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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: --whiteskies on February 21, 2014, 11:32:33 am

Title: --whiteskies' Chemistry Thread
Post by: --whiteskies on February 21, 2014, 11:32:33 am

Please help and thank you so much!

Complete combustion of a 0.0100mol sample of a hydrocarbon gives 1.792L of CO₂ at STP and 1.261_g of H₂0.
a) What is the MF of the hydrocarbon?
b) What is the EF of the hydrocarbon?

I know the theory behind this question and how to work out the empirical formula in general, but I'm getting a weird mole ratio that doesn't seem right.

Title: Re: --whiteskies' Chemistry Thread
Post by: swagsxcboi on February 21, 2014, 09:34:54 pm

strange.. I'm getting C₂H₆₃ or something like that.
perhaps i'm completely wrong. lol

EDIT: completely screwed up
let me try again.
For CO₂
PV=nRT  V=1.792L R=8.31  At STP  P= 101.3 kPa  T= 273K
101.3 x 1.792 = n x 8.31 x 273
n(CO₂)= 0.08001 mols
n(CO2) = n(C) from hydrocarbon
n(C) = 0.08001 mols

For H₂O
1.261g of H₂O
n=m/M
n= 1.261/18
n(H₂O) = 0.07005 mols
n(H₂O) x 2 = n(H)
n(H)= 0.1401111 mols

0.1401111/0.080017279 = 1.75
For every C there will be 1.75 H  x 4 to get lowest whole number mol ratio
C₄H₇


 

Title: Re: --whiteskies' Chemistry Thread
Post by: RKTR on February 21, 2014, 11:22:49 pm

Is it C8H14 and C4H7?

Title: Re: --whiteskies' Chemistry Thread
Post by: Kuroyuki on February 21, 2014, 11:24:03 pm

Quote from: RKTR on February 21, 2014, 11:22:49 pm

Is it C8H14 and C4H7?

I got the C4H7 aswell.

Title: Re: --whiteskies' Chemistry Thread
Post by: --whiteskies on February 23, 2014, 11:04:49 pm

Quote from: swagsxcboi on February 21, 2014, 09:34:54 pm

strange.. I'm getting C₂H₆₃ or something like that.
perhaps i'm completely wrong. lol

EDIT: completely screwed up
let me try again.
For CO₂
PV=nRT  V=1.792L R=8.31  At STP  P= 101.3 kPa  T= 273K
101.3 x 1.792 = n x 8.31 x 273
n(CO₂)= 0.08001 mols
n(CO2) = n(C) from hydrocarbon
n(C) = 0.08001 mols

For H₂O
1.261g of H₂O
n=m/M
n= 1.261/18
n(H₂O) = 0.07005 mols
n(H₂O) x 2 = n(H)
n(H)= 0.1401111 mols

0.1401111/0.080017279 = 1.75
For every C there will be 1.75 H  x 4 to get lowest whole number mol ratio
C₄H₇

Quote from: RKTR on February 21, 2014, 11:22:49 pm

Is it C8H14 and C4H7?

Quote from: Kuroyuki on February 21, 2014, 11:24:03 pm

I got the C4H7 aswell.

yes guys yes it is and thank you so so much :)