[salam]

Hello, this question has been giving me a lot of trouble for quite some time.

I will just outline the details of the question here:

You have a 10 L sample of an unknown gas at STP which undergoes combustion in the presence of excess oxygen. The products were then isolated and cooled at STP. The products were Carbon Dioxide (20 L of gas) and Water (16 g of liquid). What is the molecular formula?

Now from my research, there are many similar examples like this, but they provide the mass of the unknown sample, whereas here, you have the volume. I'm thinking of trying to convert this volume to mass, and then dividing it by the moles you get from n = PV / RT to get molar mass.  And then from there, somehow using it to get to the molecular formula.

Can someone please guide me in the right direction on this.

[docnet]

From the given information of 20 L of Carbon Dioxide you can go straight to finding the moles, given conditions are STP. Use the proper gas constant so that the units cancel out and find the moles of C and use the other given information (H₂0) to find the moles of Hydrogen atoms in the original sample.

[AWK]

There is an error in your data. Should be 18 g of water.

[Vidya]

Hello, this question has been giving me a lot of trouble for quite some time.

I will just outline the details of the question here:

You have a 10 L sample of an unknown gas at STP which undergoes combustion in the presence of excess oxygen. The products were then isolated and cooled at STP. The products were Carbon Dioxide (20 L of gas) and Water (16 g of liquid). What is the molecular formula?

Now from my research, there are many similar examples like this, but they provide the mass of the unknown sample, whereas here, you have the volume. I'm thinking of trying to convert this volume to mass, and then dividing it by the moles you get from n = PV / RT to get molar mass.  And then from there, somehow using it to get to the molecular formula.

Can someone please guide me in the right direction on this.

Convert L of CO2 ---> moles of CO2 at STP---> moles of C
g H2O ---> moles of H2O -----> moles of H
These are the moles of C and H present in 10L of the sample
convert 10L of sample in moles of the sample
moles of C / moles of the sample will give you moles C in one mole of the sample
similarly you can work out moles of H in each mole of the sample

I am sure you know that at STP 22.4L of any gas = 1 mole of the gas 

[DrCMS]

There is an error in your data. Should be 18 g of water.

No I think 16g H₂O is probably correct to match with 20L of CO₂

[docnet]

To the op: remember, there are actually 2 moles of H in each mole of H₂O 

[AWK]

There is an error in your data. Should be 18 g of water.

No I think 16g H₂O is probably correct to match with 20L of CO₂

My fault!

Quote from: Vidya on Today at 08:03:48

Can someone please guide me in the right direction on this.
Convert L of CO2 ---> moles of CO2 at STP---> moles of C
g H2O ---> moles of H2O -----> moles of H
These are the moles of C and H present in 10L of the sample
convert 10L of sample in moles of the sample
moles of C / moles of the sample will give you moles C in one mole of the sample
similarly you can work out moles of H in each mole of the sample

There is no need for conversion, as above
The Avogadro law says:
"volumi uguali di gas diversi, alla stessa temperatura e pressione, contengono lo stesso numero di molecole"
From this law you easily can calculate number of carbon atoms (without calculator).
Converting mass of water to its volume at STP (even this can be done without calculator) you can easily obtain number of molecules of water (hence hydrogen atoms).
Note: 16 g of water gives you about 0.6 % error, now not accepted as a result of elemental analysis for H.

[salam]

Hello, this question has been giving me a lot of trouble for quite some time.

I will just outline the details of the question here:

You have a 10 L sample of an unknown gas at STP which undergoes combustion in the presence of excess oxygen. The products were then isolated and cooled at STP. The products were Carbon Dioxide (20 L of gas) and Water (16 g of liquid). What is the molecular formula?

Now from my research, there are many similar examples like this, but they provide the mass of the unknown sample, whereas here, you have the volume. I'm thinking of trying to convert this volume to mass, and then dividing it by the moles you get from n = PV / RT to get molar mass.  And then from there, somehow using it to get to the molecular formula.

Can someone please guide me in the right direction on this.

Convert L of CO2 ---> moles of CO2 at STP---> moles of C
g H2O ---> moles of H2O -----> moles of H
These are the moles of C and H present in 10L of the sample
convert 10L of sample in moles of the sample
moles of C / moles of the sample will give you moles C in one mole of the sample
similarly you can work out moles of H in each mole of the sample

I am sure you know that at STP 22.4L of any gas = 1 mole of the gas

Thank you so much, you helped me get the answer and I understand the methodology. Many thanks!

And thanks to everyone else too who also helped me with this question!