Swimming Pool Chemistry involves a rich variety of chemical concepts and applications. In this paper, it was describe how the various principles apply to chlorination in swimming pools, but these principles also apply to chlorination of drinking water, to wastewater treatment and even to small irrigation systems. It's fair to say that Chlorine has had a lot of bad press lately. This is high interest way to talk about the proper use of very common household chemicals. With factual information, and by insisting on careful work using microchemistry techniques, it has to appropriate respect without fear for these chemicals that are in widespread consumer use. Chlorination of water is used in many situations other than the backyard pool and each application has its own variations that must be taken into account. An important example is the formation of chloramines by the reaction of chlorine with nitrogen-containing organic matter. Chloramines are very toxic to fish, so conditions are sought to avoid their formation in the chlorination of sewage effluent. In swimming pools, they are nuisance chemicals, lowering the effectiveness of the chlorine load in the pool and leading to eye and skin irritation. In treatment of drinking water, however, they are advantageous, as low-level disinfectants that reside in the water long after hypochlorite have broken down. In Walkerton Ontario, Canada, over 2000 of the town's 7000 residents were hospitalized and seven deaths resulted from a malfunction of the municipal chlorination system and contamination of the water supply with a virulent strain of e-coli bacteria. Most home pools and hot tubs use chlorine for water treatment and chlorine has become more common as an ingredient in cleansers.
Chemistry involved
Chlorination
There are a variety of ways to introduce chlorine into water. Direct bubbling of gaseous chlorine, addition of OCI2, electrolysis of NaCI in saltwater pools, etc. The most widely used method is addition of hypochlorite of sodium, calcium or lithium. Each of these salts has advantages and disadvantages in price and solubility. Slow dissolving calcium hypochlorite is easily compressed into pucks, but leaves a white insoluble residue that must be filtered out to maintain water clrity. Although more expensive, lithium salt dissolves quickly and completely and is preferred in hot tubs where the rate of chlorine loss is high. Once in the water, equilibrium is established between the strong oxidant HCLO and the weaker CLO-ion. The equation was as the following..
H2O + HOCL ↔ H3O+ + OCL- Ka = 3 Ã- 10-8
The negative charge on the hypochlorite ion hinders passage through bacterial membranes, so HOCL is the preferred species to oxidize the cell contents. Conversion of almost all free chlorine to HOCL is easily accomplished by dropping the pH to 6 or so.
The equilibrium is pH dependendent and is very sensitive in the range of pH 7 to 8.
At a pH of 2 or lower, chlorine gas is evolved and even mildly acidic water will corrode metalsand grouting in tiled pools. The addition of calcium ions to the water to minimize leaching of tile grout is an interesting example of the common ion effect in solubility.
In acid water, the sulphate can combine with H+ ions to form HSO4-
CaSO4(s) ↔ Ca2+ (aq) + SO42- (aq) + H+ (aq) ï‚«ï€ ïˆSO4- (aq) (this was another equilibrium, we can add with CaCl2 to form HSO4-)
To prevent this, extra calcium can be added (as CaCl2) shifts the equilibrium in the direction of the solid CaSO4-. Low calcium ion levels combined with low pH in pool water can lead to leaching of copper from pipes and that can lead to "green hair". If the water becomes acidic, copper elements in the pool heater, copper pipes and bronze pump impellers all leach copper ions into the water.
Chloramines
The tendency of ammonia and ammonia-like compounds (including proteins) to react with HOCL forming chloramines is very important:
NH3 + HOCl ï‚« NH2Cl + H2O
NH2Cl + HOCl ï‚« NHCl2 + H2O
Chloramines are mildly toxic to bacteria, but tend to be irritating to eyes and skin, so they are unwelcome additions to the pool. Fortunately, chloramines react with each other, as
NH2Cl + NHCl2 ï‚« N2(g) + 3 HCl
If too much HOCl is available, an undesirable competing reaction takes place.
NHCl2 + HOCl ï‚« NCl3 + H2O
Nitrogen trichloride is very irritating to eyes and mucous membranes. It offgases to the air creating a distinctive "swimming pool" smell that most people identify as the smell of chlorine. Ironically, if the pool has the correct levels of chlorine, there will be little if any odour. "Superchlorination" is used to rid pools of chloramines that build up through reaction with protein and other byproducts of humans swimming in the pool.
2 NH3 + 3 HOCl ï‚« N2(g) + 3 HCl + 3 H2O
Buffering:
Buffering is a second equilibrium reaction to counter shift in equilibrium. To maintain a stable pH level in the desired range, sodium bicarbonate can be added in amounts of about 100mg/kg [about 6 kg for a medium sized 60,000 L pool]. Fortunately, as the pH goes down, more HClO is formed from ClO- ions and the germicidal activity of the residual free chlorine actually increases.
Losses in Sunlight:
Hypochlorite undergoes rapid photolysis in the presence of UV light. [ï¬ = 290 to 350 nm] from sunlight. About 90% of chlorine consumed by outdoor pools is the lost due to the photolysis reactions: 2 OCl- + ï®ïï® â†’ 2 Cl- + O2(g)
And 2 HOCl- + ï®ïï® â†’ 2 HCl + O2(g)
To stabilize chlorine levels, the herbicide isocyanuric acid [toxic to radishes and barley] is added to the water and reacts with OCl- to give dichloro(iso)cyanuric acid. This is not broken down by sunlight, but the equilibrium reaction will shift to compensate for losses of OCl-.
In this way cyanuric acid acts as a "chlorine buffer" for outdoor pools. Its effect of adding an excess of cyanuric acid would be on the chlorine levels required for sanitation. It is an excellent example of how Le Chatelier's Principle shows that "More" is not always "Better".
Focus question:
What affect to pH and why is it important?
Answer: pH is a measure of how acid or how alkaline the water is. For example, lemons and cooking apples are sour and acidic and have a low pH. Soda crystals and bicarbonate of soda are alkaline and have a high pH. In the pool, the pH should be Between 7.2 and 7.6, but keep it as near as possible to 7.2 if you are using Granular shock. This is a compromise as the chlorine would be more effective if the pH was slightly below 7.0, but this would lead to potentially corrosive conditions. Also, the human body is most comfortable bathing in water of pH approx. 7.4. In some water areas, especially in the south of England, the water is hard because it contains dissloved calcium or magnesium salts and, therefore, has a naturally high pH. the pH is kept at the same level as that in our eyes, the side-effects of burning red eyes is kept to a minimum. The ability of chlorine to disinfect at this level is also optimum. High water temperatures tend to raise the pool water pH; rainwater can lower pH. The type of sanitiser you use also has a bearing on pH. It is important to measuring your pool with pH. you should bear in mind the pH scale is not uniform. pH 8.0 is 10 times more alkaline than pH 7.0. pH 9.0 is 100 times more alkaline than pH 7.0. So small differences can be significant. pH is one of the most important aspects of swimming pool care. Low pH can lead to skin irritation and corrosion of pool equipment. High pH can result in cloudy water and contribute to scale formation. More importantly, high pH will reduce the effectiveness of the sanitiser as it releases less free active chlorine. pH is one of the most important aspects of swimming pool care. Low pH can lead to skin irritation and corrosion of pool equipment. High pH can result in cloudy water and contribute to scale formation. More importantly, high pH will reduce the effectiveness of the sanitiser as it releases less free active chlorine. pH is one of the most important aspects of swimming pool care. Low pH can lead to skin irritation and corrosion of pool equipment. High pH can result in cloudy water and contribute to scale formation. More importantly, high pH will reduce the effectiveness of the sanitiser as it releases less free active chlorine. pH is one of the most important aspects of swimming pool care. Low pH can lead to skin irritation and corrosion of pool equipment. High pH can result in cloudy water and contribute to scale formation. More importantly, high pH will reduce the effectiveness of the sanitiser as it releases less free active chlorine. In the chlorination, it talked about once in the water, equilibrium is established between the strong ocidant HClO and the weaker ClO- ion. The negative charge on the hypochlorite ion hinders pass through bacterial mambranes, so HOCl is the preferred species to oxidize the cell contents. Although, the pH is very important for pool. If low pH in swimming Pool, the following things will be happen. The pool will plaster or grouting, will get burning eyes and nose, dry and itchy skin and scalp, perishing of swimwear, pool toys and accessories. Other hand, if high pH in swimming Poll, some problem will be follow up such as: scaling or calcium buildup on pool surfaces, waterline and accessories, the dull or cloudy pool water, clogging of filter medium or elements, drop in disinfection potential of chlorine resulting in algae growth, burning eyes and nose, dry itchy skin and scalp. Therefore, it was very important to measure the pool with pH.
Q2. What kind of disaster can happen if a chlorination system goes wrong and contamination of drinking water resulted?
Answer: chloramines are very toxic to fish, so conditions are sought to avoid Chloramines are very toxic to fish, so conditions are sought to avoid their formation in the chlorination of sewage effluent.In swimming pools, they are nuisance chemicals, lowering the effectiveness of the chlorine load in the pool and leading to eye and skin irritation. In treatment of drinking water, however, they are advantageous, as low-level disinfectants that reside in the water long after hypochlorites have
broken down. In fact, the City of Virginia Beach VA recently converted from Chlorine to Chloramines as the treatment of choice for drinking water. In many North American municipalities, greater attention is being paid to the treatment of drinking water after some widely publicized failures of the treatment process. In Walkerton Ontario, Canada, over 2000 of the town's 7000 residents were hospitalized and seven deaths resulted from a malfunction of the municipal chlorination system and contamination of the water supply with a virulent strain of e-coli bacteria. Since the Walkerton disaster, every tourist resort owner in the Province of Ontario who treats surface water for domestic use must attend a weeklong course in Water Treatment and pass a rigorous exam at the end. The exam deals with such topics as flow rates, chloramine formation, pH, alkalinity and buffer capacity to mention just a few. Particularly, if young kids "poo" defecate in the pool as human faces have dangerous bacteria 'e - coli' which can cause major health issue. If someone sawn with a staphlouces infection, common cold, flu or indeed any nasty bacteria, these can be transferred to other through mouth, eyes, even sikin. Chlorine Oxidises (kills) bacteria. Therefore, some kind of disaster like getting unhealthy through to our body skin and the end way is to death if drinking of it, can happen if a chlorination system go wrong and contamination of drinking water.
Q3. What factors impact available chlorine in a pool?
Answer: Chlorine is a greenish-yellow gas that dissolves easily in water. It has a pungent, noxious odour that some people can smell at concentrations above 0.3 parts per million. Because chlorine is an excellent disinfectant, it is commonly added to most drinking water supplies. In parts of the world where chlorine is not added to drinking water, thousands of people die each day from waterborne diseases like typhoid and cholera. Chlorine is also used as a disinfectant in wastewater treatment plants and swimming pools. It is widely used as a bleaching agent in textile factories and paper mills, and it's an important ingredient in many laundry bleaches. When chlorine is added to water, it causes a reaction which produces HOCl (hypochlorous acid) + HCl (hydrochloric acid). Hypochlorous acid is the active (bacteria-killing) form of chlorine, which sanitizes water. Chlorine kills microorganisms by breaking through the cell walls and destroying the inner enzymes, which in turn deactivates, or oxidizes the cells. The hypochlorous molecule continues this process until it either combines with nitrogen or ammonia compounds to become a chloramine, or it is broken down into its component atoms, becoming de-activated itself. People who are adding chlorine to water for disinfection must be careful for two reasons: 1) Chlorine gas even at low concentrations can irritate eyes, nasal passages and lungs; it can even kill in a few breaths; and 2) The formation of THM (trihalomethanes) compounds must be minimized because of the long-term health effects.
Q4. Why do you add Sodium bicarbonate? What does Sodium Bicarbonate do?
Answer: To maintain a stable pH level in the desired range, Sodium bicarbonate can be added in amounts of about 100 mg/kg [about 6 kg for a medium sized 60,000 L pool]. Fortunately, as the pH goes down, more HClO is formed from ClO- ions and the germicidal activity of the residual free chlorine actually increases. Since the use of NaOCl or Ca(OCl)2 will slowly tend to raise the pH, acid salts like NaHSO4 can be used to lower it. In some commercial pool, CO2 is bubbled into the water to shift the bicarbonate equilibrium to a lower pH and Na2CO3 is used to raise it. We add sodium bicarbonate to raise alkalinity, and it raises ph which triggers the ph monitor to lower the ph which is the same chemical that lowers alkalinity. Usually if we turn off the pump to let the sodium bicarbonate do, it's thing. Is there a better way to add the sodium bicarbonate so that we don't have to turn the pump off. So it's a easy way for people who can forgot often. The sodium bicarbonate also cleaning the pool when u add them in swimming pool.
