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Thread: Reactions with salt water

  1. #1 Reactions with salt water 
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    today after school, i tried to make pure sodium by getting a large battery and attaching rolled up aluminum foil to the two terminals and putting the ends of the foil in a container of salt water. of course, this didn't create pure sodium at all. instead, according to wikipedia, it created hydrogen gas, chlorine gas, sodium hydroxide, and as i discovered after the submerged part of the aluminum connected to the positive terminal dissolved, Na3AlO3. after the reaction began to stop, i removed the aluminum. what is left now is a gray liquid beneath a clear liquid which im allowing to evaporate to see what happens.

    i wanted to do the experiment again without using a metal that would react with the solution, so i attached galvanized nails to the ends of the aluminum foil rolls and put those in the salt water. however, this turned the salt water very dark with a dark green-brown film on the top that looks like algae and what looks like a gray liquid on the bottom. its hard to tell because its in a translucent plastic container. also, the nail attached to the positive terminal seems to be dissolving. the tip seems to be more dull and the submerged part has become darker, although something may just be depositing on the nail.

    so does anyone know what is happening in the second experiment? im not sure what kind of metal is beneath the zinc on the nails. i would guess that all galvanized nails have the same metal beneath the zinc, but if not i can find the box and check.


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  3. #2  
    Forum Professor leohopkins's Avatar
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    What is taking place is oxidisation.

    The reason why we galvanise steel or iron with zinc is because zinc oxidises quicker than the steel or iron.

    Try and remember too that salt water is a solution and NOT a compound. So, if you get rid of the water by either electrolysis or evaporation, you will be left with sodium chloride; still.

    Basically what you are doing in your experiment is releasing the hydrogen atoms. The free oxygen atoms left over are reacting with the metals.
    The sodium chloride remains unchanged.

    If you do want to conduct the experiment again without using a metal that will react with the solution then try using gold.


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    Moderator Moderator AlexP's Avatar
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    for your um... i can't remember what that part is called, that you used nails for, you need to use, as leo said, gold, or i think platinum works, or graphite. however, to obtain pure sodium from electrolysis, you need molten NaCl, not an aqueous solution of it... and besides, pure sodium isn't something you want around anyway: it explodes on contact with water. and chlorine gas is very toxic, and i think if you breathe enough in it basically burns your lungs out... so yeah, have fun electrolyzing that NaCl!
    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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  5. #4  
    Forum Freshman Keith's Avatar
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    Quote Originally Posted by Chemboy
    for your um... i can't remember what that part is called, that you used nails for
    Cathode/anode maybe? :-D
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  6. #5  
    Moderator Moderator AlexP's Avatar
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    Quote Originally Posted by Keith
    Quote Originally Posted by Chemboy
    for your um... i can't remember what that part is called, that you used nails for
    Cathode/anode maybe? :-D
    yeah, that. i was tired. would they collectively be called electrodes? that's what i was thinking of really, but i wasn't sure, so i didn't want to say it.
    "There is a kind of lazy pleasure in useless and out-of-the-way erudition." -Jorge Luis Borges
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  7. #6  
    Forum Freshman Keith's Avatar
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    Yes, collectively they would be called electrodes.
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  8. #7  
    Forum Bachelors Degree The P-manator's Avatar
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    As far as I can tell, the experiment to get sodium turned into good ol' elecrolysis, with the salt in the water acting as an electrolyte.
    Pierre

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  9. #8  
    Forum Sophomore Kabooom's Avatar
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    Electrolysis doesn't work to get pure sodium because the sodium when liberated from the chlorine then reacts with H2O and combines with the oxygen (I think). I know for a fact that sodium somehow reacts with water though, so it doesn't work in electrolysis.

    unitednuclear.com is a good place to get things like pure sodium...
    WHAT?!
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  10. #9  
    Forum Bachelors Degree The P-manator's Avatar
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    I think that's what's been said all along. Electrolysis produces hydrogen and oxygen and the sodium chloride merely acts as an electrolyte, speeding up the process and enabling lower amp usage.
    Pierre

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  11. #10 Sodium Metal 
    Forum Freshman Dantak's Avatar
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    No one has addressed that it is nearly impossible to obtain sodium metal in a home lab. Sodium has one more electron than it needs to obtain a full octet and will do what ever it takes to get rid of that electron. You will certainly not systhesize it in water. None of the alkali metals can exist in water because they react violently with water. That's why they are stored in oil.
    Here is a brief summary of the isolation of sodium.
    Sodium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative sodium ion Na+.

    Sodium is present as salt (sodium chloride, NaCl) in huge quantities in underground deposits (salt mines) and seawater and other natural waters. It is easily recovered as a solid by drying.

    Sodium chloride has a high melting point (> 800°C) meaning that it sould be expensive to melt it in order to carry out the electrolysis. However a mixture of NaCl (40%) and calcium chloride, CaCl2 (60%) melts at about 580°C and so much less energy and so expense is required for the electrolysis.

    cathode: Na+(l) + e- → Na (l)

    anode: Cl-(l) → 1/2Cl2 (g) + e-

    The electrolysis is carried out as a melt in a "Downs cell". In practice, the electrolysis process produces calcium metal as well but this is solidified in a collection pipe and returned back to the melt.
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