RAJASTHAN PMT Rajasthan - PMT Solved Paper-2008

  • question_answer
    How many unit cells are present in a cube shaped ideal crystal of \[NaCl\] of mass\[1.00\,\,g\]? [Atomic masses:\[Na=23,\,\,Cl=35.5]\]

    A) \[2.57\times {{10}^{21}}\]                           

    B)        \[5.14\times {{10}^{21}}\]

    C)        \[1.28\times {{10}^{21}}\]                           

    D)        \[1.71\times {{10}^{21}}\]

    Correct Answer: A

    Solution :

    Mass of one unit-cell\[(m)=\]volume\[\times \]density                                                  \[={{a}^{3}}\times d\]                                                  \[={{a}^{3}}\times \frac{MZ}{{{N}_{0}}{{a}^{3}}}=\frac{MZ}{{{N}_{0}}}\]                                            \[m=\frac{58.5\times 4}{6.02\times {{10}^{23}}}g\] \[\therefore \]Number of unit cells in\[1\,\,g=\frac{1}{m}\]                              \[=\frac{6.02\times {{10}^{23}}}{58.5\times 4}=2.57\times {{10}^{21}}\]


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