ATAR Notes: Forum
VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: dusty_girl1144 on September 18, 2008, 01:57:16 am
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ok to be honest i dont COMPLETELY understand the concept of electrolysis and how to use the god damn electrochemical series
galvanic cells are fine.
ok so the question that i wanna know is....
1. where do i use the 2 water equation
2 determine cathode and anode PRODUCTS, overall reaction and required voltage for [ POTASSIUM - SULPHATE] , [SODIUM HYDROXIDE] HYDROCHLORIC ACID ] (why did u choose to do this)
dont make this reply MASSIVE LONG AND THEORETICAL. simple would be nice so i can grip the concept pretty quickly :)
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1. Write down everything present in your solution
Eg you have K2SO4, NaOH, HCl all dissolved in water, therefore you have K+, SO4-, Na+, OH-, H+, Cl-, H2O present
2. Get your electrochemical series and circle each of those ions/molecules listed
3. Find the highest one circled on the left hand side (of course with all reactants circled), eg in O2 (g) + 2 H2O (l) + 4 e- -> 4 OH- (aq) you can't choose that because you need O2 as well as H2O
In your example this is 2 H+ (aq) + 2 e- -> H2 (g)
4. Find the lowest one circled on the right hand side
In your example this is O2 (g) + 2 H2O (l) + 4 e- -> 4 OH- (aq)
5. Check to make sure that the one on the right is higher in the series than the one on the left, otherwise it wouldn't be an electrolytic reaction.
6. Write equation out:
4OH- + 4H+ -> 2H2 + O2 + 2H2O
Voltage required is the difference between the two, ie 0.40 - 0.0 = 0.40 for this one
Cathode will have the reaction going from left -> right (gaining electrons), ie so H2 is being formed at cathode
Anode will have the reaction going from right -> left (losing electrons), so O2 and H20 are being formed at anode
Tell me if it makes sense or you need more explaining etc :)
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You're not required to write the actual species in their half-equation form in order of increasing reductant strength in the actual exam right? I'd rage so hard if you did.
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No, I'm just saying circle it on the electrochem series so you don't miss any =)