Can anyone answer where the chlorine atoms go?
They don't go anywhere. The process of oxidation is just chlorine atoms taking two electrons from something and becoming chloride.
Chlorine has 6 electrons in the outer shell and that gives the chlorine atom a +1 charge. In hypochlorous acid you have chlorine +1, oxygen -2 and hydrogen +1 for a net charge of 0. Hypochlorite has a chlorine +1 and oxygen -2 for a net charge of -1.
Chlorine atoms need 8 electrons in the outer shell to have a full shell. So, they take two from something like oxygen or nitrogen to fill their outer shell. This creates chloride with a charge of -1. Electrons each have a charge of -1, so as atoms gain electrons, their charge drops by 1 per gained electron.
A SWG plate has a positive charge that removes an electron from a chloride ion to make it into a chlorine atom with a charge of 0. Two chlorine atoms with a charge of 0 combine to make chlorine gas (Cl2), which dissolves into the water. When chlorine gas dissolves one atom ends up with a charge of -1 (chloride) and the other ends up with a charge of +1 and combines with oxide to form hypochlorite (OH-) or hypochlorous acid (HOCl).
With the outer shell full, the atom has a -1 charge.
In hypochlorite, oxygen has a -2 oxidation state. When the oxygen atom has a full outer shell of 8 electrons, it has a -2 oxidation state. This is its preferred state because it is the most stable state.
When UV light hits a hypochlorite ion, two electrons get knocked loose from the oxygen atom and the chlorine takes them. Oxygen doesn't really want to let them go but chlorine has a strong ability to take electrons.
This causes the oxygen to go from -2 (oxide) to an oxidation state of 0, which combines with another oxygen atom to form oxygen gas. Oxygen gas wants to get back the two electrons to get a full outer shell and it will oxidize something else if it gets a chance.
When oxidizing a nitrogen compound, like ammonia, chlorine again takes 2 electrons from the nitrogen, which changes it from -3 to 0. It takes 3 chlorine atoms to oxidize 2 nitrogen atoms in ammonia.
Ammonia is a chemical compound where the nitrogen is in the -3 oxidation state and there are 3 hydrogen ions in the +1 state. Because they are opposite charges, they combine together in an ionic bond.
When the nitrogen loses 3 electrons, its oxidation state goes to 0 and it can no longer combine with hydrogen to form ammonia. Nitrogen in the 0 oxidation state can combine with another nitrogen atom in the 0 oxidation state because they share electrons in a covalent bond.
This is how ammonia is oxidized into nitrogen gas. The nitrogen goes into the atmosphere and the ammonia is gone. It leaves the hydrogen ions behind, so it is acidic.
CCs are not created by chlorine oxidizing something.
CCs are only created if chlorine "combines" with something.
For example, ammonia is NH3 or NH4. Chlorine can either oxidize the nitrogen or it can replace a hydrogen ion and combine with the ammonia molecule.
Chlorine can replace 1, 2 or 3 hydrogen ions to form NH2Cl (monochloramine), NHCl2 (dichloramine) or NCl3 (trichloramine aka nitrogen trichloride). Nitrogen trichloride is a gas and is what you smell when a pool has a "chlorine" smell. It's also the toxic gas generated if you mix bleach and ammonia. It's not chlorine gas, but it is a chlorinated gas that's highly toxic and even explosive if it is concentrated enough.
Combined chlorine only happens if chlorine combines, not when it oxidizes.
When chlorine reacts with algae, it's usually just an oxidation reaction and no combination occurs.
Plants, such as algae, create chemicals like glucose from carbon dioxide and water. Using light, the carbon in carbon dioxide oxidizes the oxide into oxygen.
6CO2 + 6H2O --> C6H12O6 + 6O2
Carbon dioxide + water--> glucose + oxygen.
This is how plants make oxygen and store energy in sugars. Most of the bulk of plants is carbon from carbon dioxide. Most of the weight of a tree comes from the air.
The carbon in carbon dioxide is in the +4 state.
The carbon in glucose is 4 at 0, 1 at -1 and 1 at +1. The carbon is "reduced", which is the opposite of oxidized. Reduced just means that the oxidation state is lower or reduced because the atom gained electrons which are negatively charged.
When chlorine oxidizes the carbon in glucose back to a +4 oxidation state, it reverts back to carbon dioxide.
This is a similar process to an animal using oxygen to burn sugars to release energy and exhale carbon dioxide.
So, chlorine reacting with algae is mostly an oxidation reaction and not a combination. Algae is mostly converted back into carbon dioxide and water.
Chlorine can combine with carbon compounds, such as methane (CH4) by replacing the hydrogen ions.
Carbon in methane is in the -4 oxidation state.
Chlorine killing algae usually does not create any CCs.
Chlorine lost to UV does not create CCs.
CCs are mostly nitrogen compounds. UV helps break down CCs the same way that it causes hypochlorite to be lost, by knocking the electrons loose from the nitrogen so that the chlorine can more easily take them.
Nitrogen compounds are mostly introduced by bather waste such as urine or sweat.
The only really big source of ammonia is if bacteria eat the cyanuric acid and break it down into ammonia.
So, basically, the process of chlorine oxidizing something is just the chlorine atom taking 2 electrons and becoming chloride. The process of becoming chlorine again is just removing 2 electrons to activate the atom again.
Most of chemistry is atoms gaining or losing electrons and then combining or dissociating based on the oxidation states.
If you want to know the oxidation states of the atoms in a chemical compound, go to wolframalpha and enter the chemical and oxidation states. For example, hypochlorite oxidation states or ammonia oxidation states etc.
