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In a eudiometer $\pu{14 ml}$ of $\ce{CH4}$ and $\pu{38.5 ml}$ of $\ce{O2}$ was introduced. After explosion and cooling to initial temperature ($\pu{23°C}$) the volume of eudiometer was found to be $\pu{25 ml}$. Calculate the vapour pressure(in $\pu{mm Hg}$) of aqueous solution containing a non-volatile solute (A) at $\pu{23 °C}$. Mole fraction of (A) is $0.1$. The pressure of eudiometer is $\pu{1 atm}$ and is constant.

I wrote the balanced equation. Then applied Avogradro's law and found that the volume of gases in the eudiometer after reaction is $\pu{24.5ml}$. So the extra $\pu{0.5ml}$ must be due to some water which must have converted into gas. Using $PV=nRT$ I can calculate the no. of moles of water evaporated, but I am unable to understand the last part of the question regarding solute A. Is there some information missing in the question regarding solute A? (I assumed it as the final solution after the reaction, but still don't know how to proceed).

Answer is 13.68.

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  • $\begingroup$ The vapour pressure of the solution is equal to the partial pressure of water in the gas phase. I'm not sure how this question was intended. You could get the vapour pressure of water at the given temperature from published data (pure water: 21.1 torr), or you could figure out the partial pressure of water in the solution. A complicating factor is that CO2 is soluble in water - maybe you are supposed to ignore that. If the non-volatile solute makes the solution acidic, not much CO2 will dissolve, but if it is basic, a lot will dissolve. $\endgroup$ – Karsten Theis Jun 11 at 17:36
  • $\begingroup$ Could you edit your question to show your work that led to 24.5 mL of product? Are you including water in that, or is that just CO2? $\endgroup$ – Karsten Theis Jun 11 at 17:37
  • $\begingroup$ "The pressure of the eudiometer is 1 atm and is constant." "After explosion..." :/ $\endgroup$ – Zhe Jun 11 at 19:40
  • $\begingroup$ @Karsten Theis. The 24.5ml I have accounted is the volume for the excess O2+ volume of CO2 formed. $\endgroup$ – thewitness Jun 12 at 10:01
  • $\begingroup$ 0.5 / 25•760*0.9=13.68, but this is not chemistry. $\endgroup$ – Karsten Theis Jun 12 at 10:52

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