A .326L container holds 0.146g of Ne and an unknown amount of Ar at 30C and the total pressure is 627 mmHg. Calculate the moles of Ar present?
(I have calculated temp 308K, pressure is 0.825 atm and moles of Ne are .007)
Chem - DrBob222, Wednesday, March 3, 2010 at 3:25pm
T is 303 and not 308 K which means you need to recalculate pressure and n for Ne.
Use PV = nRT
You can calculate moles Ne, plug that in for n, and plug in R, T, and V. Calculate pressure for Ne (I get something like 0.55 atm but I rounded here and there. That will be in atm so change to mm Hg. You know total pressure is 627 mm Hg, subtract pressure Ne to obtain pressure Ar, then plug that back into PV = nRT to calculate n for Ar. Remember to convert mmHg back to atm.
Dr. Bob,
I'm calculating moles of Ar to be 0.0038, however, when plugging this into the online homework program it's marking it as incorrect. Am I doing a step incorrectly or do you get a similar answer? Thanks!
I get a similar answer but not the same. I obtained 0.00358 moles Ar.
To calculate the moles of Ar present, you need to first calculate the partial pressure of Ne in the container.
1. Start by converting the temperature from Celsius to Kelvin:
T = 30°C + 273.15 = 303.15 K
2. Use the ideal gas law equation (PV = nRT) to calculate the moles of Ne:
P = 627 mmHg = 0.825 atm (assuming this conversion is correct)
V = 0.326 L
R = 0.0821 L·atm/(mol·K) (gas constant)
nNe = (PNe * V) / (R * T)
You mentioned that you have already calculated the moles of Ne to be 0.007, so double-check your calculations to ensure accuracy.
3. Now, to get the partial pressure of Ne, you need to convert the moles of Ne into pressure in atm:
PNe = nNe * R * T / V
4. Calculate the pressure of the Argon (PAr) by subtracting PNe from the total pressure:
PAr = Ptotal - PNe
5. Convert the pressure of Ar from atm to mmHg:
PAr_mmHg = PAr * 760 mmHg/atm
6. Finally, use the ideal gas law equation again to calculate the moles of Ar:
nAr = (PAr_mmHg * V) / (760 mmHg * R * T)
Plug in the values you have obtained and make sure to calculate correctly to determine the exact moles of Ar present. Remember to round your final answer appropriately based on significant figures.
If you have followed these steps correctly and are still getting a different answer, double-check your calculations or consider seeking assistance from your instructor or peers.