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CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2006

  • 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 \[{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\,.\,\,FeS{{O}_{4}}\,.\,6{{H}_{2}}O\] 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 Mohfs salt                                 \[=\frac{Mol.\text{ }wt.\text{ }of\text{ }Mohrs\text{ }salt}{1}\]                 \[=\frac{392}{1}\]                 \[=392\]


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