Do you guys know any techniques to balance complex Redox reactions?

[BrownEMS]

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I hate how balancing equations is an art. It takes far too long to balance anything.

I had difficulty balancing:

Au + NaCN + O2 + H2O ---> Na[Au(CN)2]+ NaOH

Can anyone show me their way to quickly balance this.

Bear in mind, balancing this equation is part of a question with secondary complexity (balancing the equation to find how many moles of Au after Titration).

It took me too long to balance this.

 

[basophilic]

To come up with a nicer way to solve this will come through intuition built through lot of practice. But IMO, doing the old half-reactions way is probably the most reliable, which is what you want in the middle of a nerve-racking test.

Having said that, here's how I'd do it if I wasn't allowed to do it the traditional way:
1. Look at the oxidation changes b/w reactants and products - I see that Au goes from 0 to +1; each O in O2 gets reduced from 0 to -2 (so actually O2 goes from 0 to -4).
2. Since Au provides the electrons, I'll need 4 Au to get 4 electrons to reduce a single O2; after this it's all downhill, since now you just have to balance both sides.
3. Put 4s before Au and the complex product; 8 in front of NaCN (since now there are 8 CNs in products); 4 in front NaOH to get 8 Na's in products; and finally a 2 in front of H2O to equalize the Os and Hs on both sides