Equalizing equations by oxidation numbers?

[thedarkshade]

I know this might look silly to some people in here (as there are lots of more important subjects to discuss) what I'm gonna ask, but I really need to figure out how these things work! We've been dealing with some complicated (for me:doh: ) equations lately (like H2O2+KMnO4+H2SO4--> ...), and I just can't figure out how to equalize them using oxidation numbers (as our professor said it is easy to equalize by using oxidation number when the equations are tricky).

 

Could anyone please use any examples of equalizing equations using oxidation numbers and explain them?!

I really got to learn them!!!

 

Ooooh, come guys, this thing is really important to me! Any hint would be just fine!

Pleasee!

 

for example this equation.

 

5H2O2 + 2KMnO4 + 3H2SO4--> K2SO4 + 2MnSO4 +O2 + 8H2O

 

I know that both sides now are equal, but I just want to know to know how can we do this by using oxidation numbers!

 

I'm very interested to know. Any clue??

[ChemSiddiqui]

I know this might look silly to some people in here (as there are lots of more important subjects to discuss) what I'm gonna ask, but I really need to figure out how these things work! We've been dealing with some complicated (for me:doh: ) equations lately (like H2O2+KMnO4+H2SO4--> ...), and I just can't figure out how to equalize them using oxidation numbers (as our professor said it is easy to equalize by using oxidation number when the equations are tricky).

 

Could anyone please use any examples of equalizing equations using oxidation numbers and explain them?!

I really got to learn them!!!

 

Ooooh, come guys, this thing is really important to me! Any hint would be just fine!

Pleasee!

 

for example this equation.

 

5H2O2 + 2KMnO4 + 3H2SO4--> K2SO4 + 2MnSO4 +O2 + 8H2O

 

I know that both sides now are equal, but I just want to know to know how can we do this by using oxidation numbers!

 

I'm very interested to know. Any clue??

 

I think he must have asked you to try to balance it simply but I am not sure how to do it using oxidation state. I think if the oxidation number is balanced from each side of very individual atoms then it [equation] is balanced.

 

Sorry to be of no further assistance!

[thedarkshade]

I took a two-month chemistry course and now I'm fine with oxidation numbers and equalizing equations. Although my relations with my current chemistry teacher are suffering a downfall due to his desire to get all the credits and some horrible things he says (imagine what would be your teacher told you that lightnings have an average voltage of 380V! It drove me completely mad!).

 

Thanks for reply anyway!

 

Cheers!

[Mr.Chockuls]

Redox, it is'nt?

[ChemSiddiqui]

I took a two-month chemistry course and now I'm fine with oxidation numbers and equalizing equations. Although my relations with my current chemistry teacher are suffering a downfall due to his desire to get all the credits and some horrible things he says (imagine what would be your teacher told you that lightnings have an average voltage of 380V! It drove me completely mad!).

 

Thanks for reply anyway!

 

Cheers!

 

 

O, alright then, Sorry I was a little dumb there not to realise that you posted it ages ago . But I happy for you for taking the course and finally cracking the problem:-) !

[cosmic-chris]

Am i right in saying that oxidisation is the taking away of electrons and redox is the adding of electrons in a chemical equation?

 

And that its to do with the outer shells of the elements?

[YT2095]

Reduction is the "Adding" of electrons.

Redox is looking at Both sides: REDuction OXidation.

[thedarkshade]

I'd go with YT here.

 

[ce]2KBr + Cl2 -> 2KCl + Br2[/ce] This is a redox process because the oxidation numbers of the elements taking part in the reaction have changed. [ce]Cl2[/ce] from the oxidation number 0 has gone to -1, so it has received an electron and has been reduced itself, but it has played an oxidation role. So elements that are reduced, they itself serve as oxidation tools. And the other way around too.

 

[ce]Br2[/ce] from the oxidation state -1 has gone to 0, so it has lost an electron (the one that chlorine got). In this case [ce]Br2[/ce] has been oxidated and itself has served as reduction tool!

 

Just like YT said, oxidation is the addition of electrons. Chlorine has been an oxidation tool in this case since it has given Br an electron and has been reduced itself.

 

Thanks for everything guys!

 

Cheers,

Shade

[cosmic-chris]

Thanks fore the insight i didn,t know if i had rememberd it right.

 

thanks guys.

[ChemSiddiqui]

Thanks fore the insight i didn,t know if i had rememberd it right.

 

thanks guys.

 

And further if hydrogen is added to a molecule then it is also reduced and opposite is true for oxidation. Also if the oxidation number for an atom is increased then its oxidised and if decreased then reduced.

 

Oxidising agent are there which oxidise substance but themselves being reduced while reducing agents reduce substance but get oxidise themselves!

[foodchain]

And further if hydrogen is added to a molecule then it is also reduced and opposite is true for oxidation. Also if the oxidation number for an atom is increased then its oxidised and if decreased then reduced.

 

 

I prefer Electronegativity but also I had a hard time with basic chem until I started to read a physics perspective on it really. They just tried to pass concepts on without explaining anything which for me is a real pain educationally speaking as a student. Its the same with this, why do we need to classify such as such? Is it truly fundamental or just usable definition really? I like chem a lot also, so don’t get confused if you don’t see my posts in many chemistry threads as I don’t trust my advice that well on the issue:D

[YT2095]

electronegativity is EVERYTHING to do with it, but it`s not a workable "unit" as such, so Oxidation state or Valency (when I was taught) is used, less so Valency now though.

