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

Answer:

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 : $\frac{6g}{64.066g/mol} = 0.09365 mol$

number of moles of oxygen: $\frac{22g}{31.998g/mol} =0.6875 mol$

number of moles of nitrogen: $\frac{72g}{28.0134g/mol} =2.570 mol$

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

mol fraction of A = $\frac{number of moels of A}{total number of moles available}$

Therefore

mole fraction of sulphur = $\frac{0.09365mol}{3.35115 mol} =  0.028$

mole fraction of oxygen = $\frac{0.6875mol}{3.35115 mol} =  0.205$

mole fraction of nitrogen = $\frac{2.570mol}{3.35115 mol} =  0.767$