Things I don't understand...

Well, I've never been shy about displaying my ignorance about things. Helps me learn something I didn't know before, I guess.

Anyway....

What are dead zones simple definition?

Dead zones are low-oxygen, or hypoxic, areas in the world's oceans and lakes. Because most organisms need oxygen to live, few organisms can survive in hypoxic conditions. That is why these areas are called dead zones.

OK, so what is water? H2O, right? Two atoms of hydrogen and one atom of oxygen. So if oxygen gets depleted from water, doesn't that just leave the H2 behind? Hydrogen is a gas. So why doesn't the area of zero oxygen atoms ,and ONLY hydrogen atoms, just float away into the atmosphere? And the hole left behind by the exiting hydrogen gas get filled in with proper water molecules?

And while I am at it, how in the world do you get a liquid by combining three atoms of two gaseous elements? If you combine nitrogen with oxygen what do you get? Well, another gas this time, like you would expect. Of course, if nitrogen and oxygen would combine easily and naturally in the atmosphere, I guess the world would be a much different place with everyone breathing nitrous oxide (laughing gas).

Not sure you want a serious answer, but here's a high school chemistry explanation:

Hydrogen and oxygen combine to make water, and when they do they become chemically bonded. Chemical bonds happen because:

(a) atoms (the smallest bit of any element) are a positively charged nucleus (made of protons and usually neutrons) orbited by electrons;
(b) the electrons orbit the nucleus in 'shells' -- layers around the nucleus -- and each shell can contain a certain number of electrons (shell 1 holds 2 electrons, shell 2 holds 8, shell 3 holds 18, etc)
(c) shells with room for another electron attract electrons from other atoms of the same or different elements

So oxygen has eight electrons (2 in the first shell and 6 in the second), and so "wants" to pick up two more. Each hydrogen atom has one electron, so oxygen bonds to two hydrogens and is stable in that configuration, and it takes energy to separate them, as through electrolysis.

That energy can be released by combining hydrogen and oxygen, as in rocket engines, and the Hindenburg.

Oxygen that is dissolved in water is just dissolved in water. There is water, and then in between the water molecules there are oxygen (O2) molecules. The water is chemically stable, and so doesn't chemically bond to the oxygen. Hypoxic water doesn't have enough dissolved oxygen in it to sustain life, and the oxygen that makes up the H2O is chemically bound and can't be used for breathing. Fish breathe dissolved oxygen, but have no way to separate out the O from the H in water. Submarines employ electrolysis to separate out the O and H from desalinated seawater so the crew can breathe the O.

There is actually some N2O in the atmosphere -- Wikipedia says 330 ppb and rising due to human emissions (preindustrial level was 270 ppb, presumably formed in the upper atmosphere like ozone). I just learned that it can be made by heating ammonium nitrate, which sounds like a good way to blow up your neighborhood.

Quantitative chemistry (that is, figuring out how elements work simply by knowing how many protons and electrons they have) is one of the most mind-blowing of scientific discoveries, as far as I'm concerned.

The oxygen found in water isn't available for use in respiration unless your a plant or some species of microbes, it is considered bound and a lot of energy is required to split it from the hydrogen atoms.

Well those two gases are only gases above a certain temperature and within a range of atmospheric pressures, outside of those conditions they are liquids or solids.. The same goes for water (assuming it's pure so no need to worry about freezing point depression or boiling point elevation), it's a liquid at 1 atmosphere and below 212 F, and begins to shift to a solid at 1 atmosphere of pressure and 32 F.

If you look at how the electrical charge is spread across the water molecule, you'll discover that it is a very polar molecule with a net positive and negative charge at opposite ends of the molecule. This charge causes the molecules to loosely bind together resulting in a liquid under the above conditions.

A simplified explanation...

Ed

Very interesting, all. So, what causes these dead zones? I remember when I had fish tanks I would only aerate one side of the tank, the circulating water would move in a way to homogenize the aerated water with the unaerated water and the fish never had problems. Aren't there all sorts of currents and tides that move ocean water around?

Originally Posted by Socratic Monologue

Oxygen that is dissolved in water is just dissolved in water. There is water, and then in between the water molecules there are oxygen (O2) molecules. The water is chemically stable, and so doesn't chemically bond to the oxygen.

Yeah, kind of a serious question, to stimulate some discussion about just "things".

