[Kaleyrvt]

Hey all-
Trying to figure out if I am doing this right-doing a chem course via correspondance
 Basically need to see if I am on the right track with these???
78)   Determine the oxidation numbers of the underlined elements in the following
formulas:

a) KClO3  =>   1+  +  x  =  3 x 2-
      1+  +  x  =  6-
      1+  +  x   +  6-  =  0
      Cl = x = 5+
       
b) NH4+    =>   x  +  4  x    1+
      x  +  4+           
      x  +  4+  =  0
      N = x =  4-
                  
c) Cr2O72-  =>   x  +  7 x 2-
      x  +  14-
      x  +  14- =  0
      Cr = x = 14+

d) MnO42-  =>   x  +  4 x 2-
      x  +  8-
      x  +  8- =  0
      Mn = x = 8+

Is this the right way to do this?? i have a feeling I am doing it wrong...Please give me any feedback possible
Thanks

[Dan]

a) is correct, you have the right idea, but for the others you must take into account the overall charge of the ion.

eg. for b), you say x + 4+ = 0. This is incorrect, it's not equal to 0, it should be something else...

[DevaDevil]

And for c), don't forget there are 2 Cr atoms in the compound

[Borek]

1+  +  x  =  3 x 2-
1+  +  x  =  6-
1+  +  x   +  6-  =  0

Finally, you better check your math...

[Kaleyrvt]

I am confused
 

[chiralic]

Hint: The neutral compound or element, the sum of the oxidation states is zero

Also check this link: http://www.chemguide.co.uk/inorganic/redox/oxidnstates.html (check section Examples of working out oxidation states)

You can use the keywords oxidation number or oxidation state on google and you'll get information and examples related with your post

[Kaleyrvt]

iS THIS BETTER??? Hopefully..

b) NH4+    =>x  +  4 (1+) = 1+
       x  +  4+  = 1+         
       N = x =  -3



c) Cr2O7 2-  =>2 x  +  7(2-)= 2-
         2x  +  14- =2-
        Cr = x = +6

D)MnO4 2-  =>   x  +  4 x 2- = 2-
      x  +  8- =2-
      Mn = x = +6

[Borek]

Much better. Although I think it will be even better to use slightly different notation - instead of

2x + 7(2-) = 2-

put it as

2x + 7*(-2) = -2

This way it is not only OK chemically (assuming ON are OK) but it also makes a mathematical sense.

[Dan]

Yes your answers are correct. * for multiply avoids confusion, as you are using x as an algebraic symbol.