KVPY Sample Paper KVPY Stream-SX Model Paper-29

  • question_answer
    Which of the following combination will produce \[{{\operatorname{H}}_{2}}gas?\]

    A) Fe metal and cone. \[HN{{O}_{3}}\]

    B) Cu metal and cone. \[HN{{O}_{3}}\]

    C) Zn metal and \[NaOH\text{ }(aq)\]

    D) Au metal and \[NaCN\text{ }(aq)\] in the presence of air

    Correct Answer: C

    Solution :

    Fe becomes passive on reaction with concentrated\[HN{{O}_{3}}\]. However, cold relatively cone.\[{{\operatorname{HNO}}_{3}}\], reacts with Fe as below.
    \[Fe+6HN{{O}_{3}}\to Fe{{\left( N{{O}_{3}} \right)}_{3}}+3N{{O}_{2}}+3{{H}_{2}}O\]
    \[Fe+6HN{{O}_{3}}\to Fe{{\left( N{{O}_{3}} \right)}_{3}}+3N{{O}_{2}}+3{{H}_{2}}O\]\[+2{{H}_{2}}O\]
    \[4Au+8NaCN+{{O}_{2}}+2{{H}_{2}}O\to \]\[4Na[Au {{(CN)}_{2}}]+ 4NaOH\]
    \[Zn+2NaOH\to N{{a}_{2}}Zn{{O}_{2}}+{{H}_{2}},\]

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