ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: onlyfknhuman on November 03, 2008, 09:05:43 pm
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From the TSSM practice exam
English scientist, Sir Humphry Davy, first isolated potassium in 1807 by electrolysis of
molten potassium hydroxide.
a.
i. Write balanced half equations for the reactions that will occur at the anode and the
cathode in this cell.
anode __________________________________________________________
cathode __________________________________________________________
The Answer are
anode 4OH-(l) -> O2(g) + 2H2O(g) + 4e-
cathode K+(l) + e- -> K(l)
since its molten, were do they pull out water from? From Sir Humphry Davy's ass?
Much appreciated
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the anode reaction is producing water, not consuming it.
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and it's a gas when it's produced, so it escapes into the atmosphere [or is captured] and does not contribute to subsequent reaction
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ah crap, i see
wait, so why isnt the anode 2OH- +H2 -> 2H20[l] + 2e-
instead of 4OH-(l) -> O2(g) + 2H2O(g) + 4e-
is it because the water produced is a liquid? where as the answer is a gas.
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no
it's because in the prior, you require H2 as a reactant, which you do not have.
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How do you know H2 is required? >_< sorry for being so stupid :S
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because in the first one its 2OH- + H2
but you dont have any H2 so you know that cant be the reaction
therefore it has to be 4OH- -> O2 etc.
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omfg im blind !!
thankss everyone