chemistry p22 help!!

[Amna]

Hi This question from October/November 2010 is something I just can't understand.

Q1:

Davy and Faraday deduced the formula of A by exploding it with an excess of oxygen and
analysing the products of combustion.
(b) Complete and balance the following equation for the complete combustion of a
hydrocarbon with the formula CxHy.
CxHy + (x +y/4)O2 ------> ................................ + ................................

(c) When 10 cm3 of A was mixed at room temperature with 50 cm3 of oxygen (an excess)
and exploded, 40 cm3 of gas remained after cooling the apparatus to room temperature
and pressure.
When this 40 cm3 of gas was shaken with an excess of aqueous potassium hydroxide,
KOH, 30 cm3 of gas still remained.
(i) What is the identity of the 30 cm3 of gas that remained at the end of the
experiment?

(ii) The combustion of A produced a gas that reacted with the KOH(aq).
What is the identity of this gas?

(iii) What volume of the gas you have identified in (ii) was produced by the combustion
of A?

(iv) What volume of oxygen was used up in the combustion of A?


Please Please Help me out with this question

okay here's what i think the answers can be:

the blanks in the equation: xCO2 + yH2O
the reason being that any hydrocarbon gives carbon dioxide and water after complete combustion... and the x and y are just balancing acts...

c)i) O2 or oxygen gas; reason being that oxygen is in excess, so it's left over at the end when CO2 is absorbed by KOH and the water vapor is liquefied (the thing is cooled and water is liquid at rtp)

ii) CO2; it's acidic gas, reacts with/is absorbed by any strong alkali.

iii)10 cm3; reason being that a total of 40 cm3 of gas was produced and then after the CO2 was taken care of by the KOH, the volume that remained was 30 cm3, so 40-30=10...

iv) 20cm3; reason being that in the beginning there was 50 cm3 9in question) and then 30 cm3 was left at the end (as explained in (i))

hope that helped

 

[ShudyShab]

Wow Thank You so much it really did help ,e make sense of the question xo

 

[filza94]

hmm thank u so much..

 

[Amna]

lol no prob how did the paper go, btw?

 

[filza94]

itx was good n easyyy i felt n urz???

 

[Amna]

it wasn't as good as expected, but it was easy... so i guess the thresholds will go up... and my grade will come down... :/

 

[Paarth06]

the blanks in the equation: xCO2 + y/2 H2O*

 

[AndrewJustin]

What grade are y'all in?