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Question: \(BrO_{3}^{-}\) ion reacts with \(B{{r}^{-}}\) to form \(B{{r}_{2}}\), in acid medium. The equivalen...

BrO3−BrO_{3}^{-} ion reacts with Br−B{{r}^{-}} to form Br2B{{r}_{2}}, in acid medium. The equivalent mass of Br2B{{r}_{2}} in this reaction is:
A. 4M.w.6\dfrac{4M.w.}{6}
B. 3M.w.5\dfrac{3M.w.}{5}
C. 5M.w.3\dfrac{5M.w.}{3}
D. 5M.w.8\dfrac{5M.w.}{8}

Explanation

Solution

We will find the equivalent mass of Br2B{{r}_{2}} in this reaction by the formula of equivalent weight, which is the molar mass divided by the n-factor. n-factor is basically the number of electrons lost and gained in the disproportionation reaction, here the number of these two should be the same.

Complete Solution :
-As we are being provided with the information that BrO3−BrO_{3}^{-} ion reacts with Br−B{{r}^{-}} to form Br2B{{r}_{2}}, in acid medium. We can write the reaction as:
2BrO3−+12H++10e−→Br2+6H2O2BrO_{3}^{-}+12{{H}^{+}}+10{{e}^{-}}\to B{{r}_{2}}+6{{H}_{2}}O
Here, n1{{n}_{1}} = 10
2Br−→Br2+6e−2B{{r}^{-}}\to B{{r}_{2}}+6{{e}^{-}}
Here, n2{{n}_{2}} = 2

- We can see here that this reaction is a disproportionation reaction or we can say redox reaction, where both the oxidation as well as reduction reaction takes place.
- Now, we will find out the n-factor for the above reaction by the formula:
n−factor=n1×n2n1+n2 =10×210+2 =2012 =53 \begin{aligned} & n-factor=\dfrac{{{n}_{1}}\times {{n}_{2}}}{{{n}_{1}}+{{n}_{2}}} \\\ & =\dfrac{10\times 2}{10+2} \\\ & =\dfrac{20}{12} \\\ & =\dfrac{5}{3} \\\ \end{aligned}

- Now, we will find the equivalent weight, which is the molar mass divided by the n-factor.
=M.w.n−factor =M.w.5/3 =3M.w.5 \begin{aligned} & =\dfrac{M.w.}{n-factor} \\\ & =\dfrac{M.w.}{5/3} \\\ & =\dfrac{3M.w.}{5} \\\ \end{aligned}

- Hence, we can conclude that the correct option is (b), that is when BrO3−BrO_{3}^{-} ion reacts with Br−B{{r}^{-}} to form Br2B{{r}_{2}}, in acid medium. The equivalent mass of Br2B{{r}_{2}} in this reaction is 3M.w.5\dfrac{3M.w.}{5}
So, the correct answer is “Option B”.

Note: - As we know that equivalent weight of any compound depends upon the chemical reaction in which it takes place. Basically, equivalent weight is a relative quantity, hence it does not have a unit.
- Whenever, we express the equivalent weight of substance in a unit of grams, then we call it the Gram Equivalent Weight.