Chemistry combustion analysis gas problem

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Discussion Overview

The discussion revolves around a homework problem involving the combustion analysis of a hydrocarbon, specifically determining its molecular and empirical formulas based on the products of combustion. The scope includes mathematical reasoning and chemical analysis.

Discussion Character

  • Homework-related, Mathematical reasoning

Main Points Raised

  • The original poster (OP) calculates the moles of CO2 and H2O produced from the combustion of a hydrocarbon and proposes a molecular formula of C5H6 based on their calculations.
  • Some participants suggest that the molecular formula could also be C10H12 or C15H18, indicating multiple possibilities based on the data provided.
  • The OP expresses uncertainty about whether their calculated molecular formula is correct and questions the validity of rounding the ratio to arrive at a different formula.
  • There is a mention of confusion regarding the attribution of replies, with one participant mistakenly addressing another's comment.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the molecular formula, as multiple competing views are presented regarding the possible formulas derived from the combustion analysis.

Contextual Notes

The discussion includes unresolved mathematical steps and assumptions regarding the ratios of moles, as well as the potential for different molecular formulas based on the same combustion data.

Nellen2222
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Homework Statement



Complete combustion of a 0.0150 mol sample of a hydrocarbon, CxHy, gives 1.680L of CO2 at STP and 0.810g of H2O
a) what is the molecular formula
b) what is empirical formula

Homework Equations



pv=nRt

The Attempt at a Solution



a) mol of co2: n=pv/Rt=1 atm * 1.680L/0.0821*273= 0.074955495mol

- Mol of h2o: 0.810g/18.02g/mol * 2 = 0.08990011 mol H2

mol ratio: 0.08990011/0.074955495= 1.199379845... * 5 = 6

molecular formula: c5h6.

Is this wrong? is it possible to multiply by four and round the number to 5 instead of 6? so that it would be c4h5? Or is the above one correct?also: how do i get the molecular formula? i can't get a lowest whole number ratio here.
Thanks!
 
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Looks good to me provided you did the math correctly. Could also be C10H12 or C15H18...
 
Last edited:
Nellen2222 said:
0.0150 mol sample of a hydrocarbon

chemisttree said:
Could also be C10H12 or C15H18...

C5H6 it is, OP started with the number of moles.
 
Argh! That should have been Nellen's reply.
 
Oops.
 

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