So that *free* oxygen that is not bound to hydrogen to form water is dissolved into what, exactly? What is it bound to that keeps it from just rising to the top of all the water and then exiting into the atmosphere?

And to keep this percolating, I was going to pose the question of where does the salt come from in the oceans, but that drills down to the question of where did the chlorine come from that makes salt? Whenever I look up where chlorine comes from, the answer is that it comes from salt. So this sort of sets up a "what came first, the chicken or the egg" sort of question.

Originally Posted by WebSlave

So that *free* oxygen that is not bound to hydrogen to form water is dissolved into what, exactly? What is it bound to that keeps it from just rising to the top of all the water and then exiting into the atmosphere?

Oxygen and other gases dissolved in water don't leave spontaneously when they are in balance with the amount of those same gases in the atmosphere. You can increase the amount of a gas in water by increasing the amount in the atmosphere, and vice versa.

This is why the rise in atmospheric CO2 concentrations is causing an increase in CO2 dissolved in the ocean, and is messing up corals and other calcifying organisms that are inhibited by the excess of CO2.

Also, water that is supersaturated with a gas (like Pepsi, with CO2) releases some of that gas as soon as atmospheric air hits the top of the soda when you open the can (it releases the CO2 until it is in balance with the level of CO2 in the atmosphere). Similarly, you can supersaturate a liquid with a gas simply by putting the liquid in a container and putting the gas on top of it and pressurizing the thing -- I have a cap that attaches to a bottle and hooks to a CO2 cylinder to carbonate individual bottles of homebrew (really strong beer is a bear to carbonate naturally, since the yeast dies at a certain alcohol content).

The first part of your question -- about just what 'dissolved' means in the case of oxygen -- I guess I don't understand myself. Here's an answer by someone who claims to be a Biochem Prof Emeritus (https://www.quora.com/How-does-oxyge...olar?share=1):

Q: "How does oxygen dissolve in water despite being non-polar?"

A:"Non polar molecules do fit into cavities in water, or rather, water forms cavities to accommodate them even though the free energy for doing so is unfavorable. Once in the cavity, non polar molecules do have a force of attraction with water, namely, van der Waals - London dispersion interactions. All molecules are attracted to each other via these forces, even in the absence of other forces such as hydrogen bonds and electrostatic interactions."

There are entries in Wikipedia for Van der Waals forces and London dispersion interactions, but I didn't get very far reading them (though there is a fun little historical aside in the Van der Waals entry about gecko toes).

I'm sort of surprised a real career chemist hasn't jumped in here to correct my probably sloppy explanations (no offense to Ed, who certainly has more chemistry background than I do).

I don't know about the salt question, but I understand that chlorine and sodium are both unstable as elements, so I'll guess the salt is in some sense primary.

There is a bunch of cool stuff to be learned about how the earth formed -- like the fact that all the water on Earth was formed elsewhere and came here on asteroid impacts really early on. I wouldn't be surprised if salt got here the same way.

Originally Posted by Lucille

Very interesting, all. So, what causes these dead zones? I remember when I had fish tanks I would only aerate one side of the tank, the circulating water would move in a way to homogenize the aerated water with the unaerated water and the fish never had problems. Aren't there all sorts of currents and tides that move ocean water around?

Generalized to make the topic simpler.
Water movement through the use of bubbles or other mechanical devices in aquaria don't really rely on bubbles themselves to supply the oxygen but the fact that it causes the water to circulate resulting in a large amount of surface area over time to be exposed to the atmosphere which allows for the exchange of gases between the tank and atmosphere. The same effect does occur on a larger scale via wind and currents but (hopefully) unlike your aquaria there are conditions that at that period of time renders the exchange as insufficient. In the case of the ocean anoxic zone, the nutrient load available to microbes results in the oxygen being consumed faster than it can be exchanged with the atmosphere. This is facilitated by what are known as facultative aerobic bacteria as they can switch from oxygen for respiration to other molecules like sulfur and back again depending on which method is more advantageous to the microbe(s). This is also not considering that the use of sulfur and other molecules results in waste that is toxic to obligate aerobic organisms (like hydrogen sulfide which is highly toxic). These problems can also be somewhat self-perpetuating if the nutrient flow is disrupted as the subsequent starvation and death of the microbes and other tolerant organisms release enough nutrients to cause a continuation the cycle.

