JCECE Medical JCECE Medical Solved Paper-2008

  • question_answer
    How many unit cells are present in a cube shaped ideal crystal of \[\text{NaCl}\]of mass 1.00 g? [Atomic masses :\[\text{Na}\,\text{=}\,\text{23,}\,\text{Cl}\,\text{=}\,\text{35}\text{.5}\]

    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) \[\text{=}\,\,\text{volume}\,\text{ }\!\!\times\!\!\text{ }\,\text{density}\] \[={{a}^{3}}\times d={{a}^{3}}\times \frac{Mz}{{{N}_{0}}{{a}^{3}}}=\frac{Mz}{{{N}_{0}}}\] \[m=\frac{58.5\times 4}{6.02\times {{10}^{23}}}g\] \[\therefore \]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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