Pool Chemistry Certified-residential Exam

Buffers are substances that help maintain the pH of a solution by resisting changes in acidity or alkalinity. They achieve this by accepting or donating protons to prevent the concentration of hydrogen ions from changing significantly. In other words, buffers can neutralize small amounts of added acid or base, preventing drastic changes in pH. Therefore, the statement that buffers prevent, inhibit, or slow down pH change due to small amounts of acid or base is true.

Mixing trichlor (trichloroisocyanuric acid) with cal hypo (calcium hypochlorite) can indeed cause a fire and explosion. Trichlor is a strong oxidizing agent, and when it comes into contact with cal hypo, which is also an oxidizing agent, a highly reactive and dangerous mixture is created. This combination can release large amounts of heat and oxygen, leading to a fire and potential explosion. It is important to handle these chemicals with caution and avoid mixing them together to prevent any accidents or hazards.

The statement is true because AOP (Advanced Oxidation Process) does indeed involve the use of ozone, hydrogen peroxide, and UV to generate hydroxyl radicals. These hydroxyl radicals are highly reactive and can effectively break down and remove organic matter. Therefore, the given statement accurately describes the process of AOP.

UV light is commonly used for disinfection purposes because it has the ability to kill or inactivate microorganisms, such as bacteria and viruses, by damaging their DNA or RNA. This makes it an effective method for sterilizing water, air, and surfaces. Additionally, UV light can also help in removing combined chlorine, which is formed when chlorine reacts with organic matter in water. The UV radiation breaks down the combined chlorine compounds, leading to their removal. Therefore, the statement that UV light is used for disinfection and combined chlorine removal is true.

Ozone (O3) is known to be a strong oxidizer, meaning it has the ability to remove electrons from other substances. The statement suggests that ozone is 25 times more powerful than HOCl (hypochlorous acid), 2500 times more powerful than OCl- (hypochlorite ion), and 5000 times stronger than chloramine. This implies that ozone has a significantly higher oxidizing capacity compared to these other substances, making the statement true.

Sodium hypochlorite is commonly used as a disinfectant and bleach, and it contains chlorine. The statement is stating that one gallon of liquid chlorine, specifically sodium hypochlorite with a concentration of 12.5%, contains approximately 1 lb of pure chlorine. This means that the chlorine content in the liquid chlorine is about 1 lb, making the statement true.

When salt is dissolved in water, the sodium and chloride ions separate from each other and become surrounded by water molecules. These ions are charged particles, with sodium having a positive charge and chloride having a negative charge. This separation of charges creates an electrical imbalance in the solution, similar to many tiny electrical plates or poles. Therefore, the statement that ions formed when salt is dissolved in water are positively and negatively charged like many tiny electrical plates or poles is true.

Chlorine gas is produced at the positive electrode of a saltwater chlorine generator. This is because when an electric current is passed through the saltwater solution, a chemical reaction occurs at the positive electrode, known as the anode. This reaction causes chloride ions (Cl-) to lose an electron and form chlorine gas (Cl2). Therefore, it is true that chlorine gas is produced at the positive electrode of an SWG.

When 1 lb of cal hypo 65% is added to 10,000 gallons, it results in a concentration of about 8.0 ppm (parts per million). This means that there are 8.0 parts of cal hypo 65% per million parts of the solution. Therefore, the statement is true.

Cyanuric acid, also known as CYA, increases the amount of free chlorine needed to effectively control bacteria and algae in a pool. This is because CYA acts as a stabilizer for chlorine, preventing it from being rapidly degraded by sunlight. Without CYA, the chlorine would dissipate quickly, requiring more frequent additions of chlorine to maintain proper sanitation levels. Therefore, it is true that CYA increases the free chlorine requirement for controlling bacteria and algae.

Adding muriatic acid, which is a strong acid, to water will lower the total alkalinity. The acid reacts with the alkaline compounds in the water, reducing their concentration and thus lowering the alkalinity. Therefore, adding 25.6 fl oz of muriatic acid to 10,000 gallons of water will indeed lower the total alkalinity by 10 ppm.

The use of CYA (cyanuric acid) in indoor pools can indeed provide benefits. CYA is a stabilizer that helps protect chlorine from being rapidly degraded by sunlight. While indoor pools are not exposed to direct sunlight, CYA can still be beneficial as it helps to maintain a consistent chlorine level and reduces the need for frequent chlorine additions. This can result in cost savings and improved water quality in indoor pools.

