Question

In an oxidation reduction reaction, dichromate $ (C{{r}_{2}}O_{7}^{2-}) $ ion is reduced to $ C{{r}^{3+}} $ ion. The equivalent weight of $ {{K}_{2}}C{{r}_{2}}{{O}_{7}} $ in this reaction is molecular weight

• A. $ \frac{molecular\,\,weight}{3} $
• B. $ \frac{molecular\,\,weight}{6} $
• C. $ \frac{molecular\,\,weight}{1} $
• D. $ \frac{molecular\,\,weight}{2} $

Answer 1

Answer: (B)

$ \overset{+6}{\mathop{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}\,+4{{H}_{2}}S{{O}_{4}}\xrightarrow{{}}{{K}_{2}}S{{O}_{4}}+\overset{+3}{\mathop{C{{r}_{2}}}}\,{{(S{{O}_{4}})}_{3}} $ $ +4{{H}_{2}}+3[O] $ Equivalent weight $ =\frac{Molecular\,\,weight}{\begin{align} & Change\,\,in\,\,oxidation\,\,number\,\,of\,\,atoms \\ & \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,present\,\,in\,\,one\,\,molecular \\ \end{align}} $ $ \therefore $ Equivalent weight $ =\frac{Molecular\,\,weight}{2\times 3} $ $ =\frac{Molecular\,\,weight}{6} $