what kind of sums would come in neet for topic BALANCING REACTIONS BY OXIDATION METHOD, where you have to add,water and h2 molecules, etc?
I dnt know how would they frame query.
give me examples for that kind of sums with solutions please.
1) Oxidation Number Method
· The composition and formulae must be known for the reactants and products while writing equations for oxidation–reduction reactions.
· The following steps need to be used for balancing the equations.
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· Write the net unbalanced equation with the correct formula for each reactant and product.
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· Identify the atoms which undergo a change in the oxidation number in the reaction by assigning the oxidation number to all elements in the reaction.
· Calculate the increase or decrease in the oxidation number per atom and for the entire molecule or ion in which it occurs.
· If these are not equal, then multiply by suitable coefficients so that these become equal.
· If two substances are reduced and nothing is oxidised or vice versa, then something is wrong.
· Either the oxidation numbers have not been assigned properly or the formulae of reactants or products are wrong.
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· Ensure the involvement of ions if the reaction is taking place in water.
· Add H+ or OH− ions to the equation on the appropriate side so that the total ionic charges of reactants and products are equal.
· Use H+ ions in the equation if the reaction is carried out in acidic solution.
· Use OH− ions in the equation if the reaction is carried out in basic solution.
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· In the equation, make the numbers of hydrogen atoms equal by adding water (H2O) molecules to the reactants or products on the two sides.
· Check the number of oxygen atoms also.
· If the number of oxygen atoms is the same in the reactants and products, then the equation represents a balanced redox reaction.
Example 1:
· Permanganate ion reacts with bromide ion in the basic medium to give manganese dioxide and bromated ion.
o 
Step 1: The skeletal ionic equation is
o 
Step 2: Assign oxidation numbers for Mn and Br
+7 −1 +4 +5
This indicates that the permanganate ion is the oxidant and the bromide ion is the reductant.
o Step 3: Calculate the increase and decrease of the oxidation number and make the increase equal to the decrease.
+7 −1 +4 +5
o Step 4: As the reaction occurs in the basic medium and the ionic charges are not equal on both sides, add 2 OH− on the right to make the ionic charges equal.
o Step 5: Finally, count the hydrogen atoms and add the appropriate number of water molecules, i.e. one H2O molecule on the left side to achieve a balanced redox change.
Example 2:
· Reaction of potassium dichromate (VI) (K2Cr2O7) with sodium sulphite (Na2SO3) in an acid solution to give the chromium (III) ion and the sulphate ion.
o Step 1: The skeletal ionic equation is
o Step 2: Assign oxidation numbers for Cr and S
+6 −2 +4 −2 +3 +6 −2
This indicates that the dichromate ion is the oxidant and the sulphite ion is the reductant.
o Step 3: Calculate the increase and decrease of the oxidation number and make them equal.
+6 −2 +4 −2 +3 +6 −2
o 
Step 4: As the reaction occurs in the acidic medium and the ionic charges are not equal on both sides, add 8H+ on the left to make ionic charges equal.
o Step 5: Finally, count the hydrogen atoms and add the appropriate number of water molecules (4H2O) on the right side to achieve the balanced redox reaction.
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