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8.4 " mL of " gaseous hydrocarbon A was burnt with 50 " mL of " O_2 in a eudiometer tube. The volume of the products after cooling to room temperature was 37.4 mL. When reacted with NaOH, the volume contracted to 3.8 mL. What is the molecular formula of A.

Answer» <html><body><p></p>Solution :Let the formula of hydrocarbon `(A)=C_(x)H_(y)` <br/> `thereforeundersetunderset(8.4)(1 vol) (C_(x)H_(y)(g))+undersetunderset(8.4(x+(y)/(4))(vol)(x+(y)/(4))vol)((x+(y)/(4))O_(2)(g))toundersetunderset(8.4 x vol)(x vol)(xCO_(2)(g))+(y)/(2)H_(2)(g)` <br/> Contraction in volume `=V_(<a href="https://interviewquestions.tuteehub.com/tag/r-611811" style="font-weight:bold;" target="_blank" title="Click to know more about R">R</a>)-V_(P)` <br/> `=(8.4+50)-(37.4)` <br/> `=21mL` <br/> From equation the contraction is (volume of `H_(2)O` is not taken as it condenses) <br/> `therefore` Contraction`=(8.4[1+(cancel(x)+(y)/(4))-(cancel(x)+0)]` <br/> `implies8.4(1+(y)/(4))=21impliesy=6` <br/> After treating with `NaOH`, there is a contraction of `(37.4-3.8)=33.6mL` which is equal tot he <a href="https://interviewquestions.tuteehub.com/tag/vlume-3264243" style="font-weight:bold;" target="_blank" title="Click to know more about VLUME">VLUME</a> of `CO_(2)` produced. <br/> Volume of `CO_(2)` produced by `8.4 mL` of hydrocarbon `=8.4x` <br/> `therefore8.4x` <br/> `therefore 8.4x=33.6` <br/> `ximplies4mL` Alternate <a href="https://interviewquestions.tuteehub.com/tag/method-559432" style="font-weight:bold;" target="_blank" title="Click to know more about METHOD">METHOD</a>: <br/> After `NaOH` tretment, the volume is reduced to `3.8 mL`, which <a href="https://interviewquestions.tuteehub.com/tag/corresponds-935737" style="font-weight:bold;" target="_blank" title="Click to know more about CORRESPONDS">CORRESPONDS</a> to the volume of `O_(2)` usused. Volume of `O_(2)` (unused)`=`volume of `O_(2)` taken`-` volume of of `O_(2)` used <br/> `implies50-8.4(x+(y)/(4))=3.8` <br/> Sove to get, `y=6` <br/> Hence, hydrocarbon is `C_(4)H_(6)`.</body></html>


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