The correct answer is true because most salt water chlorine generators (SWG) require a salt concentration of 3,000 to 3,500 parts per million (ppm) in order to effectively generate chlorine. This concentration is necessary for the SWG to function properly and maintain the desired level of chlorine in the pool water.

Adding borate to water can act as a pH buffer, preventing the pH from increasing. Borate ions can react with hydroxide ions, which are responsible for increasing the pH, forming a weak base and water. This reaction helps to maintain the pH at a relatively constant level, making it true that adding borate to water can prevent the pH from going up.

The correct answer is calcium carbonate saturation because the LSI (Langelier Saturation Index) is a measure of the tendency of water to deposit or dissolve calcium carbonate. It is used to determine the scaling or corrosive potential of water in relation to calcium carbonate. By calculating the LSI, one can assess whether the water is under-saturated, balanced, or over-saturated with calcium carbonate, which helps in understanding its scaling or corrosive behavior.

Trichlor and dichlor are types of chlorine compounds commonly used in swimming pools. These compounds are acidic in nature and have a low pH. When added to pool water, they can lower the pH level and also reduce the total alkalinity. This is because the compounds release hydrogen ions, which increase the acidity of the water. As a result, the pH level decreases and the total alkalinity is also affected. Therefore, the statement that trichlor and dichlor are acidic and can lower the pH and total alkalinity of pool water is true.

With 30 ppm CYA (Cyanuric Acid) in the water, it forms a complex with chlorine, reducing its effectiveness. This means that 97% of the chlorine is bound to CYA, leaving only 3% of the chlorine available for its intended purpose of killing bacteria and oxidizing contaminants. Therefore, the statement is true.

When sodium carbonate (soda ash) is added to pool water, it will raise both the pH and total alkalinity levels. Sodium carbonate is a basic compound that acts as a pH increaser. It helps to raise the pH level of the water, making it less acidic. Additionally, sodium carbonate also increases the total alkalinity of the water, which is the measure of its ability to resist changes in pH. Therefore, adding sodium carbonate to pool water will have the effect of raising both the pH and total alkalinity levels.

The white flakes in a SWG pool are deposits that were on the SWG plates that came off when the polarity was reversed. When the polarity of the SWG (Salt Water Generator) is reversed, it causes a process called electrolysis. This process can cause the deposits that have built up on the SWG plates to loosen and come off, resulting in white flakes in the pool. These flakes are the remnants of the deposits that were on the SWG plates.

Adding calcium chloride and sodium bicarbonate at the same time to water is not okay because they have opposite effects on water hardness. Calcium chloride increases water hardness by adding calcium ions, while sodium bicarbonate decreases water hardness by adding bicarbonate ions. Adding them together would result in a neutralizing effect and could potentially lead to an imbalance in water chemistry. Therefore, it is not recommended to add them simultaneously.

One cubic foot is equal to 7.48 gallons of water. This conversion is based on the fact that one gallon is equal to 0.1337 cubic feet. Therefore, to find the number of gallons in one cubic foot, we can multiply 1 by 7.48, resulting in 7.48 gallons.

A change in temperature by 15°F will result in a change of 0.1 in the Langelier Saturation Index (LSI). The LSI is a measure of the potential for calcium carbonate to precipitate or dissolve in water. When the LSI is positive, there is a tendency for scale formation, while a negative LSI indicates a tendency for corrosion. A change in temperature affects the solubility of calcium carbonate, which in turn affects the LSI. Therefore, a change of 15°F will cause a small change of 0.1 in the LSI.

In a new plaster pool, it is recommended to wait 28 days before adding the required amount of salt for an SWG. This waiting period allows the plaster to cure properly and prevents any potential damage or discoloration that could occur if salt is added too soon. Waiting for 28 days ensures that the plaster is fully set and ready to withstand the saltwater environment created by the SWG.

Water has a density of 8.34 pounds per gallon at room temperature. This means that 1 gallon of water weighs 8.34 pounds.

Bromine tabs are typically made of BCDMH, which stands for bromochloro-5,5-dimethylhydantoin. BCDMH contains both bromine and chlorine, making the answer "chlorine" correct.

The presence of 2.0 ppm free chlorine in the water with a pH of 7.5 and 30 ppm of CYA (cyanuric acid) will not kill algae. The reason for this is that while free chlorine is effective in killing algae, the presence of CYA at 30 ppm inhibits the effectiveness of chlorine. CYA acts as a stabilizer for chlorine, protecting it from degradation by sunlight. However, at high levels like 30 ppm, CYA can also reduce the sanitizing power of chlorine, making it less effective in killing algae. Therefore, even with a sufficient level of free chlorine, the presence of high CYA levels can prevent it from effectively killing algae.

