Urgently need help on a caluculating molecular formula of CxHy(alevel)

Hey everyone i am stuck with a question i found out what x is but i don't know what to do next (de nada)

Hey everyone i am stuck with a question i found out what x is but i don't know what to do nect

Find y ...

Sorry for the delay had troubles adding the image on to the thread ( working out is slightly messy but the x looks like times) in the answers they work out x and y in terms of volume i don't know why?

You've got x correct.

To find y you must consider that the volume of water formed is negligible and so the only way is via logic, considering the changes in volume.

If the initial volume of oxygen is v, then the total initial volume of gas = (v + 10)

Which means that the total final volume of gas = (v + 10 - 20) = (v -10)

And you have already identified that there is 40 cm³ of carbon dioxide formed (as x = 4) and that the water volume is zero (it's a liquid under these conditions)

So that the excess oxygen must be (v - 10 - 40) = (v - 50)

So the initial volume of oxygen was v and the final volume is (v-50) so that 50 cm³ of oxygen reacted

You know that 40cm³ of oxygen was needed to react with C₄ of the compound, therefore the other 10cm³ must have reacted with the hydrogen from 10cm³ of the hydrocarbon.

4H + O₂ ==> 2H₂O

Therefore H = 4

C₄H₄

/* ----------------------------------------------------------------*/

Checksum:

C₄H₄ + 5O₂ ==> 4CO₂ + 2H₂O

initial volumes 10 ...................... v ....................................40 .........................0 ............... unreacted oxygen (v - 50)

initial volume total = (v+10)
final volume total = (v-10)
---------------------------
contraction 20cm³

Beautifully explaned thanks XD i have one small doubt what gases make up 20cm3