bogmonkey
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Procuring ionic compounds using metathesis reactions
My knowledge of metathesis reactions is limited but if I'm not mistaken new salts can be formed from two soluble salts if the new salt happens to be
insoluble. Thats about all I know. Are there many useful non OTC salts which can be made this way from easy to find OTC salts such as NaCl,
NaHCO[SUB]3[/SUB], MgSO[SUB]4[/SUB]. I know about the solubility rules so really I'm being a lazy bastard and asking if anyone knows off hand of
useful salts that can be procured this way.
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hissingnoise
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| Quote: | | I know about the solubility rules so really I'm being a lazy bastard and asking if anyone knows off hand of useful salts that can be procured this
way. |
Why wait for answers from other lazy bastards when you can google the subject yourself. . .
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bogmonkey
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I have googled but didn't find specific information on the matter.
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hissingnoise
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If you can find this in your local library you're sorted. . .
http://www.wiley-vch.de/publish/en/books/bySubjectCH00/ISBN3...
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Polverone
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Download a copy of the CRC Handbook of Chemistry and Physics or Lange's Handbook of Chemistry as a starting point. Both books have fairly large tables
of solubility data for inorganic compounds that should give you a good starting point. Even more data can be found in the solubility compilations of
e.g Atherton Seidell and Arthur Comey.
For example, calcium chloride and sodium potassium tartrate are both relatively soluble in water. But calcium tartrate is much less soluble. When you
mix a solution of sodium potassium tartrate (easily prepared from potassium hydrogen tartrate, 'cream of tartar' and sodium carbonate) with a solution
of calcium chloride, beautiful needles of calcium tartrate soon crystallize out. I do not remember off-hand whether these needles are a hydrate or
not. You could design an experiment to determine how much (if any) water of hydration the precipitate contains if you want more discovery experience,
or just look it up if not.
You will also discover qualitative differences between different types of precipitation reactions. For example, by analogy with the experiment above
you may think that you can precipitate calcium sulfate by mixing solutions of calcium chloride and ammonium sulfate. You can, actually, but instead of
nice visible crystals you will get a very fine precipitate that is hard to filter and behaves like sludge if the starting solutions were concentrated.
In all of your attempted metathesis reactions you can also get comfortable working stoichiometry problems (if you aren't already) by determining how
many grams of each compound you should start with for exact balance. In case of more soluble metathesis products you may want to use an excess of one
starting compound or the other in order to force greater precipitation by the common ion effect.
PGP Key and corresponding e-mail address
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turd
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The main problem with your question is that OTC is a very fuzzy notion depending on your location and also contacts. For me red phosphorus is OTC, for
others it may not be so. Usefulness is of course in the eye of the beholder - only you can know what is useful for you. And your premise of salts
having to be insoluble is wrong. For example carbonates and ammonium ions can be driven away by acids and bases, respectively. So you might want to
think about a more precise question.
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ScienceSquirrel
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You could buy 500g of magnesium oxide from eBay.
From that you could prepare and crystallise magnesium chloride, magnesium sulphate and magnesium nitrate using OTC acids.
A solution of magnesium chloride reacts with magnesium oxide to form a hard porcelain like solid that was once used as a temporary dental filling.
I have made it in the past and as described it is incredibly tough but it is attacked by water and dilute acids.
http://en.wikipedia.org/wiki/Sorel_cement
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Xenoid
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Possible metathesis or "double dissolution" reactions are too numerous to list individually.
A good starting point would be to copy the solubility tables from Wikipedia;
http://en.wikipedia.org/wiki/Solubility_table
From these you will be able to see what is feasible and what is not.
A common metathesis reaction is the addition of KCl to solutions of NaClO3 or NaClO4 to obtain the corresponding K salts which are MUCH less soluble.
KNO3 was traditionally made from the metathesis reaction of NaNO3 (Chile Saltpetre) and KCl. It is now commonly made from a similar reaction with
synthetic NH4NO3.
Many reactions require that you work within certain temperature and concentration ranges to achieve maximum returns. I have used the all of the above
reactions many times, along with reactions for other corresponding chlorates, perchlorates and nitrates.
For example, Mn(NO3)2 and Co(NO3)2 and other "exotic" nitrates can be made from the corresponding sulphates and the readily available fertiliser
Ca(NO3)2. As pointed out by "Polverone", unless you have good vacuum or pressure filtering these can only be done at low concentrations.
You should also practice crystallising individual chemicals, slowly and quickly, for example to get a feel for the subject. Often, with concentrated
salt solutions it is possible to cool down to -10 or -20 oC. in the freezer to achieve maximum yield from a single crystallisation.
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entropy51
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Quote: Originally posted by ScienceSquirrel  | You could buy 500g of magnesium oxide from eBay.
From that you could prepare and crystallise magnesium chloride, magnesium sulphate and magnesium nitrate using OTC acids. |
I have used MgSO4 (Epsom salts) and Na2CO3 (washing soda) to make MgCO3 (actually a basic carbonate) and Na2SO4 by metathesis.
MgCO3 can then be reacted with acids per ScienceSquirrel. Merck says MgCO3 is converted to the oxide above 700 C.
CuSO4 (root killer from hardware store) solution reacts with steel wool to give nice flakes of Cu metal and a solution of ferrous sulfate.
CuSO4 + NaOH gives a dark blue precipitate of Cu(OH)2 which when warmed gives CuO. CuO can be reacted with vinegar to give cupric acetate. There is
a thread here with more details.
[Edited on 9-1-2010 by entropy51]
[Edited on 9-1-2010 by entropy51]
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ScienceSquirrel
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Fine steel wool can be used with drain cleaner type sulphuric acid to make iron II sulphate.
The wool is about 95% pure iron and the drain cleaner acid is not pure but filtration of the reaction mixture and a first crystallisation will produce
brilliant pale green crystals.
Combination with ammonium sulphate from your local garden centre will produce Mohr's salt.
This will recrystallise nicely from distilled water to produce a very pure and stable source of iron II ions.
Reaction with sulphuric acid, hydrogen peroxide and ammonium sulphate will produce ferric alum.
There are three interesting compounds to make from OTC materials.
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ScienceSquirrel
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If you can obtain some potassium dichromate you can make chrome alum aka potassium chromium sulphate.
There are recipes on the Internet for reacting potassium dichromate, sulphuric acid and any standard source of ethanol to make chrome alum.
I have done it with mordant grade potassium dichromate, bog cleaner acid and purple methylated spirit.
Temperature control is important but if you get it right the bright orange of the dichromate will change to a deep green solution. You will smell
acetaldehyde and later acetic acid and on cooling the solution brilliant purple crystals will form.
Recrystallisation from water will produce a really lovely crystal if you use a seed.
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ScienceSquirrel
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Reaction of aluminium metal as foil, scrap from drink cans or powder with potassium hydroxide solution will produce an aluminate solution and copious
amounts of hydrogen gas.
Reaction with sulphuric acid will produce potash alum.
Filtration and a first crystallisation will make nice crystals, a second crystallisation will make something that you can be proud of if you have the
technique.
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Nicodem
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Before anybody goes to the library, please note that the referred book is about olefin metathesis, which has nothing to do with the metatheses
reactions of which the original poster asked about.
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