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

Watch
Stormragexox
Badges: 10
Rep:
?
#1
Report Thread starter 1 year ago
#1
Hey everyone i am stuck with a question i found out what x is but i don't know what to do nect
0
reply
charco
Badges: 17
Rep:
?
#2
Report 1 year ago
#2
(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 ...
0
reply
Stormragexox
Badges: 10
Rep:
?
#3
Report Thread starter 1 year ago
#3
(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
Name:  IMG_0436 (1).jpg
Views: 56
Size:  111.9 KB
0
reply
Stormragexox
Badges: 10
Rep:
?
#4
Report Thread starter 1 year ago
#4
(Original post by charco)
Find y ...
(Original post by Stormragexox)
Name:  IMG_0436 (1).jpg
Views: 56
Size:  111.9 KB
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?
Last edited by Stormragexox; 1 year ago
0
reply
charco
Badges: 17
Rep:
?
#5
Report 1 year ago
#5
(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
Last edited by charco; 1 year ago
1
reply
Stormragexox
Badges: 10
Rep:
?
#6
Report Thread starter 1 year ago
#6
(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
0
reply
charco
Badges: 17
Rep:
?
#7
Report 1 year ago
#7
(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)
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

How are you finding researching unis for 2021 entry?

I have been able to get all the information I need from online research (51)
19.39%
I have tried virtual events and found them useful (58)
22.05%
I have tried virtual events and did not find them useful (50)
19.01%
I would be interested in trying socially distanced or scaled down in person events (55)
20.91%
I want to but don't know where to start with researching unis for 2021 entry (25)
9.51%
I haven't started researching yet (24)
9.13%

Watched Threads

View All
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise