Question

A sample of natural gas contains 8.24 moles of methane, 0.421 moles of ethane, and 0.116 moles of propane. If the total pressure of the gases is 1.23 x 10³ mm Hg, what is the partial pressure of ethane? (Show your check)

a.1.29 atm

b.0.0656 atm

c.0.0214 atm

d.1.52 atm

e.0.0776 atm

Answer 1

Answer – We are given the moles of methane = 8.24 moles, moles of ethane = 0.421 moles

Moles of propane = 0.116 moles

Total pressure = 1.23 x 10³ mm Hg

We need to first calculate mole fraction of ethane

Total moles = 8.24+0.421+0.116 = 8.777 moles

We know formula

Mole fraction = mole / total moles

Mole fraction of ethane = 0.421 moles / 8.777 moles

                                      = 0.0480

Now we need to convert the given total pressure mm Hg to atm

We know

760 mm Hg = 1 atm

So, 1.23 x 10³ mm Hg = ?

= 1.62 atm

We know the relationship between partial pressure and total pressure that is Dalton’s law –

Mole fraction = partial pressure / total pressure

So, partial pressure of ethane = mole fraction of ethane * total pressure

                                                = 0.0480 * 1.62 atm

                                                = 0.0776 atm

So the correct answer is e) 0.0776 atm