VMMC VMMC Medical Solved Paper-2007

  • question_answer
    A compound (60 g) on analysis produce carbon, hydrogen and oxygen 24 g, 4 g and 32g respectively. The empirical formula is

    A) \[{{C}_{2}}{{H}_{2}}{{O}_{2}}\]                  

    B) \[{{C}_{2}}{{H}_{4}}{{O}_{2}}\]  

    C) \[C{{H}_{2}}O\]

    D)        \[{{C}_{2}}{{H}_{4}}{{O}_{6}}\]

    Correct Answer: C

    Solution :

    Key Idea: First calculate the percentage of elements, then find relative number of atoms. The relative number of atoms is used to find ratio of atoms, which is infact empirical formula. Given: Mass of compound = 60 g, mass of carbon = 24 g, mass of hydrogen = 4 g, mass of oxygen = 32 g. \[%\,\text{of}\,C=\frac{\text{mass}\,\text{of}\,\text{carbon}}{\text{mass}\,\text{of}\,\text{compound}}\times 100\] \[=\frac{24}{60}\times 100=40%\] \[%\,\text{of}\,\text{H}\,\text{=}\,\frac{\text{mass}\,\text{of}\,\text{hydrogen}}{\text{mass}\,\text{ofcompound}}\times 100\] \[=\frac{4}{60}\times 100=6.66%\] % of \[O=100-(%\,of\,carbon+\,%\,of\,hydrogen)\] \[=100-(40\,+\,6.66)\] \[=100-46.66=53.34%\]                
    Element Percen-tage Atomic mass Relative no. of atoms Ratio
    C 40% 12 \[\frac{40}{12}=3.33\] \[\frac{3.33}{3.33}=1\]
    H \[6.66%\] 1 \[\frac{6.66}{1}=6.66\] \[\frac{6.66}{3.33}=2\]
    O \[53.34%\] 16 \[\frac{53.34}{16}=3.33\] \[\frac{3.33}{3.33}=1\]
    \[\therefore \] Empirical formula \[\text{=C}{{\text{H}}_{\text{2}}}\text{O}\]


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