What Is the Molecular Formula of the Hydrocarbon?

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Discussion Overview

The discussion revolves around determining the molecular formula of a hydrocarbon based on its combustion reaction with oxygen, involving calculations related to the volumes of reactants and products. The context is primarily homework-related, focusing on chemical equations and stoichiometry.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a combustion equation involving a hydrocarbon and suggests using the greatest common divisor (GCD) for coefficients, but expresses difficulty in progressing further.
  • Another participant challenges the initial approach, stating that the use of GCD is incorrect due to unbalanced elements in the equation and suggests a different method involving variables to create a linear equation.
  • A third participant encourages the first poster to calculate the amounts of carbon and hydrogen based on the products of combustion, proposing a simplified equation without prefixes.
  • A fourth participant provides a specific equation format that aligns with a recognized specification, indicating a potential correct approach to the problem.

Areas of Agreement / Disagreement

Participants express differing views on the initial approach to the problem, with some agreeing on the need for a balanced equation while others dispute the method used. The discussion remains unresolved regarding the correct formulation of the combustion equation.

Contextual Notes

Participants have not fully resolved the assumptions regarding the stoichiometric coefficients and the balancing of the combustion reaction. The discussion reflects varying interpretations of how to approach the problem mathematically.

Who May Find This Useful

This discussion may be useful for students studying chemistry, particularly those focusing on stoichiometry and combustion reactions in hydrocarbons.

Sam_
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Homework Statement



0.1 dm^3 of a gaseous hydrocarbon may require 0.45 dm^3 of oxygen for a complete combustion to give 300 cm^3 of Carbon dioxide. All volumes are measured in the same environment. Calculate the molecular formula of the hydrocarbon.

The Attempt at a Solution



i tried getting the gdc of 10, 30 and 45 =90. and the have like

9 CxHy + 2 O2 --> 3 CO2 + H2O

but I cannot go further than this. please help. Thanks.
 
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as for the formula you have taken.. i don't understand why you've taken the GCD, but it is fundamentally wrong as the oxygen is not balanced on both sides [and neither is carbon or hydrogen].

What you need is a equation which is prefixed and suffixed by variables on both the sides to get you a linear equation which you can then solve...
 
Can you think of a way to calculate the amount of carbon in CO2 and hydrogen in H2O? You have a good start here:
CxHy + O2 --> CO2 + H2O
I've removed the prefixes you had (the '9', '2' and '3'). Can you solve it in terms of 'x' and 'y'?
 
CxHy + (x+y/4)O2 --> xCO2 +y/2H2O

thats the correct answer from ccea spec for alevel chemistry =]
 

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