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CMC Medical CMC-Medical Ludhiana Solved Paper-2009

  • question_answer
    The formula mass of Mohrs salt is 392. The iron present in it is oxidised by \[KMn{{O}_{4}}\]in acid medium. The equivalent mass of Mohrs salt is

    A)  392                                       

    B)  31.6

    C)  278                                       

    D)  156

    Correct Answer: A

    Solution :

                    Mohrs salt is\[{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\cdot FeS{{O}_{4}}\cdot 6{{H}_{2}}O.\] The equation is: \[5F{{e}^{2+}}+MnO_{4}^{-}+8{{H}^{+}}\xrightarrow{{}}\]\[5F{{e}^{3+}}+M{{n}^{2+}}+4{{H}_{2}}O\] Total change in oxidation number of iron \[=(+3)-(+2)\] \[=+\,1\] So, equivalent wt. of Mohrs salt \[=\frac{\text{Mol}\text{. wt}\text{. of Mohr}\,\text{ }\!\!\!\!\text{ s salt}}{\text{1}}\] \[=\frac{392}{1}\] \[=392\]


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