JEE Main & Advanced Chemistry The Solid State / ठोस प्रावस्था Question Bank Mock Test - Solid State

  • question_answer
    A mineral of iron contains an oxide containing 72.36% iron by mass and has a density of 5.2 g/cc. Its unit cell is cubic with edge length of 839 pm. What is the total number of atoms (ions) present in each unit cell? (Fe-56, O-16)

    A) 58                    

    B) 57

    C) 56                    

    D) 55

    Correct Answer: C

    Solution :

    [c] \[\frac{Fe}{O}=\frac{72.36}{\frac{56}{\frac{27.64}{16}}}=0.75=\frac{75}{100}=\frac{3}{4}\] \[\therefore F{{e}_{3}}{{O}_{4}}=3\times 56+4\times 16=32\] Density=\[\frac{Mass}{Volume}\] \[\Rightarrow \]Mass of 1 unit cell=Density \[\times {{N}_{A}}\times {{a}^{3}}\]amu \[=5.2\times 6.023\times {{10}^{23}}\times {{(839\times {{10}^{-10}})}^{3}}\] \[=1842\]amu No. of atoms\[=\frac{1842}{232}\times 7=56\]


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