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basically i need help with my chem extended hw.
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JosieAnneAllison
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Joined: 30/05/2010 - 11:32
Posts: 2
basically i need help with my chem extended hw.
JosieAnneAllison
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Joined: 30/05/2010 - 11:32
Posts: 2
basically i need help with my chem extended hw.

Okay so im really new to this website so how it works i dont know. and chemistry is not one of my strong subjects. so if you need help with history, music or english lit and english lang, i can help you in return for this favour.

anyways...

im having alot of trouble understanding the whole cathode anode and the equations that come with it.
i think the easist thing to do is to type out the question for you guys and maybe someone can help
me understand it. (btw the numbers not in bold are supposed to be small, index like numbers)

b) Aqueous copper(II)sulphate solution can be electrolysed using carbon electrodes. The ions present in the solution are as follows.
Cu2+ (aq) SO42 (aq) H+ (aq) OH (aq)

i) Write an ionic equation for the reaction at the negative electrode.(cathode)

ii) A colourless gas was given off at the positive electrode(anode) and the solution changes from blue to colourless. Explain thses observations.

i understand the whole Anode is positive and Cathode is negative, i just dont understand what we use this for and how to work out questions like this. With the whole ionic equations business i ask my teacher but she can't give me a simple explanation an easy way to look at it i suppose.

Thanks :)

chemistrysubjec...
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Joined: 10/06/2007 - 22:31
Posts: 347

Welcome!

The best way to use this is, I think, to look at the help pages to see if your problem has already been dealt with but questions like this are always welcome.

At the anode (attracting negative ions), the rule is "Get a halogen if one is available, otherwise get oxygen".

At the cathode (attracting positive ions) the rule is "Get the least reactive substance released".

So for copper sulfate solution:
(Sorry about the lack of subscripts etc)

There are two positive ions that will be attracted to the cathode: Cu2+ and H+. Copper is less reactive than hydrogen and so it gets produced as a pinky-brown coating on the electrode. H+ ions stay in solution.

Cu2+ + 2e- ---> Cu

There are two negative ions that will be attracted to the anode: SO42- and OH-. No halogen is available and so oxygen is released.SO42- ions stay in solution.

4OH- ---> O2 + 2H2O + 4e-

Hope this helps.