CH3: Redox I

Question 1

Rules to determine oxidation number ?

Answer 1

1. All uncombined elements/ elements that are bonded to identical atoms have oxidation number 0
   E.g O2 - ox number= 0
   Ag - ox number = 0
2. Oxidation number of monatomic ion is same as its charge
   Na+ = +1 so ox number is +1
3. For molecular ions (group of atoms with overall charge) , the sum of the oxidation numbers is same as overall charge of ion
   E.g SO4 : oxygen has OX number -2 , but there are 4 oxygens , so 4 x -2 = -8
   S has OX number +6
   6+-8 = -2
4. Hydrogen always has OX number +1 , EXCEPT :
   - in metal hydrides ( -1) - e.g hydrogen chloride
   - molecular hydrogen (0) - H2
5. Oxygen always has OX number -2 EXCEPT :
   - in peroxides (O2 2-) , it is -1
   - molecular oxygen (o2) , it is 0
6. In a compound/ion, the more electronegative element is given the Ox no.
   Al is always 3+
   F is always -1

Question 2

What is an oxidising /reducing agent?

Answer 2

OXIDISING : gains electrons itself(reduced itself) / oxidises other atoms (makes them lose electrons)
REDUCING : lose electrons itself (OXIDISED) / reduces other atoms (makes them gain electrons)

Question 3

What is a disproportionation reaction?

Answer 3

Reaction which the same species is simultaneously oxidised/reduced

Question 4

What happens to OX number when oxidised and reduced?

Answer 4

OX number INCREASE if oxidised
OX number DECREASE if reduced