A redox couple is defined as having together the oxidised and reduced forms of a substance taking part in an oxidation or reduction half reaction. Permanganate ion reacts with bromide ionin basic medium to give manganese dioxide and bromate ion. Write the balanced ionic equation for the reaction.
Step 1: The skeletal ionic equation is:
Step 2: Assign oxidation numbers for Mn and Br
+7 -1 +4 +5
Step 3: Calculate the increase and decrease of oxidation number, and make the increase equal to the decrease.
Step 4: As the reaction occurs in the basic medium, and the ionic charges are not equal on both sides, add 2 OH– ions on the right to make ionic charges equal.
Step 5: Finally, count the hydrogen atoms and add appropriate number of water molecules (i.e. one H2O molecule) on the left side to achieve balanced redox change.
Justify that the reaction: is a redox change.
Since in the above reaction the compound formed is an ionic compound, which may also be represented as Na+H– (s), this suggests that one half reaction in this process is :
and the other half reaction is:
This splitting of the reaction under examination into two half reactions automatically reveals that here sodium is oxidised and hydrogen is reduced, therefore, the complete reaction is a redox change.