moongazer
  • moongazer
K2Cr2O7 + S8 ----> K2O + Cr2O3 + SO2 (the numbers are subscripts) find the oxidation number
Chemistry
  • Stacey Warren - Expert brainly.com
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SOLVED
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chestercat
  • chestercat
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Callisto
  • Callisto
Oxidation number of ..?
moongazer
  • moongazer
all elements there
Callisto
  • Callisto
K -> Group I metal. Either 0, or +1. Here, it's an ion. So, what is the oxidation number of K?

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Callisto
  • Callisto
Btw, I think it's K2Cr2O7 on the left?
moongazer
  • moongazer
yes, there is a typo :)
Callisto
  • Callisto
Okay. What have you got for K?
moongazer
  • moongazer
+1
moongazer
  • moongazer
could you check my answers?
moongazer
  • moongazer
I'll just post it :)
Callisto
  • Callisto
Yup. For both sides, there is no oxidation number change for K. So, K on both sides are +1. Sure :)
moongazer
  • moongazer
I'll just answer it :)
moongazer
  • moongazer
Isn't it that if the subscript of O is greater than 2, it will have an oxidation number of -2 ?
Callisto
  • Callisto
O has an oxidation number of -2 - You're right! :)
moongazer
  • moongazer
but if "O" only it will have -1 and O2 it will have 0?
Callisto
  • Callisto
No, not really. O is in group 6, it need 2 more electrons. So, usually, its oxidation number is -2 when it is bonded to other atoms. If it is an element (i.e. O2), its oxidation number is 0 as element in its own form. But remember, it's just 'usually' when its oxidation number is of -2. There are some exceptions. For instance, if I remember correctly, O in F2O is +2 since F is a more electronegative element and it has an oxidation number of -1. Since there are two F, oxidation number of O has to be +2 in order to get a net oxidation number of the compound equal to zero.
moongazer
  • moongazer
ohh, thanks for the info. Here are my answers :) K2(+1)Cr2(+6)O7(-2) + S8(0) ----> K2(+1)O(-2) + Cr2(+3)O3(-2) + S(0)O2(0) The oxidation number is enclosed by parenthesis.
moongazer
  • moongazer
Is it correct ?
Callisto
  • Callisto
Almost. S(0)O2(0) <- not correct (for both)
moongazer
  • moongazer
K2(+1)Cr2(+6)O7(-2) + S8(0) ----> K2(+1)O(-2) + Cr2(+3)O3(-2) + S(-2)O2(+1)
moongazer
  • moongazer
I made the oxidation number of O2 the unknown. Is it correct now?
Callisto
  • Callisto
Not really. For SO2, O is -2 (you can take a look at O first as it is more electronegative than S!) O2 is NOT an element in this case, so O doesn't have a oxidation number of 0!
moongazer
  • moongazer
K2(+1)Cr2(+6)O7(-2) + S8(0) ----> K2(+1)O(-2) + Cr2(+3)O3(-2) + S(+4)O2(-2) I think this is correct already :)
Callisto
  • Callisto
Nice :)
moongazer
  • moongazer
I'll say something. I'll just fix the laptop :)
moongazer
  • moongazer
please wait :)
Callisto
  • Callisto
Take your time!
moongazer
  • moongazer
Whew! The battery almost got dead. It keeps on saying plugged in, not charging.
moongazer
  • moongazer
So it means, If you have a molecule with an oxygen,to find the oxidation number of the elements in it. You will identify first the more electronegative element and made the charge of it equal to its oxidation number. Then make the oxidation number of the other element the unknown.
moongazer
  • moongazer
you will solve for the unknown oxidation number
Callisto
  • Callisto
Hmm.. you can say so. But when you consider electronegativity of the element, that would be talking about the group V - group VII For metal, it usually has positive oxidation number. If I remember correctly, for group I metal, when it does not exist in element state, it should be of an oxidation number of +1, and looks like it works for most of the group II metal too. But for transition metals, that's another case...
Callisto
  • Callisto
One little practice for you (if you want one lol) Find the oxidation number of H, O and Cl in the compound HOCl.
moongazer
  • moongazer
H(+1)O(-2)Cl(+1)
Callisto
  • Callisto
Yup :D
moongazer
  • moongazer
I hope it is correct. :)
moongazer
  • moongazer
Yey! thanks!
Callisto
  • Callisto
Welcome :)
Callisto
  • Callisto
There are three definitions....
moongazer
  • moongazer
is it the loss of electrons and reactions directly with O2 ?
moongazer
  • moongazer
transfer of electrons?
Callisto
  • Callisto
Definition of oxidation: 1. addition of oxygen to a substance 2. a process in which a substance loses electrons 3. a process in which the oxidation number of an element in a substance increases.
moongazer
  • moongazer
and reduction is the opposite of that?
Callisto
  • Callisto
Yup...
moongazer
  • moongazer
In my notes it says below oxidation it says: +O -H What does "H" have to do with oxidation and reduction ?
Callisto
  • Callisto
-H?!
moongazer
  • moongazer
idk I just saw in my notes. I was late during our class so I didn't know what is H there
moongazer
  • moongazer
Anyway, thank you very much in your time and effort helping me. :)
Callisto
  • Callisto
You're welcome.. Sorry that I couldn't help :(
moongazer
  • moongazer
It's alright you helped me a lot. :)

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