Suggested Response - Q6

**Atmospheric air is supplied to a yeast propagation vessel to provide oxygen for yeast growth. The vessel is kept under a slight back-pressure of 1.1 bar a. What will be the partial pressure of oxygen once the air has filled the vessel? You may assume the oxygen content of atmospheric air to be 21% (v/v).

If pure oxygen was supplied to the propagation vessel at the same pressure, what would be the partial pressure of oxygen?

Response:

We can express Dalton’s law as the following:

P subscript T space end subscript equals space p subscript N subscript 2 end subscript space plus space p subscript O subscript 2 end subscript space plus space p subscript A r space end subscript plus space p subscript C O subscript 2 end subscript plus space p subscript o t h e r s end subscript

The partial pressure of any component, in this case, oxygen, is given by:

p subscript O subscript 2 end subscript space equals space P subscript T x subscript O subscript 2 end subscript

The oxygen molar fraction x subscript O subscript 2 end subscript is equal to the volume fraction of 0.21 (21%), so the partial pressure of oxygen is given by:

p subscript O subscript 2 end subscript space equals space P subscript T x subscript O subscript 2 end subscript space equals space 1.1 space cross times space 10 to the power of 5 space cross times space 0.21 space equals space 23.1 space k P a space a

If pure oxygen was used instead of air, which is a mixture of gases, then the partial pressure of oxygen would be equal to the total gas pressure of 1.1 bar a. If you are still unsure, consider that the molar and volumetric fraction of oxygen would be 1 and introduce this into the partial pressure expression:

p subscript O subscript 2 end subscript space equals space P subscript T x subscript O subscript 2 end subscript space equals space P subscript T space cross times space 1.0 space equals space P subscript T space equals space 1.1 space b a r space a

You have completed 0% of the lesson
0%