A heliox tank contains 32% helium and 68% oxygen. the total pressure in the tank is 395 kPa. What is the partial pressure of oxygen in the tank?

Pp O2 = 82.944 KPa

Explanation:

heliox tank:

∴ %wt He = 32%

∴ %wt O2 = 68%

∴ Pt = 395 KPa

⇒ Pp O2 = ?

assuming a mix of ideal gases at the temperature and volumen of the mix:

∴ Pi = RTni/V

∴ Pt = RTnt/V

⇒ Pi/Pt = ni/nt = Xi

⇒ Pi = (Xi)*(Pt)

∴ Xi: molar fraction (ni/nt)

⇒ 0.68 = mass O2/mass mix

assuming mass mix = 100 g

⇒ mass O2 = 68 g

∴ molar mass O2 = 32 g/mol

⇒ moles O2 = (68 g)(mol/32 g) = 2.125 mol O2

⇒ mass He = 32 g

∴ molar mass He = 4.0026 g/mol

⇒ moles He = (32 g)(mol/4.0026 g) = 7.995 mol He

⇒ nt = nO2 + nHe = 2.125 mol + 7.995 mol = 10.12 moles

molar fraction O2:

⇒ X O2 = nO2/nt = (2.125 mol/10.12 mol) = 0.2099

⇒ Pp O2 = (X O2)(Pt)

⇒ Pp O2 = (0.2099)(395 KPa)

⇒ Pp O2 = 82.944 KPa

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