Question

A stack gas (before scrubbing, that is, before removing SO2) has the following composition by mass: 6% SO2, 22% O2, 72% N2. What are the mole fractions of each species in the stack gas?

Answer 1

Step-by-step explanation:

Assume you have 100 g of the stack gas. Calculate the mass of each species in this sample according their percentages.

mass of sulphur : 6% of 100 g = 6 g

mass of oxygen : 22% of 100 g = 22 g

mass of nitrogen : 72% of 100 g = 72 g

Now calculate the number of moles of each species

number of moles of sulphur :
`(6g)/(64.066g/mol) = 0.09365 mol`

number of moles of oxygen:
`(22g)/(31.998g/mol) =0.6875 mol`

number of moles of nitrogen:
`(72g)/(28.0134g/mol) =2.570 mol`

Now to calculate the mol fraction of each we use the formula:

mol fraction of A =
`(number of moels of A)/(total number of moles available)`

Therefore

mole fraction of sulphur =
`(0.09365mol)/(3.35115 mol) =  0.028`

mole fraction of oxygen =
`(0.6875mol)/(3.35115 mol) =  0.205`

mole fraction of nitrogen =
`(2.570mol)/(3.35115 mol) =  0.767`