Here is a question sent in via email by an avid student reader of this chemistry blogsite.
Hope to see some suggested answers below and the reasoning/explanation to it.
PS: Remember – Do not be afraid of making mistakes now. I rather you make mistakes now then during your examinations.
Question 1:
20cm3 of a gaseous hydrocarbon was mixed with 100cm3 of oxygen and the mixture sparked so that the hydrocarbon was completely burnt. The volume of gas remaining at the end of the combustion was 70cm3. After passing over soda lime, this volume was reduced to 10cm3. All gases were measured at 25C and at the same pressure.
(a) What volume of oxygen gas remained unburnt at the end?
(b) What volume of oxygen gas was used in the combustion?
(c) What volume of carbon dioxide was produced in the combustion?
(d) Deduce the formula of hydrocarbon.
equa: CxHy +(x+y/4)O2 ?? xCO2 + y/2H2O
(a)…..10cm3 (left after passing soda lime)
(b)…..90cm3(initial volume -unburnt volume)
(c)…..60cm3(70-10) absorbed by soda lime
(d)…..C3H6.(first find x by using the equation above nd the volumes(CxHy and CO2)then y by O2 nd CO2.get 3 for x nd 6 for y.
Something i dont understand. In the resulting 70 cm3 mixture, there will be excess oxygen, carbon dioxide formed and water vapour as well… We can say that of thse 70cm3, 60cm3 are carbon dioxide but how can we say that the remaining 10cm3 are oxygen only??? Please clear my doubts…
plz told me is it correct is it calcium
Which atom loses two electrons from its valence shell to form an ion?
a)calcium
b)carbon
c)chlorine
d)oxygen
very good attempt. i agree with answers to a, b and c.
Could you explain how you get your answers of CH4 in part (d)?
very good attempt. i agree with answers to a, b and c. check out the answer to (d) in other’s response
very good attempt. i agree with answers to a, b and c.
Could you explain how you get your answers of C3H6 in part (d)?
keep learning, whenever in doubt quickly ask your chemistry teacher in school.
wish you the best
there is no requirement to know the details of water in this question.
Hydrocarbon (limiting reactant) + Oxygen (excess reactant) –> Carbon Dioxide + Water + Excess Unreacted Oxygen Gas
Think about it using the word equation above.
water will be obviously, otherwise how are u going to calculate hydrogen coefficient???
I agree with Yimu’s answers
(a)10 cm3
(b)90 cm3
(c)60 cm3
(d)C3H6
Could you tell me if my answers are goo?
When a hydrocarbon is completely burnt the products will be carbon dioxide and water and unreacted oxygen (in this case)
Nothing is mentioned about water or steam in the question.
Could you please explain.
Thanks.
Rajagopal
a) 10……….coz it is mentioned after soda lime was introduced 10 cm was left
b) 90…………simply 100-10=90
c) 60…………10 was oxygen rest 60 removed by soda lime and 10+60=70 that was given as the total left over
d) sorry……………im not certain about this one so i request to please tell me about my this work and any correction that need to be made.
i don’t understand it.Sean explain it in detail……
Thank you for your contribution for helping chemistry students all over the world.
With you,i am very optimistic of becoming a great chemist.In my school,i don’t have
a good chemistry teacher but now,am confident to learn more from you.Thanks.
10cm3 of oxygen was left over
30cm3 of the gas was used for combustion
90cm3 of carbondioxide was formed
ch4 that is methane
tell me if my answer is right and for which class is this question coz i am in class 10