Calculating Total Pressure

Question

A 10.0L tank at 25.8°C is filled with 13.8g of dinitrogen monoxide gas and 10.6g of sulfur hexafluoride gas. You can assume both gases behave as ideal gases under these conditions.

Calculate the total pressure in the tank. Round your answer to the correct number of significant digits.

Answer 1

Ideal gas law: PV = nRT

P = pressure = ? atm

V = volume in liters = 10.0 L

n = moles of gas = moles of N2O + moles SF6 (see below)

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 25.8 + 273 = 298.8K

moles N2O = 13.8 g N2O x 1 mol/44.01 g = 0.3136 moles

moles SF6 =10.6 g SF6 x 1 mol/146.1 g = 0.07255 moles

Total moles of gas = 0.3136 + 0.07255 = 0.3862 moles

Solving ideal gas law for P, we have...

P = nRT/V

P = (0.3862)(0.0821)(298.8) / 10.0

P = 0.947 atm (3 sig. figs.)

Answer 2

So Carsyn E.,

Use the Universal Gas Law with your given data, and calculate the MW of N2O and SF6 from Periodic Table, in order to get partial pressures of each gas, then sum those.

As long as you don't inhale any of it, it's no laughing matter, the calculation. (N2O is "laughing gas" used for mild anaesthesia).

For significant digits, carry all the calculator precision you can (say, 5 figures) through the calculation, then round to 3 on final pressure. It's not like significant figures are what scientists use in practice, but it's a start. True scientists use propagation of indeterminate errors, which you can't here, since you don't have data on those, so you assume precision at the stated data level.

-- Cheers, --Mr. d.