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

Stormragexox
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Hey everyone i am stuck with a question i found out what x is but i don't know what to do nect
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charco
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(Original post by Stormragexox)
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)
Find y ...
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Stormragexox
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(Original post by Stormragexox)
Hey everyone i am stuck with a question i found out what x is but i don't know what to do nect
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Stormragexox
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(Original post by charco)
Find y ...
(Original post by Stormragexox)
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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?
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charco
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(Original post by Stormragexox)
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
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Stormragexox
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(Original post by charco)
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
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charco
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(Original post by Stormragexox)
Beautifully explaned thanks XD i have one small doubt what gases make up 20cm3
Do you mean the contraction by 20cm3?

This is just the difference between the initial gas mixture (hydrocarbon and oxygen) and the final mixture (carbon dioxide and unreacted excess oxygen)
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