Divers often use nitrox, a mix of oxygen and nitrogen with more oxygen than air…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Divers often use nitrox, a mix of oxygen and nitrogen with more oxygen than air. A diver's mix is oxygen by moles. The partial pressure of oxygen must stay below kPa. At the surface the pressure is kPa, and it grows by kPa for each metre of sea water. What is the deepest safe depth? What is it for ordinary air, with oxygen?
Need a reminder? The key ideaShow
Each gas in a mixture fills the whole volume. Its partial pressure is . The total pressure is the sum:
A real gas has below when the pull between molecules wins and above when their size wins.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The total pressure at the limit. kPa.
Step 2. The depth. The water adds kPa. At kPa a metre that is m.
Step 3. Ordinary air. kPa, so the depth is m.
Answer: m with nitrox, and m with air.
Check. More oxygen in the mix reaches the oxygen limit at a smaller total pressure, so the safe depth is smaller. It makes sense.
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