DavidArmenB
Well-known member
- Sep 7, 2022
- 262
- Pool Size
- 16500
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
I am also in the crew who say it should be called a SWCG, not just a SWG.
For anyone who is curious, this is the method of operation of SWCGs:
The device uses electrolysis to electrically charge the salt water which sustains a reaction with the water (H2O) and the dissolved Sodium Chloride (table salt, NaCl) which in turn splits the salt into Chlorine Gas (Cl2), with byproducts of Hydrogen gas (H2), hydroxide ions (OH-), and metallic Sodium ions (Na+), which then go on to have reactions of their own.
Here is the chemistry behind the method of operation:
The salt dissolves in water.
4NaCl → 4Na+ + 4Cl−
The ions combine via electrolysis of the SWCG.
4Na+ + 4Cl− → 4Na + 2Cl2
The leftover metallic Sodium then reacts with the water.
4Na + 4H2O → 4Na+ +4OH− + 2H2
Then is the hydrolysis of aqueous Chlorine Gas.
2Cl2 + 2H2O → 2HClO + 2H+ + 2Cl−
Finally, the dissociation of hypochlorous acid.
2HClO → HClO + ClO− + H+
This is the net reaction when combining all of the individual reactions above.
4NaCl + 3H2O → 4Na+ + HClO + ClO− + OH− + 2Cl− + 2H2
(Table salt reacts with water to form Sodium Ions, Hypochlorous acid, Hypochlorite, Hydroxide, Chloride ions, and Hydrogen gas)
As stated, other reactions occur afterwards, such as the Chloride ions (Cl-) combining with each other to form Chlorine gas (Cl2).
2Cl− → Cl2 + 2e−
The tiny bubbles you see coming out of the returns when operating a SWCG is gaseous hydrogen. Unlike chlorine gas, hydrogen does not dissolve into the water, so when it gets pushed out of the returns, it quickly escapes into the atmosphere (and eventually into outer space).
Why does pH rise more quickly when operating a SWCG?
pH (potential of Hydrogen) is just a scale for the ratio between Hydrogen ions and Hydroxide ions (hydroxyl) in the solution (pool water). pH is neutral (pH 7.0) when the number of hydrogen ions (H+) equal the number of hydroxide ions (OH-); they can combine to form water molecules (H2O). pH is basic (high pH, >7.0) when there are more hydroxide ions than hydrogen ions. Conversely, pH is acidic (low pH, <7.0) when there are more hydrogen ions than hydroxide ions.
The reason we keep needing to add Acid more often when we operate SWCGs is because the salt water chlorination process produces an excess of hydroxide ions, increasing the pH of the water, which in turn requires the frequent addition of Hydrochloric Acid (HCl, also known as Muriatic Acid) to increase the number of hydrogen ions and equalize the ratio between hydrogen ions and hydroxide ions, which neutralizes the alkalinity and balances pH.
For anyone who is curious, this is the method of operation of SWCGs:
The device uses electrolysis to electrically charge the salt water which sustains a reaction with the water (H2O) and the dissolved Sodium Chloride (table salt, NaCl) which in turn splits the salt into Chlorine Gas (Cl2), with byproducts of Hydrogen gas (H2), hydroxide ions (OH-), and metallic Sodium ions (Na+), which then go on to have reactions of their own.
Here is the chemistry behind the method of operation:
The salt dissolves in water.
4NaCl → 4Na+ + 4Cl−
The ions combine via electrolysis of the SWCG.
4Na+ + 4Cl− → 4Na + 2Cl2
The leftover metallic Sodium then reacts with the water.
4Na + 4H2O → 4Na+ +4OH− + 2H2
Then is the hydrolysis of aqueous Chlorine Gas.
2Cl2 + 2H2O → 2HClO + 2H+ + 2Cl−
Finally, the dissociation of hypochlorous acid.
2HClO → HClO + ClO− + H+
This is the net reaction when combining all of the individual reactions above.
4NaCl + 3H2O → 4Na+ + HClO + ClO− + OH− + 2Cl− + 2H2
(Table salt reacts with water to form Sodium Ions, Hypochlorous acid, Hypochlorite, Hydroxide, Chloride ions, and Hydrogen gas)
As stated, other reactions occur afterwards, such as the Chloride ions (Cl-) combining with each other to form Chlorine gas (Cl2).
2Cl− → Cl2 + 2e−
The tiny bubbles you see coming out of the returns when operating a SWCG is gaseous hydrogen. Unlike chlorine gas, hydrogen does not dissolve into the water, so when it gets pushed out of the returns, it quickly escapes into the atmosphere (and eventually into outer space).
Why does pH rise more quickly when operating a SWCG?
pH (potential of Hydrogen) is just a scale for the ratio between Hydrogen ions and Hydroxide ions (hydroxyl) in the solution (pool water). pH is neutral (pH 7.0) when the number of hydrogen ions (H+) equal the number of hydroxide ions (OH-); they can combine to form water molecules (H2O). pH is basic (high pH, >7.0) when there are more hydroxide ions than hydrogen ions. Conversely, pH is acidic (low pH, <7.0) when there are more hydrogen ions than hydroxide ions.
The reason we keep needing to add Acid more often when we operate SWCGs is because the salt water chlorination process produces an excess of hydroxide ions, increasing the pH of the water, which in turn requires the frequent addition of Hydrochloric Acid (HCl, also known as Muriatic Acid) to increase the number of hydrogen ions and equalize the ratio between hydrogen ions and hydroxide ions, which neutralizes the alkalinity and balances pH.
