Expert: Chris Larsen - 1/4/2011

Question
Hello Chris. I am doing a project for my English class where we were to interview a fifth grader and ask them a question which we have to answer in an essay. My question was, "If there is oxygen in water, why can't we breathe underwater?" So basically, my question is that since the molecule is H2O, why can't the oxygen be breathed in? I hope you can answer my question so I can give this little guy a good answer. If you do not know the answer, if there is anyone else that you could give me an e-mail address to that you think would know it would be very appreciated. Thank you!!

Answer
Hi Mike,

Thanks for the question!

You are correct, the chemical formula for water is 2 atoms of Hydrogen and 1 atom of Oxygen.  The problem that arises with respect to your question is the fact that each atom of Hydrogen is covalently bound to the atom of Oxygen; this results in 1 molecule of water.  Despite the fact that water molecules are partly composed of Oxygen, the Oxygen is a component of the water molecule and humans are not able to breathe the resulting liquid.  Unfortunately, the Oxygen is of no use to humans in the form of water.

Additionally, human lungs don't have enough surface area to extract enough of the Oxygen from water in order to survive.  Thus, human lungs require Oxygen as a gas (O2) in order to breathe.

Hope this helps!

-Chris