Identifying Hydrocarbon X: A Homework Challenge

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Discussion Overview

The discussion revolves around a homework problem involving the identification of a hydrocarbon based on its combustion products and physical properties. Participants explore the calculations needed to determine the molecular formula of the hydrocarbon X, including the use of the ideal gas law and stoichiometry.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents the problem stating that combustion of hydrocarbon X produces 0.66g of carbon dioxide and 0.27g of water, leading to an empirical formula of CH2.
  • Another participant questions the units used in the calculations, specifically regarding the volume of gas and the gas constant R.
  • Multiple participants engage in clarifying the correct volume of one mole of gas at standard temperature and pressure (STP), with conflicting values of 24000 m³ and 22400 m³ being discussed.
  • There is a correction regarding the conversion of liters to cubic meters, with emphasis on the need for accurate unit conversion in calculations.
  • A participant claims to have found the molecular formula as C3H6 after correcting their earlier mistakes in the calculations.

Areas of Agreement / Disagreement

Participants express disagreement regarding the correct volume of one mole of gas at STP, with no consensus reached on the correct value. There is also uncertainty about the appropriate units and conversions needed for the calculations.

Contextual Notes

Limitations include unresolved mathematical steps and dependencies on correct unit conversions. The discussion reflects varying levels of understanding and corrections made throughout the thread.

Who May Find This Useful

Students and individuals interested in chemistry, particularly those studying gas laws, stoichiometry, and hydrocarbon identification.

desmond iking
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Homework Statement



Combustion of hydrocarbon X in excess oxygen produces 0.66g of carbon dioxide, and 0.27 g of water. At room tempertaure and pressure , X is a gas with density 1.75gdm^-3 . What could the molecular of X be?
What is the ans ? i only managed to get the empirical formula is CH2 ...

Homework Equations

The Attempt at a Solution


i tried pV = nRT , but i still doesn't get the ans . (1.01x10^3)(24000)= (1.75/MRR)(8.31)(273+27), the ans i found is MRR= 1.79x10^-4..
But tha ans is C4H8
 
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24000 - units? R - units?
 
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Borek said:
24000 - units? R - units?
24000m^3 R = 8.3145 J/mol·K , which part i did wrongly?
 
What is the volume of 1 mole of gas at STP?
 
Borek said:
What is the volume of 1 mole of gas at STP?
24000m^3
 
No, please check.
 
Borek said:
No, please check.
22400m^3 ?
 
Stop guessing, CHECK. Google is your friend.
 
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Borek said:
Stop guessing, CHECK. Google is your friend.
Ya , I checked it. 22400m cube
 
  • #10
No, this is still wrong. You are simply not paying attention, as you are repeating the same trivial mistake over and over again.

I gave you an important hint in my very first post in this thread.
 
  • #11
Borek said:
No, this is still wrong. You are simply not paying attention, as you are repeating the same trivial mistake over and over again.

I gave you an important hint in my very first post in this thread.
22.4litre. Which is also equal to 22400m3
 
  • #12
desmond iking said:
22.4litre.

Yes.

Which is also equal to 22400m3

No.

1 liter is about 4 cups. 22400 m3 is a volume of a bulky ten floors building.
 
  • #13
So what is the correct one to be substituted into the equation to get the ans?
 
  • #14
As your R uses units based on meter, volume has to be expressed in cubic meters as well. You need to convert 22.4 liters to cubic meters, just correctly.

I am not going to tell you "plug xxxx value" as this way you won't understand why it works and why what you did didn't work.

What methods of converting between units you know?
 
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  • #15
Borek said:
24000 - units? R - units?
well , i found the ans. thanks for pointing out my error. i 'd been thinking of this question few days...OMG! (101x10^3)(22400X10^-6)= (1.75X24/MRR)(8.31)(273+27)
So MRR = 46 , which is C3H6 . tHANKS!
 

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