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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: kettles on March 11, 2012, 11:49:19 pm

Title: Identifying redox reaction
Post by: kettles on March 11, 2012, 11:49:19 pm
Hey guys, how would you know if something is a redox reaction by just looking at the equation? What are the keys which distinguishes this equation from a standard acid/base or a precipitation.

example


Which of the following reactions would be classes as a redox reaction?

a) 6CO2(g)+6H2O(l)==>C6H12O6(aq)+6O2(g)
b)CaC2(s)+2H2O(l)==>Ca(OH)2(aq)+C2H2(g)
c)H2SO4(aq)+Ca(HCO3)2(s)==>CaSO4(aq)+2H2O(l)
d)FeS(s)+2HCl(aq)=>FeCl2(aq)+H2S(g)
Title: Re: Identifying redox reaction
Post by: destain on March 11, 2012, 11:52:18 pm
I think you would check to see if there is a change in the oxidation numbers?
Correct me if im wrong...
Title: Re: Identifying redox reaction
Post by: Nobby on March 12, 2012, 12:00:30 am
I think you can also just skim over the reactants are products for some reactions; i.e. if you have O2 or Cl2 or some other homonuclear product it must be redox
Title: Re: Identifying redox reaction
Post by: Shenz0r on March 12, 2012, 10:58:55 am
Looking at oxidation numbers will definitely tell you if it's a redox reaction
Title: Re: Identifying redox reaction
Post by: kettles on March 12, 2012, 11:44:45 am
shen can yo udo this question so i can see your work process.
Title: Re: Identifying redox reaction
Post by: Shenz0r on March 12, 2012, 03:08:07 pm
Quote from: kettles on March 11, 2012, 11:49:19 pm
Which of the following reactions would be classes as a redox reaction?

a) 6CO2(g)+6H2O(l)==>C6H12O6(aq)+6O2(g)
b)CaC2(s)+2H2O(l)==>Ca(OH)2(aq)+C2H2(g)
c)H2SO4(aq)+Ca(HCO3)2(s)==>CaSO4(aq)+2H2O(l)
d)FeS(s)+2HCl(aq)=>FeCl2(aq)+H2S(g)

You have to "test" all the reactions to see if they're a redox. I'm assuming you know the rules for oxidation numbers. I'll show you how to test for oxidation in the first equation and then you should be able to do the rest yourself.

For a):
    +4  -2            +1 -2                         0
6 C     O2       + 6H2O -> C6H12O6 + 6O2

O.N for Carbon in glucose = 6x+12(1) + 6(-2) = 0
x = 0

Carbon's O.N has decreased from +4 to 0 and therefore it has been reduced, oxygen's O.N has increased from -2 to 0, indicating that this is a redox reaction.