NEET Chemistry States of Matter / पदार्थ की अवस्थाएँ - गैस एवं द्रव Question Bank Self Evaluation Test - States of Matter

  • question_answer
    When 2 g of a gas A is introduced into an evaluated flask kept at \[25{}^\circ C\], the pressure is found to be one atmosphere. If \[3gm\] of another gas B is then added to the same flask, the total pressure becomes 1.5 atm. Assuming ideal gas behaviour, calculate the ratio of the molecular weights \[{{M}_{A}}:{{M}_{B}}.\]      

    A) 1:3                               

    B) 1:1  

    C) 2:1                              

    D) 3:1

    Correct Answer: A

    Solution :

    [a] From ideal gas equation, \[PV=nRT\] \[PV\left( \frac{m}{M} \right)RT\,or\,M=m\frac{RT}{PV}\] Let the molecular wt. of A and B be \[{{M}_{A}}\] and \[{{M}_{B}}\] respectively. Then \[{{M}_{A}}=2\times \frac{RT}{1\times V};\,{{M}_{B}}=\frac{3\times RT}{0.5\times V}\] \[\therefore \frac{{{M}_{A}}}{{{M}_{B}}}=\frac{2RT}{V}\times \frac{0.5V}{3RT}=\frac{2\times 0.5}{3}=\frac{1}{3}\] Therefore, the ratio \[{{M}_{A}}:{{M}_{B}}=1:3\]


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