Determine the oxidation number of chlorine in the reactant...

Question

KClO3 (s) --> KCl (s) O2

I know the answer is 5 but i have no idea why, please help me =(

Answer 1

Oxygen has an oxidation number of -2

Since there are 3 oxygens in the reactant the oxidation number becomes -6

Potassium (K) has an oxidation number of +1

Add the oxidation numbers together: 1 + -6 or basically 1 - 6 = -5

There is no charge on this molecule so the oxidation numbers of all elements added together must be 0

So far the oxidation number is -5 so the only number that chlorine can be to make the molecule 0 is +5

So the oxidation number of chlorine in the reactant is +5

Answer 2

Remember when calculating oxidation numbers, the yardstick is

OXYGEN is always '-2'

As there are three oxygen's in KClO3 then the oxidation value for the three oxygen's is  3 x -2 = -6

As KClO3 is a neutrally charged molecule and the oxygen moiety is '-6' then the 'KCl' moiety must be +6

That is +6 - 6 = 0

However 'K' only ever oxidises one electron to form 'K^+' hence its oxidation number is '+1'. So the remaining '+5' must lie on the chlorine.

Answer 3

Potassium , K is in group 1A which means it has a "valence " of +1. That means that the radical ClO3 must have a net charge of -1 to have a neutral molecule. Oxygen is in group 6 A which means it principally wants to gain 2 electrons  to make an octet so it will have a common "valence " of -2   since the ClO3 has 3 oxygens and each is -2      3 X -2 = -6..if the whole radical has a charge of -1then the Cl has to be + 5   ( +5) + ( -6) = -1