Uncategorized40 ml of a hydrocarbon undergoes combustion in 260ml of oxygen and gives 160ml of CO2 . If all volumes are measured under similar conditions of temperature and pressure, the formula of the hydrocarbon is?

40 ml of a hydrocarbon undergoes combustion in 260ml of oxygen and gives 160ml of CO2 . If all volumes are measured under similar conditions of temperature and pressure, the formula of the hydrocarbon is?

  1. A

    C3H8

  2. B

    C4H8

  3. C

    C6H14

  4. D

    C4H10

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    Solution:

     CXH4+x+y4O2xCO2+y2H2O 40 ______260ml           160ml  

    At constant temperature and pressure (at STP), volume is proportional to moles.


    Hence, the combustion of 1 mole of hydrocarbon will require 6.5 moles (260/40​=6.5)  of oxygen and will produce 4 moles (160/​40=4) of carbon dioxide.

    i,e x=4
    Thus, the molecular formula contains 4 carbon atoms.

    x+y/4​=6.5

    y=10 

    Thus, the molecular formula contains 10 hydrogen atoms.

    Out of 6.5 moles of oxygen, 4 moles will combine with carbon to form 4 moles of carbon dioxide.
    The remaining 2.5 moles of oxygen will combine with 10 moles of hydrogen atoms (from the hydrocarbon) to form 5 moles of water.

    The hydrocarbon is C4​H10 and the combustion reaction is C4​H10​+6.5O2​→4CO2​+5H2​O.
     


     

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