Question: At STP propane (C3H8) burns in oxygen to form 2.15L of carbon dioxide and water.
The question is in 4 parts. I just need the first:
a)What mass of oxygen is necessary for this reaction?
So far I've got 2.15 L x 1 mole /22.4 L
But when I try to do the mole ratio, I don't know what to do since the 2.15 L is of carbon dioxide and water.
C3H8 + 5O2 ==> 3CO2 + 4H2O
2.15/22.4 = mols CO2 + mols H2O combined = 0.096
0.096 mols combined gas x (5 mols O2/7 mols combined gas) = ?mols O2.
To find the mass of oxygen required for the reaction, you need to use stoichiometry and the balanced chemical equation to determine the mole ratio between propane and oxygen.
The stoichiometric ratio can be obtained from the balanced chemical equation for the combustion of propane:
C3H8 + 5O2 -> 3CO2 + 4H2O
From the balanced equation, you can see that for every 1 mole of propane (C3H8), you need 5 moles of oxygen (O2) to produce 3 moles of carbon dioxide (CO2) and 4 moles of water (H2O).
Given that you have calculated the volume of carbon dioxide and water formed as 2.15 L, you need to convert this volume to moles using the ideal gas law. The conversion factor you have used, which is 1 mole / 22.4 L, is correct.
Now, you know that the moles of carbon dioxide and water formed are equal to the moles of propane reacted (assuming complete combustion). You can calculate the moles of propane by using the moles-to-volume ratio you have already calculated:
Moles of propane (C3H8) = 2.15 L x (1 mole / 22.4 L)
Next, you can determine the moles of oxygen required using the stoichiometric ratio from the balanced equation. In this case, you need 5 moles of oxygen for every 1 mole of propane:
Moles of oxygen required = Moles of propane (C3H8) x (5 moles O2 / 1 mole C3H8)
Finally, to find the mass of oxygen required, you need to use the molar mass of oxygen, which is approximately 32 g/mol:
Mass of oxygen required = Moles of oxygen required x Molar mass of oxygen
By plugging in the values from your calculations, you should be able to determine the mass of oxygen necessary for the reaction.