JCECE Engineering JCECE Engineering Solved Paper-2008

  • question_answer
    How many unit cells are present in a cube shaped ideal crystal of \[NaCl\] \[\text{of}\] 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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