electrolysis with Salt water....

[steakyfask]

im learning all about chemisrty at the mo, so i decided to put a bit of theory to praticle and i have a few questions..

 

i know that NaCl dissolves in water to give [Na]+ ions and [Cl]- ions

when i put a current through the solution what started off as a green/yellow gas (which is now slowing turning browny/orangish) collects at the anode, am i right in thinking this is chlorine gass being given off?

 

The only change i can see at the cathode is a change in colour around the wire, when i started it was silver now it seems to be a copper like colour, what is this? i would asume that this is the Na ions but i know its not as Na reacts violentlywith water ...

 

 

how would i go about getting the Na from this soloution and how can i make HCl?

 

 

thanks

Edited January 20, 2010 by steakyfask

[hermanntrude]

You cannot get sodium like this:

 

http://www.scienceforums.net/forum/showthread.php?t=40177

 

There are ways to get sodium but they're all extremely dangerous, and of course sodium itself is pretty nasty too.

 

As for HCl, again there are various ways, but this is not the way.

 

However you are correct in saying you've made Cl2, chlorine gas. Be careful breathing around that stuff it can be quite harmful.

 

One method for making HCl (which i don't recommend trying) is to fill a small testtube with H2 and Cl2 gases, and then expose them to a bright burst of sunlight. An explosion occurs and HCl gas is created. Obviously there are better ways but generally they don't start with chlorine gas.

[the guy]

the cathode should produce hydrogen gas, leaving hydroxide ions, and sodium, which reacts with the hydroxide ions to give sodium hyrdoxide solution, this then reacts with the chlorine to give sodium hypochlorite. if you want to get chlorine and sodium hydroxide you need to keep them separate by using permeable diaphragm (unglazed pottery would do like a plant pot) so they do not react. you could then use the hydrogen and the chlorine given off to produce hydrogen chloride, perhaps using a tubes with a flashback arrestor installed for safety (a cigarette filter would do) and bringing them together and lighting them, they would burn together and you could collect the hydrogen chloride produced (i don't know how affective this would be i've never tried it)

 

To get sodium you have to do electrolysis of molten sodium chloride (which melts at about 800 degrees celcius) or molten sodium hydroxide (which melts at a lower temperature but its a dangerous chemical itself) and then you have to make sure the sodium doesn't come into contact with air or water because it is so reactive, so you'd be better off not attempting this.

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the colouration could be the chemicals reacting with the cathode, what material did you use?

[Fuzzwood]

The hydroxide ions don't react with the sodium ions. They are simply both dissolved in the solution, leaving you with a sodium hydroxide solution.

[the guy]

well its the same thing really

[dttom]

The cathode should leave hydrogen gas, and the color change you mentioned I guess it is due to metal oxide reduction by the gas.

[steakyfask]

hmmm yes maybe i should stay away from trying to make HCl or Na.

 

i used asda table salt mixed in tap water, in a plastic container. im not sure what material the wires were but they were just standard red and black wires i got from a build your own morse code set.

 

would i have got different results if i had deided to use two graphite pencils for the anode and cathode?

 

 

when i left the current running through the wire there were three coloured clowdy substances seperated at the bottom of my container (one was blue, one was yellow/brown and the other was green) i left the solution for a while to come back and find the wire from the anode (i think) had been eaten away by a chemical reaction... i left the solution over night (without the current) and now all that remains is a clowdy light blue substance sitting at the bottom.... any ideas what this is?

[Fuzzwood]

Those are copper ions which precipitated with the formed hydroxide into basic copper salts.

[steakyfask]

wherre do the Cu ions come from ? all i have is table salt and water...

[Fuzzwood]

And your wires.

[the guy]

copper wires

[hermanntrude]

The cathode should leave hydrogen gas, and the color change you mentioned I guess it is due to metal oxide reduction by the gas.

 

the colour change is due to chlorine gas. Oxygen requires a fairly hefty overpotential, as does chlorine, so you usually get a mixture of both gases depending on the voltage and concentration of the salt. I know that if you use very concentrated salt and a 9V battery you get a LOT of chlorine (so much so i wouldn't do that indoors)

[rogerxd45]

you should use carbon electrodes. that way they wont react with your solution. when you use wires you get copper mixed in which will sometimes react with the chlorine and give copper chloride thats a greenish color in the solution

[theoriginal169]

to have hcl your method is true i think you hace cl at anode h2 at chatode so u can mix them am i wrong?

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hmmm yes maybe i should stay away from trying to make HCl or Na.

 

i used asda table salt mixed in tap water, in a plastic container. im not sure what material the wires were but they were just standard red and black wires i got from a build your own morse code set.

 

would i have got different results if i had deided to use two graphite pencils for the anode and cathode?

 

 

when i left the current running through the wire there were three coloured clowdy substances seperated at the bottom of my container (one was blue, one was yellow/brown and the other was green) i left the solution for a while to come back and find the wire from the anode (i think) had been eaten away by a chemical reaction... i left the solution over night (without the current) and now all that remains is a clowdy light blue substance sitting at the bottom.... any ideas what this is?

 

and dont afraid from chemicals they are harmless if u now how to act.

[Farrah Day]

you should use carbon electrodes. that way they wont react with your solution. when you use wires you get copper mixed in which will sometimes react with the chlorine and give copper chloride thats a greenish color in the solution

 

Stainless Steel electrodes are relatively inert in this environment, and they're easily available in form of everyday kitchen implements, (knives, spoons, etc).

 

Due to it's availability and low cost, SS is actually the preferred material in most electrolyser set ups commonly found on the internet. Rods and plates are relatively very easy to come by.

[UC]

Stainless Steel electrodes are relatively inert in this environment, and they're easily available in form of everyday kitchen implements, (knives, spoons, etc).

 

Due to it's availability and low cost, SS is actually the preferred material in most electrolyser set ups commonly found on the internet. Rods and plates are relatively very easy to come by.

 

Actually no, with chlorine around, you will damage stainless steel. SS is fine when using sodium hydroxide or sulfuric acid electrolyte, but nothing with halide ions present.

 

I have dissolved samples of stainless steel with chlorine water for example

[rogerxd45]

well carbon electrodes are easy to get from the large 6v CARBON ZINC batteries, not the alkaline ones. ususally if it doesnt say what type it is its usually the cheaper carbon zinc type.

 

you get 4 electrodes with wires attached that are about 4" long and the cost of the battery at walmart was only $2

 

thats 0.50 each

[Cena]

Water that is saline contains significant amounts referred to as "concentrations" of dissolved salts. In this case, the concentration is the amount by weight of salt in water, as expressed in "parts per million" (ppm). If water has a concentration of 10,000 ppm of dissolved salts, then one percent 10,000 divided by 1,000,000 of the weight of the water comes from dissolved salts.The salinity concentration level used by United States Geological Survey classifies saline water in three categories. Slightly saline water contains around 1,000 to 3,000 ppm.undermount sink

Edited November 19, 2010 by Cena