Gujarat BoardEnglish MediumSTD 11 ScienceChemistryRedox Reactions1 Mark
Question
Justify that the following reactions are redox reactions:$4BCl_3(g) + 3LiAlH_4(s) → 2B_2H_6(g) + 3LiCl(s) + 3AlCl_3(s)$
✓
Answer
$4BCl_{3(g)} + 3LiAlH_{4(s)} → 2B_2H_{6(g)} + 3LiCl_{(s)} + 3AlCl_{3(s)}$The oxidation number of each element in the given reaction can be represented as:
$\stackrel{{+3\ -1}}{4\ \ \ \ \ \hbox{BCl}_{3(\text{g})}}+\stackrel{{+1\ \ +3\ -1}}{3\ \ \ \ \hbox{LiAlH}_{4(\text{s})}}\ \rightarrow\stackrel{{-3}}{2\ \ \hbox{B}_2}\stackrel{{+1}}{\ \ \ \ \ \hbox{H}_{6(\text{g})}}+\stackrel{{+1}}{3\hbox{Li}}\stackrel{{-1}}{\ \ \ \ \hbox{Cl}_{(\text{s})}}+\stackrel{{+3}}{3\hbox{Al}}\stackrel{{-1}}{\ \ \ \ \ \ \hbox{Cl}_{3(\text{s})}}$
In this reaction, the oxidation number of B decreases from +3 in $BCl_3$ to –3 in $B_2H_6.$ i.e., $BCl_3$ is reduced to $B_2H_6$. Also, the oxidation number of H increases from $–1 in LiAlH_4 to +1 in B_2H_6 i.e., LiAlH_4$ is oxidized to $B_2H_6.$ Hence, the given reaction is a redox reaction.
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