A gas sample containing only SO2, PF3 and SF6 has the following mass percent composition: 30.4% SO2 and 28.4% PF3. Calculate the partial pressure (atm) of SO2 if the total pressure of the sample is 676.4 torr.
I tried taking the total pressure in atm and multiplying it with the percent SO2 given, and came up with 0.271atm; however, the homework program that I'm using said that the correct answer is 0.391atm. Can someone point me in the right direction with this question?
partial pressure is on the basis of mole composition, not mass.
Right?
Yes it is based on mole composition, not mass. But how do you figure out the moles?
30.4% SO2 = mole fraction 0.304.
Atm total pressure = 676.4/760 = ??
mole fraction SO2 x total P (in atm) = partial pressure SO2.
mole fraction SO2 = 0.304.
I get the same answer as before = 0.271atm
According to the program, the right answer is 0.391atm
Luc, I apologize for sending you astray. Here is the way you do it. I tried a shortcut that isn't legal. :-0
You want to find the mole fraction of SO2, then
XSO2 * (676.4/760) = partial pressure SO2.
Take a 100 gram sample. That will give you
30.4 g SO2.
28.4 g PF3.
100 - (30.4 + 28.4) = xxg SF6.
Now convert all to moles.
30.4/molar mass SO2 = moles SO2.
28.4/molar mass PF3 = moles PF3.
xx g SF6 molar mass SF6 = moles SF6.
Add total moles.
mole fraction SO2 = (moles SO2/total moles). Then use the above (X*total P = partial pressure SO2.
This will give you 0.391 atm.
To calculate the partial pressure of SO2 in the gas sample, we need to understand the concept of mole fraction and how it relates to partial pressure.
Mole fraction (X) is the ratio of the number of moles of a component to the total number of moles in a mixture. In this case, we need to find the mole fraction of SO2 in the gas sample.
First, let's convert the mass percentages of SO2 and PF3 to moles, assuming we have a 100 g sample of the gas:
1. Calculate the number of moles of SO2:
Mass of SO2 = 30.4% of 100 g = 30.4 g
Molar mass of SO2 = 64.06 g/mol (sulfur dioxide)
Moles of SO2 = Mass of SO2 / Molar mass of SO2
2. Calculate the number of moles of PF3:
Mass of PF3 = 28.4% of 100 g = 28.4 g
Molar mass of PF3 = 87.97 g/mol (phosphorus trifluoride)
Moles of PF3 = Mass of PF3 / Molar mass of PF3
Now, we can calculate the total moles of the gas sample by summing up the moles of SO2 and PF3.
Total moles = Moles of SO2 + Moles of PF3
To find the mole fraction of SO2, divide the moles of SO2 by the total moles of the gas sample:
Mole fraction of SO2 = Moles of SO2 / Total moles
Next, we can use the ideal gas law to find the partial pressure of SO2. The ideal gas law equation is:
PV = nRT
where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature.
In this case, the total pressure of the gas sample is given as 676.4 torr. We need to convert it to atm by dividing by 760 (since 1 atm = 760 torr).
Partial pressure of SO2 = Mole fraction of SO2 * Total pressure in atm
Multiply the mole fraction of SO2 by the total pressure to find the partial pressure of SO2 in atm.
Finally, convert the partial pressure from atm to torr if needed.
I can perform the calculations for you, but I need the molar masses of PF3 and SF6 to complete the calculations.