Question #20e6a

1 Answer
Mar 6, 2017

Answer:

Here's what I got.

Explanation:

Start with what you know for sure, which is that oxygen has an oxidation number of #color(blue)(-2)# in almost all the compounds it forms.

Remember that the sum of the oxidation numbers of each atom that is part of a compound must be equal to the net charge of said compound.

For water, you will have

#"H"_ 2 stackrel(color(blue)(-2))("O")#

Since you have #2# hydrogen atoms, you will need an oxidation state of #color(blue)(+1)# for each of them to get

#2 xx (+1) + 1 xx (-2) = 0#

Therefore, you will have

#stackrel(color(blue)(+1))("H")_ 2 stackrel(color(blue)(-2))("O")#

Do the same for sulfur dioxide. You will have

#"S" stackrel(color(blue)(-2))("O")_2#

Since you have #2# oxygen atoms here, you will need an oxidation state of #color(blue)(+4)# for the sulfur atom to get

#1 xx (+4) + 2 xx (-2) = 0#

Therefore, you will have

#stackrel(color(blue)(+4))("S")stackrel(color(blue)(-2))("O")_2#

Finally, move on to the permanganate ion, #"MnO"_4^(-)#. You will have

#"Mn" stackrel(color(blue)(-2))("O") _4""^(-)#

This time, the ion sum of the oxidation numbers must be equal to #-1# since that is the net charge of the ion. You will need an oxidation state of #color(blue)(+7)# for the manganese atom to get

#1 xx (+7) + 4 xx (-2) = -1#

Therefore, you will have

#stackrel(color(blue)(+7))("Mn") stackrel(color(blue)(-2))("O") _4""^(-)#