Question

A 150.0 mL gas tank contains 51.2 g of oxygen gas and 32.6 g helium gas. What is the total pressure in the tank? What is the partial pressure of oxygen?

Answer 1

no.of moles of O2 = (wt/molwt) = (51.2/32) = 1.6 moles

no.of moles of He = 32.6/4 = 8.2 moles

Total no.of moles = 1.6 + 8.2 = 9.8 moles

P_total = n_T *R*T/V

R = 0.0821

T = 25 +273 = 298 K

V =150 ml = 0.15 lt

P_total = (9.8)*0.0821*298/0.15 lt

P_total = 1598.4 atm.

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now calculate mole fractions

mole fraction of O2 = no. of moles of O2/Total no. of moles

                               = 1.6/9.8 = 0.16

mole fraction of He = 8.2/9.8 = 0.84

Partial pressure of O2 = molefraction of O2 * Total pressure

                               = 0.16* 1598.4 =255.7 atm.