1.

Write the skeleton equation for the followingchemical reaction and balance them by oxidation number method : (i) Chloride ions reduce manganese dioxide to manganese (II) ions in acidic medium and get itself oxidized to chlorine gas . (ii) The nitrate ions in acidic medium oxidize magnesium to Mg^(2+) ions but itself gets reduced to nitrous oxide .

Answer»

Solution :(i) The skeleton EQUATION for the given process is
`MnO_(2) + Cl^(-) to Mn^(2+) + Cl_(2) + H_(2)O`
Step (1) : `overset(+4)Mnoverset(+2)O_(2) + Cl^(-) to Mn^(2+) + overset(0)Cl_(2) + overset(+1)H_(2) overset(-2)O`
Step (2) :

Step (3) : Equalize the increase/decrease in O.N. by multiplying
`MnO_(2) " by 1 and" Cl^(-) " by " 2 `
` MnO_(2) + 2Cl^(-) to Mn^(2+) + Cl_(2) + H_(2)O`
Step (4): Balanceother atoms except H and O. Here they are all balanced .
Step(5) : Balance O atoms by adding `H_(2)O` molecules to the SIDE falling short of O atoms
`MnO_(2) + 2Cl^(-) to Mn^(2+) + Cl_(2) + H_(2)O + H_(2)O`
Step (6) : Balance H atoms by adding `H^(+)` ions to the side falling short of H atoms.
`MnO_(2) + 2Cl^(-) + 4H^(+) to Mn^(2+) + Cl_(2) + 2H_(2)O`
(ii) The skeleton equation for the given process is
`MG + NO_(3)^(-) to Mg^(2+) + Na O + H_(2)O`
Step (1) : `overset(0)Mg + (overset(+5)Noverset(-2)O_(3))^(-) to Mg^(2+) + overset(+1)N_(2) overset(-2)O + overset(+1)H_(2) overset(-2)O `
Multiply `NO_(3)^(-)` by 2 to equalize N atom
Step (2) :

Step (3) : Equalize increase /decrease in O.N. by multiplying Mg by 4 and `2NO_(3)^(-)` by 1 .
`4Mg + 2NO_(3)^(-) to 4Mg^(2+) + N_(2)O + H_(2)O`
Step (4) : Balance atoms other than O and H
`4Mg + 2NO_(3)^(-) to 4Mg^(2+) + N_(2)O + H_(2)O`
Step (5) : Balance O atoms
`4Mg + 2NO_(3)^(-) to 4Mg^(2+) + N_(2)O + H_(2)O + 4H_(2)O`
Step (6) : Balance H atoms as is done in acidic medium
`4Mg + 2NO_(3)^(-) + 10H^(+) to 4Mg^(2+) + N_(2)O + 5H_(2)O`


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