Punjab Medical Punjab - MET Solved Paper-2007

  • question_answer
    \[Zn\]gives \[{{H}_{2}}\] gas with \[{{H}_{2}}S{{O}_{4}}\] and \[HCl\] but not with \[HN{{O}_{3}}\]

    A)  \[Zn\]act as oxidising agent when react with\[HN{{O}_{3}}\]

    B)  \[HN{{O}_{3}}\]is weaker acid than \[{{H}_{2}}S{{O}_{4}}\] and \[HCl\]

    C)  In electrochemical series \[Zn\] is above hydrogen

    D)  \[NO_{3}^{-}\] is reduced in preference to hydronium ion

    Correct Answer: D

    Solution :

    \[Zn\]is present above \[{{H}_{2}}\] in electrochemical series. So, it liberates hydrogen gas from dilute\[HCl/{{H}_{2}}S{{O}_{4}}\]. But \[HN{{O}_{3}}\] is oxidising agent. The hydrogen obtained in this reaction is converted into\[{{H}_{2}}O\]. In \[HN{{O}_{3}},\,\,NO_{3}^{-}\] ion is reduced and give \[N{{H}_{4}}N{{O}_{3}},\,\,{{N}_{2}}O,\,\,NO\] and \[N{{O}_{2}}\] (based upon the concentration of\[HN{{O}_{3}}\]) \[[Zn+\underset{(nearly\,\,6%)}{\mathop{2HN{{O}_{3}}}}\,\xrightarrow{{}}Zn{{(N{{O}_{3}})}_{2}}+2H]\times 4\]                 \[HN{{O}_{3}}+8H\xrightarrow{{}}N{{H}_{3}}+3{{H}_{2}}O\]                 \[N{{H}_{3}}+HN{{O}_{3}}\xrightarrow{{}}N{{H}_{4}}N{{O}_{3}}\]                 \[4Zn+10HN{{O}_{3}}\xrightarrow{{}}4Zn{{(N{{O}_{3}})}_{2}}\]


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