 

effectively the "magic" number is 8, and you need a Periodic table (or a good memory) to know what each element is in way of electron count.

 

you simply look at what group it`s in and there`s your answer, although it gets a bit more interesting when you get to the Middle groups as they CAN swing either way (esp Group 4).

 

they can be the Oxidiser Or reducer

 

think Calcium Carbide or Carbon dioxide for instance, the Carbon plays 2 different roles here.

 

but lets use an example given in the OP and look at H2SO4.

 

H=1 (but we have 2 so that 1x2=2)

S= 6

O=6 (but we have 4 of them so it`s really 6x4=24)

 

so lets add them add them up as Ions SO4 (the sulphate ion) adds up to 24+ 6 and that`s 30

 

so how many 8`s go into 30? well we know it goes into 32 4 times, so it`s 3 remainder 2, so we can scrap the 3 as that obeys the rules and we don`t need it anymore, we want the Remainder!

 

we also know the SO4 is the Oxidiser (it`s way over on the left on the periodic table) so it`s Overall charge is -2 (remember the remainder?).

 

Happily we have those pair of Hydrogens with a +1 charge each *phew*

they combine with sulphate ion to make Hydrogen sulphate, whose Oxidation number NOW is 32

 

and we know 8 fits in there perfectly.

now this really does take a lot longer to type out here and read than it actually takes to do!

with a little practice it`s VERY easy!

I will also point out that this is only a General Guide, and NOT the letter of the Law!

[thedarkshade]

Electronegativity is the ability of the atoms of any element to attract the mutual electronic couple near itself. It is due to changes in electronegativity that water is a polarized molecule. Oxygen has a high electronegativity value (the highest after F) and because of that it takes the mutual electronic cuple nearer to himself and is negatively charged ([math]\sigma -[/math]. And as the couple is moving away from hydrogen, then hydrogen gets positively charged ([math]\sigma +[/math]). And that makes the water possible to create hydrogenic bonds and makes water a key substance!

 

Back to beginning:

 

There are some rules that should be followed in order not to have problems with redox equations and not to have problems with finding out the oxidation numer:

 

1. Hydrogen is always +1, only in hydrores (NaH, LiH, CaH2 etc..) where his oxidation number is -1.

2. The oxidation number of oxygen is -2, except in peroxides where it is -1

3. The oxidation number of elements in elementary conditions is always 0

4. The oxidation number of a molecule should always me 0

 

By following these rules you can very easily find out the oxidation number and equalize tricky equations.

 

Cheers,

Shade

[foodchain]

electronegativity is EVERYTHING to do with it, but it`s not a workable "unit" as such, so Oxidation state or Valency (when I was taught) is used, less so Valency now though.

 

effectively the "magic" number is 8, and you need a Periodic table (or a good memory) to know what each element is in way of electron count.

 

you simply look at what group it`s in and there`s your answer, although it gets a bit more interesting when you get to the Middle groups as they CAN swing either way (esp Group 4).

 

they can be the Oxidiser Or reducer

 

think Calcium Carbide or Carbon dioxide for instance, the Carbon plays 2 different roles here.

 

but lets use an example given in the OP and look at H2SO4.

 

H=1 (but we have 2 so that 1x2=2)

S= 6

O=6 (but we have 4 of them so it`s really 6x4=24)

 

so lets add them add them up as Ions SO4 (the sulphate ion) adds up to 24+ 6 and that`s 30

 

so how many 8`s go into 30? well we know it goes into 32 4 times, so it`s 3 remainder 2, so we can scrap the 3 as that obeys the rules and we don`t need it anymore, we want the Remainder!

 

we also know the SO4 is the Oxidiser (it`s way over on the left on the periodic table) so it`s Overall charge is -2 (remember the remainder?).

 

Happily we have those pair of Hydrogens with a +1 charge each *phew*

they combine with sulphate ion to make Hydrogen sulphate, whose Oxidation number NOW is 32

 

and we know 8 fits in there perfectly.

now this really does take a lot longer to type out here and read than it actually takes to do!

with a little practice it`s VERY easy!

I will also point out that this is only a General Guide, and NOT the letter of the Law!

 

That’s just the thing, its not that I cant remember the octet rule or what not, or the funny question of asking people what anhydrous means. Its that they would just say satisfy the octet rule for instance in some drawing, Lewis dots and what not... to me I just really wanted to know what was going on. it hit me to the first time i tried to do it just from a math perspective such as using just ratios of masses or what not, and so i got frustrated. then I ran into that whole electronic configuration bit on my own, reading about s,p,d,f and all that stuff and such started to make a lot more sense. I mean sitting in a class and trying to think on an issue when they give you a crumb of the picture just sucks. To be honest my first thought was that the mechanism sort of mimicked a seesaw:D , so for me as a student I really have to know it all or it simply does not make any sense to me, I don’t want to know short cuts, or tricks of the trade, I really just want to know why something or some phenomena is actually occurring.