Pool water needs to have a minimum calcium hardness of 150 ppm to prevent it from becoming aggressive. If the calcium hardness is below this level, the water can become corrosive and damage the pool's surfaces and equipment. Having the correct calcium hardness level helps to maintain a balanced and stable pool environment.

Lowering the total alkalinity of the pool water will reduce its ability to resist changes in pH. Therefore, if the pH of the pool water is always increasing, lowering the total alkalinity will slow down the rate of increase as the water will be less resistant to pH changes.

The minimum calcium hardness needed to balance the water is 150 ppm. Calcium hardness refers to the concentration of calcium ions in the water, and it is important to maintain a certain level to prevent corrosion of metal surfaces, such as pipes and fixtures. A calcium hardness level below 150 ppm can lead to the water becoming too soft, which can cause these metal surfaces to deteriorate. Therefore, a minimum calcium hardness of 150 ppm is necessary to ensure water balance and prevent damage.

Pouring acid into the water while standing in one place or adding acid in a column into the water will not only lower total alkalinity. This is because when acid is added to water, it reacts with the alkaline substances present in the water, causing a decrease in alkalinity. However, it can also affect other properties of the water such as pH levels and acidity. Therefore, the statement is false as it does not consider the potential impact on other water properties.

This statement is false because algae can still grow even if the free chlorine level in the water is between 2.0 and 4.0 ppm. While maintaining a free chlorine level within this range can help control and prevent algae growth to some extent, it does not completely eliminate the possibility of algae growth. Other factors such as sunlight exposure, nutrient levels, and temperature can also contribute to the growth of algae in water.

The correct answer is 15,147 gallons. To calculate the volume of the pool, we multiply the length (30') by the width (15') by the average depth (4.5'). This gives us a volume of 2025 cubic feet. Since there are 7.48 gallons in a cubic foot, we multiply the volume by 7.48 to get the total number of gallons, which is 15,147 gallons.

The correct answer is 7.5%. The free chlorine level should be 7.5% of CYA (Cyanuric Acid) to effectively kill algae in the absence of borate. Cyanuric Acid helps stabilize the chlorine and prevent it from being quickly degraded by sunlight. Maintaining a free chlorine level of 7.5% of CYA ensures that there is enough chlorine present to effectively eliminate algae and maintain a clean and safe swimming pool.

Aeration and turbulence can increase the pH of pool water without affecting its alkalinity. This is because aeration introduces oxygen into the water, which reacts with carbon dioxide to form carbonic acid. This acid then dissociates into hydrogen ions and bicarbonate ions, raising the pH. However, alkalinity is a measure of the water's ability to resist changes in pH, so it remains unaffected by the aeration and turbulence. Therefore, the statement is true.

The target free chlorine level is calculated by multiplying the CYA level by 0.075, which gives a target of 3.75 ppm. Since the current free chlorine level is 2.0 ppm, the technician needs to raise it by 1.75 ppm (3.75 ppm - 2.0 ppm). The liquid chlorine concentration is 12.5%, so to raise the free chlorine by 1.75 ppm, the technician needs to add a certain volume of liquid chlorine. By using the dosage chart or app, it is determined that the technician needs to add 34.5 fl oz of liquid chlorine to achieve the desired level.

The PCTI (Prescription and Care of the Intensive) recommends a target pH of 7.5. This means that in order to maintain optimal health and functioning, it is recommended to keep the pH level of the body within the range of 7.2 to 7.6. A pH level of 7.5 is considered slightly alkaline, which is believed to support various bodily functions and promote overall well-being.

Cyanuric Acid (CYA) does more than just protect chlorine in water from degradation by sunlight. It acts as a stabilizer for chlorine, helping it last longer in the water and reducing the amount of chlorine needed to maintain proper disinfection levels. CYA also helps to prevent chlorine loss due to evaporation. Therefore, the statement that CYA does not do anything else in the water is incorrect.

The correct answer is 90 ppm. The PCTI (Pool & Hot Tub Alliance) recommends a target for Total Alkalinity of 90 ppm. Total Alkalinity is a measure of the water's ability to resist changes in pH. Maintaining the alkalinity within the recommended range helps to stabilize the pH levels in the pool or hot tub, preventing fluctuations that could lead to water balance issues or discomfort for swimmers. