Salt Water Swimming Pool Question.

In summary, salt water pools use an electrolysis cell to convert chloride ions into hypochlorous acid, the active sanitizer that kills harmful organisms in the water. This allows for lower levels of chlorine in the pool. Sodium chloride itself does not convert to hypochlorous acid, and the sodium in the pool likely stays in solution as an ion.
  • #1
Infrasound
70
0
How could sodium chloride produce chlorine (neutral atoms rather than ions) in a swimming pool?

I have always understood that chlorine takes an electron from sodium, because it's nucleus can pull more strongly on it. So, if the two were broken apart, wouldn't the chlorine keep the electron and be stable and therefore unable to do its job?

How does this work?
 
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  • #2
Infrasound said:
How could sodium chloride produce chlorine (neutral atoms rather than ions) in a swimming pool?

I have always understood that chlorine takes an electron from sodium, because it's nucleus can pull more strongly on it. So, if the two were broken apart, wouldn't the chlorine keep the electron and be stable and therefore unable to do its job?

How does this work?

The chlorine gets immediately converted into HOCl (hypochlorous acid).

"When any type of chlorine is added to water it ALL makes the SAME thing: Hypochlorous acid. It does not matter if it is Sodium Hypochlorite (liquid chlorine), Tri-chlor and Di-chlor or Lithium based, Cal-hypo or even gas chlorine--it all makes Hypochlorous acid. Hypochlorous acid is the active sanitizer; this is what kills algae and other harmful stuff in the water."
http://phoenix.about.com/cs/wet/a/saltpool01.htm


BTW, I Googled 'how does a saltwater pool work' and that came up as the second hit.


The only question I have is what happens to all the sodium?
 
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  • #3
[MODERATOR] Please move this to chemistry.

DaveC's answer is correct except for one significant detail. Sodium chloride is not one of the species that gets converted to hypochlorous acid. Chloride ions (Cl in -1 oxidation state) are quite stable .. much more so than other forms of chlorine, such as hypochlorous acid (Cl in +1 oxidatation state). Like the OP surmised, chlorine is a highly electronegative element ... once it gets that extra electron, it's not giving it back without a fight. In sciencey term, you need to add energy to convert chloride ions into just about any other chlorine containing compound.

So, to answer the OP's question .. salt water pools are NOT chlorinated simply due to the addition of sodium chloride. There is also an electrolysis cell which uses electrical energy to oxidize the chlorine atoms (i.e. to steal back that extra electron) so that they form hypochlorous acid. One supposed benefit of this is that the chlorine levels in the pool are much lower than for a normal chlorinated fresh water pool. My guess is that the tradeoff is that they require a lot more regular checking and maintenance to make sure that proper sanitizing is occurring ... however, that is only a guess.

[EDIT] To answer DaveC's question about what happens to all the sodium ... the answer is, probably not much. Sodium is much harder to reduce (i.e. give an electron back to) than chlorine is to oxidize. So, what most likely happens is that sodium stays in solution as an ion, while what gets reduced in the other half of the electrolysis cell is H+ ions. To satisfy charge conservation in an electrochemical reaction, you always need to have the same number of electrons involved in both the oxidation and reduction half-reactions. So, for each chloride ion that loses an electron in oxidation, another species must gain an electron. Based on experience, I am almost certain that it will be H+ ions getting reduced to form hydrogen gas, but I can't say for sure, since I have not studied all the equilibria involved with a salt-water pool.
 
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Related to Salt Water Swimming Pool Question.

1. What is a salt water swimming pool?

A salt water swimming pool is a pool that uses a salt chlorination system to sanitize the water instead of traditional chlorine. Salt water pools have a lower concentration of chlorine, making them gentler on the skin and eyes.

2. How does a salt water swimming pool work?

In a salt water pool, a salt chlorinator system is used to convert salt into chlorine through an electrolysis process. This chlorine then sanitizes the pool water, killing bacteria and algae. The process is constantly repeated, ensuring that the pool is always clean and safe to swim in.

3. Is a salt water swimming pool better for my health?

Salt water pools are often touted as being better for your health because they have a lower concentration of chlorine. However, the health benefits are debatable and ultimately depend on personal preference. Some people may find that salt water pools are less harsh on their skin and eyes, while others may not notice a difference.

4. Are salt water swimming pools more expensive?

The initial cost of installing a salt water pool may be more expensive than a traditional chlorine pool, as you need to purchase a salt chlorinator system. However, in the long run, salt water pools can save you money on pool maintenance and chemicals. You also won't need to purchase and handle chlorine, which can be a cost and safety concern for some pool owners.

5. Do I still need to test and balance the water in a salt water swimming pool?

Yes, just like any other type of pool, it is important to regularly test and balance the water in a salt water pool. While the salt chlorinator helps to maintain the chlorine levels, other factors such as pH, alkalinity, and calcium hardness still need to be monitored and adjusted as needed to keep the water clean and safe for swimming.

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