CET Karnataka Engineering CET - Karnataka Engineering Solved Paper-2006

  • question_answer
    The brown ring test for nitrates depends on :

    A)  the reduction of nitrate to nitric oxide

    B)  oxidation of nitric oxide to nitrogen dioxide

    C)  reduction of ferrous sulphate to iron

    D)  oxidising action of sulphuric acid

    Correct Answer: A

    Solution :

    The brown ring is obtained due to the formation of pentaaquanitrosonium ion. In this reaction reduction of nitrate ion by \[F{{e}^{2+}}\] ion takes places as                 \[NO_{3}^{-}+3F{{e}^{2+}}+4{{H}^{+}}\xrightarrow{{}}\]                                                 \[NO+3F{{e}^{3+}}+2{{H}_{2}}O\] \[F{{e}^{2+}}+NO+5{{H}_{2}}O\xrightarrow{{}}\underset{Brown\text{ }complex}{\mathop{{{[Fe{{({{H}_{2}}O)}_{5}}NO]}^{2+}}}}\,\]


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