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### Course: MCAT>Unit 7

Lesson 11: Respiratory system

# O2 and CO2 solubility

Get an intuition for why carbon dioxide is so much more soluble than oxygen when it goes into water. Rishi is a pediatric infectious disease physician and works at Khan Academy. These videos do not provide medical advice and are for informational purposes only. The videos are not intended to be a substitute for professional medical advice, diagnosis or treatment. Always seek the advice of a qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read or seen in any Khan Academy video. Created by Rishi Desai.

## Want to join the conversation?

• I know you are meant to divide partial pressure by concentration to get Kh but how exactly did you get 769 at and 29 at ? I seem to be getting a different answer
• I think the main problem has to do with the units. Concentration is given in mmol/l (that is mol x 10-3) and Kh units are in mol. So if we take that into account you should get 777 for Oxygen and 29 for carbon dioxide. The disparity between 769 and 777 can be accounted for if we assume that the concentration value that was used had some extra digits (e.g. 0.2731 mmol/L). So the values for the equation for Oxygen would be 0.21 atm / 0.0002731 mol/L.
• How about the concentration of nitrogen in our blood?
• Nitrogen (N2) is an extremely stable molecule due to it's triple bond. Due to it's stability the molecules on Nitrogen that diffuse through the blood do not undergo many, if any, chemical reactions in the blood.

To answer your questions, the amount of Nitrogen we inspire and expire is approximately 79%, due to the reason state above.

• Doesn't there need to be carbonic anhydrase to catalyze the reaction of CO2 and H2O into H2CO3
• Yes, but it only speeds up the reaction, nothing else.
• The difference in the ratios of CO2 solubility to O2 solubility between room temperature and body temperature- is that more due to CO2 becoming less soluble at warmer temps, or O2 becoming more soluble?
And if you have hypothermia, is the increase in CO2 solubility or decrease in O2 solubility pronounced enough to lead to acidosis or hypoxia, respectively? Does that contribute at all to death from hypothermia?
• In regards to your first question, gasses will generally become less soluble at higher temperatures because they will have more kinetic energy which allows them to bounce around in a gaseous form.
I would assume that the solubility of both CO2 and O2 would decrease at higher temps. but less so CO2 because much of the CO2 molecules will have already converted into bicarb and H+.
• at Henry's law is written as Pressure over concentration= kH. However i learned that concentration over pressure =kH which formula is correct?
• The way you learned it and the way it is presented are really two sides of the same coin. It all comes down to how you want to express the answer. You can rearrange the formula in many different ways depending on the situation and how you want to express the units.

In your learning of Henry's law the units were expressed in mols(gas) / L(solution)*atm whereas in the video the units are expressed in L(solution)*atm / mol(gas).

This is why it is very important to express your units and check when you use a constant that you are in the correct units to use it. I have made this mistake many times in undergrad.

source: https://chemengineering.wikispaces.com/Henry%27s+Law
• At , I start to get really lost, Could someone please explain to me how Rishi came up with the number 769 and the term after it? Thanks!
• What is concentration and nitrogen in our blood
• The amount of Nitrogen we inspire and expire is approximately 79% because it is a stable molecule (due to triple bond) and so does'nt participate much in chemical reactions.
• If Carbon Dioxide is more soluble in blood then Oxygen, why does Oxygen go into the blood vessels, and Carbon Dioxide leaves during respiration.