Question

A mixture of nitrogen (N₂) and helium has a volume of 250mL at 30 degree C and a total pressure of 745mmHg. (8.5, 8.6, 8.7)

a. If the partial pressure of helium is 32mmHg, what is the partial pressure of the nitrogen?

b. What is the final volume in liters, of the nitrogen at STP?

Answer 1

a. By Dalton's Law, the total pressure is the sum of the partial pressures, so:

N2 + He= 745

N2 + 32 = 745

N2= 745 - 32= 713mmHg

b. Using the pressure we found now we will find the number of moles of nitrogen in the sample using the PV=nRT equation. (we have to use temperature in kelvin= 30°C=303°K) R=  62.36 mmHg.L/mol.K

PV=nRT

713x 0.250=n 62.36x 303

n= 713x 0.250/62.36x 303

n= 9.43x10^-3 moles

Now we will use the equation again, but this time using the moles and standard pressure (1 atm or 760 mm Hg) and temperature (273 K) to solve for volume.

PV=nRT

760xV=9.43x10^-3 x62.36x273

V=9.43x10^-3 x62.36x273/760

V= 0.211 L or 211.31 mL