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Author: Subject: Is this right? Tap water in a chemical reaction?
antimon
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[*] posted on 20-9-2015 at 13:12
Is this right? Tap water in a chemical reaction?


Hi, i downloaded a pdf thats called 'Kings chemistry something' by a guy called Jared Ledgard.
In it on page 41 he describes a electrochemical reaction, making Chloroform from rubbing alcohol, Potassium Dichromate, pickling salt, H2SO4, and tap water.

Can this really be correct? I would have thought that all the chemicals thats added in the water coming out of our tap would mess up the reaction.
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aga
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[*] posted on 20-9-2015 at 13:17


The contaminants in your tap water could help or hinder the reaction - no idea which.

Distilled water is generally used simply so you know what is in the reaction mixture.

Given that the Haloform reaction works fine, it would seem a waste of sulphuric acid and potassium dichromate to me.

Do you have a reference to this pdf you downloaded ?

If not, please put any unreferenced questions in the Beginnings topic, where they belong.




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Texium
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[*] posted on 20-9-2015 at 13:31


Or even better, post it to the Short Questions Thread in miscellaneous instead.
Really it would depend on the tap water that you have, and on the context of how the pdf wants you to use it.




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[*] posted on 20-9-2015 at 13:32


Here's a link to the book the OP is talking about. http://catbull.com/alamut/Bibliothek/Kings_Chemistry_Surviva...

To answer your question, the amount of dissolved salts in tap water is quite low. Seeing as you distill the chloroform after removing it from the cell, there is no chance of contamination due to using tap water. Typically, tap water contains mainly a few salts, and metal ions will be plated out early in the electrolysis and any chloride contamination will not interfere with the reaction, seeing as you are already adding sodium chloride.

aga, the potassium dichromate is only present in catalytic amounts, it's not being used to oxidize the isopropyl alcohol to acetone.




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aga
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[*] posted on 20-9-2015 at 14:13


Thanks gdflp.

Without knowing anything about the Process i was mostly lost in space.

The bleach + acetone route still seems so much simpler.




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[*] posted on 20-9-2015 at 14:42


Quote: Originally posted by aga  

The bleach + acetone route still seems so much simpler.

I agree, unless the OP can't buy bleach.




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Dan Vizine
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[*] posted on 22-9-2015 at 08:03


Tap water has an undeservedly bad reputation for unsuitability for reaction use. I've run 90% of reactions, extractions, washings with tap water and it has no detectable ill effects.

There are reactions where it matters what grade the water is. For diazonium salt reactions, or a sol-gel polymerization, or a final recrystallization of a product, etc. I'd use deionized water. Our lab never had distilled water, and we made experimental drugs for NCI & Walter Reed.

Only once, when Monsanto wanted a pile of N-methylphosphono acetic acid purified (PALA to them, Round-up to you after they add an amine to make a salt) did we actually purchase water, HPLC grade, no less. They wanted kilos multiply recrystallized from this pure water for toxicology purposes. It was my first and last time using round-bottom flasks of 50 L and larger.





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[*] posted on 22-9-2015 at 08:47


Returning to the question of using tap water in reaction you need to consider what you are planning to do and will the components of the water cause a problem. The main "problem" components are Ca and Mg since they often form insoluble precipitates with many inorganic and organic acids (eg soap scum in hard water areas). Where I live the water is exceedingly soft and the main problem components are chloride and sulphate probably derived from sea spray carried inland by the prevailing winds but these are generally only a problem if I am using silver and barium solutions when they cause the solutions to become cloudy. Interestingly I have found that much "de-ionised" water has too high a chloride ion content to be used with silver nitrate and I have to resort to distilling water for this purpose. In the OP specific situation I can't see any problem using tap water unless you live in a very hard water area when you might get a ppt of calcium sulphate forming, though this should not be a big problem on an amateur scale.
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