elem school project

[steve]

MgSO₄ + Cu + H₂O
4 T epsom salts in 2 cup container
used 2 ea Cu electrodes
added water to fill to 2 cups
applied 16 VDC across electrodes
please complete equation and balance it if possible
TIA
steve

[Zedekiah]

Hello steve,

I admit that my weak point is electrochemistry, so all I can do here is take a stab at it.

The experimentation process here is going to be key to identifying products of this reaction.

My guess is that there is going to be substantial corrosion of the anode in the form of cupric oxide formation.

I'd be willing to bet with this much voltage, that magnesium metal is going to be formed at the cathode and oxygen gas at the anode. If you don't notice a silvery metal forming at the cathode and instead you for a gas, you're making hydrogen.

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2(Mg²+  + 2e-    --->    Mg)
2H2O   --->        O2 + 4H+ + 4e-

2Mg²+    +  2H2O       --->     2Mg    +   O2  +  4H+

So basically, you're making sulfuric acid and magnesium.

Try it out and see what you get, that will help you identify the products.

[sharan]

hey from wut think you shud be making a copper hydroxide Cu(OH)₂ as you have no chances of making CuSO₄ and sulfuric acid and Mg metal as:

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MgSO4 + Cu + 2 H2O = Cu(OH)2 + H2SO4 + Mg

hope that helps,

[steve]

Thanks Zedekiah;
Well...I should have told you more. Both electrodes were Cu sheets about 1.5 inches square. After about 3 hrs after power-up the neg electrode was completely gone and the solution seemed blue-ish. There were 2 types of crystals on the bottom...some blue-ish and some white. During the process there was lots of bubbling from the positive electrode moving towards the neg. electrode. No litmus paper here. We weren't trying to do anything or make anything, just see what happens... I got the idea from my 10-yr old when he came home from school after his science class...intro to chemestry.
Thanks for help ans some furthur ideas...
steve
*****

[steve]

Thanks Sharon!
That was exactly what I was looking for...right or wrong (grin).
steve
******

[Zedekiah]

I love a good mystery

If the solution was blue, then copper ions must be in the solution. One half reaction must then include copper being oxidized. Bubbling at the cathode can only mean one thing : hydrogen gas. The actual reaction is going to be more complex than what we're going to come up with, but this conforms with your latest descriptions :

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Cu    →    Cu²⁺  + 2e⁻

2H2O → O2 + 4H⁺ + 4e⁻

3( 2H2O + 2e⁻ → H2 + 2OH⁻)

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Something like :

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Cu + 8H2O  →  2OH⁻ +  3H2  + O2  + Cu²⁺

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We now know that magnesium is probably a spectator. Sulfate is most likely spectating as well (it almost has to; you can't oxidize it and reducing it takes a lot of effort). The blue stuff on the bottom was probably copper hydroxide and the white stuff may have been magnesium hydroxide; they're both insoluble.

Edit : Not much happens with a 9v battery.