NEET Chemistry Some Basic Concepts of Chemistry / रसायन की कुछ मूलभूत अवधारणाएँ NEET PYQ-Some Basic Concepts Chemistry

  • question_answer
    *1.0 g of magnesium is burnt with 0.56 g \[{{O}_{2}}\] in a closed verssel. Which reactant is left in excess and how much?                                                                                                                                     [AIPMT 2014] \[(At.wt.Mg=24;O=16)\]

    A)  \[Mg,0.16g\]       

    B)       \[{{O}_{2}}.0.16g\]

    C)  \[Mg,0.44g\]       

    D)       \[{{O}_{2}},0.28g\]

    Correct Answer: A

    Solution :

    The balanced chemical equation is
    \[\underset{\begin{smallmatrix}   \\    \\  24g \end{smallmatrix}}{\mathop{Mg}}\,+\underset{\begin{smallmatrix}   \\  16g \end{smallmatrix}}{\mathop{\frac{1}{2}{{O}_{2}}}}\,\xrightarrow{\,}\underset{\begin{smallmatrix}   \\    \\  40g \end{smallmatrix}}{\mathop{MgO}}\,\]
    From the above equation, it is clear that,
    24 g Mg reacts with 16 g \[{{O}_{2}}.\]
    Thus, 1.0 g Mg reacts with
    \[\frac{16}{24}\times 0.67g\,{{O}_{2}}=0.67g\,{{O}_{2}}.\]
    But only 0.56 g \[{{O}_{2}}\] is available which less than 0.67 g is. Thus, \[{{O}_{2}}\] is the limiting reagent.
    Further, 16 g \[{{O}_{2}}\] reacts with Mg 24 g.
    \[\therefore \] 0.56 g \[{{O}_{2}}\] will react with Mg
    \[=\frac{24}{16}\times 0.56=0.84g\]
    \[\therefore \] Amount of Mg left unreacted
    = 1.0 - 0.84g Mg = 0.16g Mg
    Hence, Mg is present in excess and 0.16 g Mg is left behind unreacted.


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