I buy from, infact, all DSE's and other electronic suppliers I have gone to stock Ammonium Persulfate. What state are you in? Here in WA, I've yet to see a store without it.

I can understand why you dont want to use the ferric chloride etchant, you get much less use per bottle than with ammonium persulfate!
I think ferric chloride is more expensive too.

Have you tried other DSE's or other suppliers? If your in sydney or perth, look for altronics, they will definately have it.

evilgecko - 22-5-2005 at 20:58

lol thanks for the help but I live across the ditch in Kiwi land. There isn't a big market overhere with electrical components and so our DSE stores are filled with tvs, computers and phones. A tiny corner is spared for the nerdy side of things :-)

Twospoons - 23-5-2005 at 15:31

Go to Jaycar, instead! They sell ammonium persulphate, and don't sell ferric chloride. DSE is a waste of time for components, once was good (like 20 years ago) but now is full of spotty store clerks who don't know diddly about electronics.

Ammonium Persulphate

MadHatter - 24-5-2005 at 00:13

Evilgecko, is there any way to legally import it that you know of ? The shipping charges,
HAZMAT fees, and other bureaucratic bullshit may make it expensive but it's an alternative
if it's available to you.

Pommie - 24-5-2005 at 15:37

Unless you have a Jaycar nearby then it gets rather expensive. Ammonium Persulphate has to be shipped by road at a cost of AU$20. However, Jaycar do have 5 shops in N.Z.

Mike.

ADP - 30-5-2005 at 10:24

Speaking of, Ammonium Persulfate or Sodium Persulfate for that matter, does anyone know how the decomposition equation of these two compounds go?

I'm pretty sure they both release lots of SO3

Twospoons - 30-5-2005 at 14:25

No, absolutely not. I've used it and there is no smell or fizzing, just a few small bubbles which generally stay attached to the copper. The solution turns blue, like copper sulphate, which is probably what it is.

[Edited on 30-5-2005 by Twospoons]

chemoleo - 31-5-2005 at 12:43

(S2O8)2- + 2e <---> 2(SO4)2-

This is how it exerts it's oxidising power, by accepting electrons from a reductant. Exactly how it reacts i.e. with copper (during etching:

Na2(S2O8) + Cu ---> Cu(SO4) + Na2SO4


However, heat releases from sodium persulphate SO3 (try it - melt it, and get copious amounts of white fumes)

Na2S2O8 --> Na2SO5 (which decomposes further) + SO3

Pyridinium - 1-6-2005 at 07:30

I might be missing something obvious, but that Brauer passage doesn't mention how the anolyte and catholyte are put in electrical contact to complete the circuit (salt bridge? membrane?)... or does the cell rely on the different densities of solutions to keep them apart?

This has me thinking of a modified cell that doesn't use the lead tubing. Just trying to think of a way to cool it now...

ADP - 1-6-2005 at 09:31

Thanks for the info chemleo, I plan on experimenting with sodium persulfate and trying your method of using it to add to conc. H2SO4 to make H2S2O7. Sorry for the being off topic by the way.

Axt - 17-8-2006 at 10:27

Attaching - H. Marshall, "The Persulphates" J. Chem. Soc. (London) 59, 771-786 (1891)

Just 'cause I like these old articles dealing with the discovery of common chems.

[Edited on 17-8-2006 by Axt]

Attachment: the persulphates -j chem soc-59-771-778-(1891).pdf (551kB)
This file has been downloaded 1196 times

Axt - 17-8-2006 at 10:28

The second half.

Attachment: the persulphates -j chem soc-59-779-786-(1891).pdf (856kB)
This file has been downloaded 1158 times

woelen - 18-8-2006 at 01:10

Quote:
Na2S2O8 --> Na2SO5 (which decomposes further) + SO3

I wish this were true, but it isn't. Na2S2O8 is not useful as a source of SO3. I have tried this, and Taaie-Neuskoek (also a member here) has done a lot more research on this. It is all written in the thread on oleum and SO3.

No, Na2S2O8 simply gives O2 on heating and then it stops, you're left with Na2S2O7 and only with insane heat you get a pathetic yield of SO3.

YT2095 - 18-8-2006 at 02:57

mix a spatula of Na or K ClO3 to half a litre of HCl(aq) 30%.
the reaction is slow to start from a fresh soln unless you add a little copper chloride to it (not essential though).

I use this fro PCB etching, it works like a charm and will etch a huge amount of copper before it`s exhausted, when it is, keep a little of the exhausted soln and add that to a fresh batch.
as long as this soln is exposed to the air it will just carry on working :)
and HCl is much cheaper than other etchants.

12AX7 - 18-8-2006 at 14:21

ClO3 to ACID!?

I'm coughing already...

Tim

YT2095 - 19-8-2006 at 01:01

remarkably there`s little to no smell involved, or any bubbles formed during etching. probably due to the tiny amount used in order to kick-start the reaction, you could use Hydrogen Peroxide I beleive, after the reaction starts and the soln is a little used, it gets all its further oxygen from the air, if you did it in a sealed jar, the reaction would eventualy stall.
I was actualy given the mechanism that takes place, but have long since forgotten it, I just use it now :)
but I will try and look it up and see if I can find it again. either that or Woelen will be able to explain, as it was He that gave me the idea in the first place some time ago.

YT2095 - 19-8-2006 at 01:18

here:

--------------------------------------------------------------------------------------------------
Cu + CuCl4^{2-} -> Cu.CuCl4^{2-} -> 2CuCl2^{-}

The complex ion CuCl2(-) very easily is oxidized. Even oxygen from the air can easily oxidize this in the presence of acid:

4CuCl2^{-} + O2 + 4H^{+} + 8Cl^{-} --> 4CuCl4^{2-} + 2H2O

--------------------------------------------------------------------------------------------------

it`s rather elegant really, and saves a fortune (which is always good!).

woelen - 19-8-2006 at 11:44

Yes, indeed, this reaction is a very nice one. I also use it in electronics etching. You only need to start off the reaction with a little oxidizer (KClO3 is OK, but a few ml of bleach, or some 10% H2O2 is OK as well). So, you need no tons of oxidizer, just add a spatula or so to a few 100's of ml, or a small teaspoon to a liter.

In fact, a copper (II) solution in HCl is perfectly capable of oxidizing copper metal, and a deep brown mixed oxidation state copper (I)/copper(II)/chloro complex is formed. This in turn is very easily oxidized by oxygen from air, so the net reaction is oxidation of copper metal by oxygen from the air, and the only adidtional chemical, used up, is hydrochloric acid. For replenishment, you only need to add some HCl occasionally and the etching liquid should be allowed to keep in contact with air for some time, in order to reoxidize the copper (I) to copper (II).

One could regard this as a self-catalyzing reaction, the copper (II) (better: chloro complex of copper (II)) is a catalyst for oxidation of copper metal by oxygen. The mechanism for the reaction, already is perfectly explained by YT2095.