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Redox Reactions — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryRedox Reactions2 Marks
Question
Permanganate ion reacts with bromide ion in basic medium to give manganese dioxide and bromate ion. Write the balanced chemical equation for the reaction.
✓

Answer

Step 1:$\text{MnO}_4^-\text{(aq)}+\text{Br}\text{(aq)}\xrightarrow{ \ \ \ \ \ }\text{MnO}_2\text{(aq)}+\text{BrO}_3^-\text{(aq)}\\ \ +7\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ -1\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ +4\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ +5$
Step 2: $MnO _4^{-}$is oxidant because its oxidation state is decreasing. $Br ^{-}$is reductant because its oxidation state is increasing.
Step 3: Oxidation state of Mn is decreasing by 3 . Oxidation state of Br is increasing by 6 . To equalize increase and decrease, multiply $MnO _4^{-}$by 2 and $Br ^{-}$by 1 we get.
$2 MnO_4^{-}(aq)+Br^{-}(aq) \longrightarrow MnO_2(s)+Br_2^{-}(aq)$
Step 4: Now for balncaing oxygen, we add 1 molecule of $H _2 O$ on RHS.
$2 MnO_4^{-}(aq)+Br^{-}(aq)$
$\longrightarrow MnO_2(s)+BrO_3^{-}(aq)+H_2 O(l)$
Step 5: As the reaction is taking place in basic medium to balance hydrogen, add $2 H _2 O$ molecules on LHS and $2 OH ^{-}$on RHs.
$2 MnO_4^{-}(aq)+Br^{-}(aq)$
$\longrightarrow MnO_2(s)+BrO_3^{-}(aq)+H_2 O(l)+2 OH^{-}(aq)$
It can be seen 1 molecule of $H _2 O$ gets cancelled on both sides, we get.
$2 MnO_4^{-}(aq)+Br^{-}(aq)$
$\longrightarrow MnO_2(s)+BrO_3^{-}(aq)+H_2 O(l)+2 OH^{-}(aq)$
is a balanced equation.

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