A partial example of this occurs in the nitrogen cycle where microbes convert ammonia to nitrite to nitrate. The bacteria use the ammonia and nitrite as energy sources for oxygen free respiration (as the places the microbes live are oxygen limited biofilms).

Ed

Originally Posted by WebSlave

Yeah, kind of a serious question, to stimulate some discussion about just "things".

So that *free* oxygen that is not bound to hydrogen to form water is dissolved into what, exactly? What is it bound to that keeps it from just rising to the top of all the water and then exiting into the atmosphere?

And to keep this percolating, I was going to pose the question of where does the salt come from in the oceans, but that drills down to the question of where did the chlorine come from that makes salt? Whenever I look up where chlorine comes from, the answer is that it comes from salt. So this sort of sets up a "what came first, the chicken or the egg" sort of question.

We need to consider the aspects of what comprises a gas, liquid and solid as a base to discuss this with any clarity. For simplicity consider them to all be pure (so we avoid discussing things like interactions to form complexes, where the water actually reacts with a material like the formation of carbonic acid by CO2 and water reacting directly). So in the gaseous stage the molecules of water are far apart as the heat energy absorbed by the water prevents the molecules from clumping together (condensation). If you add a second gas to the gaseous water it is easy to mix as there is a lot of spaces between the molecules (ignoring effects of pressure of each gas on the other). In liquids like water since the atoms move around readily there is room between the molecules for other molecules to dissolve into the water. The amount that can dissolve depends on a variety of factors such as the temperature of the water but liquids have space for other items to dissolve. (Ignoring for the moment polar versus non-polar (like oil and water solutions). Finally solids are bound together in a crystalline structure which prevents the molecules from freely moving around (except for glass which is apparently a really slow moving liquid), as water freezes you actually can get the exclusion of other dissolved materials like salt ions via a process called fractional freezing. An old example of this was the concentration of alcohol in barrels of fermented ciders where the barrel(s) were allowed to freeze and once frozen a hole was melted into it allowing the alcohol to be decanted. (I used this in college with free gallons of apple cider for fun).

The fundamental origin of most of the elements heavier that helium are via the fusion reactions in stars, novae and supernovas. So they are present in the formation of a planet and depending on the reactions it undergoes either before or after planet formation gives you the compound. If exposed to water you can get several processes that can result in exchanges of cations (like how the rusting process includes the flow of an electrical current or in batteries where the ions can migrate between anode and cathode).

Ed

Originally Posted by Socratic Monologue

Oxygen and other gases dissolved in water don't leave spontaneously when they are in balance with the amount of those same gases in the atmosphere. You can increase the amount of a gas in water by increasing the amount in the atmosphere, and vice versa.

However you can't dissolve unlimited amounts of oxygen into water, once it is saturated (from all gases) you can't force anymore oxygen into it as the total amount of dissolvable gases depends on the amount (partial pressure) of each gas that is already present. Now if you heat up the water to drive all of the gases out of solution and then expose it to a pure oxygen atmosphere you can achieve a different saturation level of oxygen.

If you have a well and can draw really cold water from it, filling a glass should result in bubbles forming on the walls of the glass as it warms to room temperature. This is because the shift in temperature and pressure at which the water is held is pushing the gases out of solution.
A variation on this that frequently trips up novice aquarists or amphibian keepers is the pH difference between distilled and reverse osmosis water (RO). RO filters remove dissolved salts and should provide water that is close to a pH of 7, but generally RO right from the tank tends to have a pH between 5 and 6. The reason for this is because the filter doesn't remove dissolved CO2 gas, while removing all of the ions that might have buffered the water to a different pH. In water CO2 reacts with water molecules to form carbonic acid (H2CO3), and H2CO3 reacts with another water molecule forming HCO3+ and a hydrogen cation that associates with the negative side of the water molecule resulting in the pH drop. If the water is aerated and allowed to sit and come to room temperature, there is usually a shift towards a more neutral pH.
The interesting part is that this reaction is readily reversible and is used to carbonate beverages by saturating the beverage with CO2 which goes into solution and reacts as above but when the pressure on the liquid is released the gas comes out of solution and the reaction goes HCO3+ + H+ goes to CO2 gas plus H2O and the CO2 comes out of solution (why your soda goes flat)...


It has many years since I had to really think of P-chem problems and translate the concepts for those unfamiliar with the tech speak or symbols typically used.

Ed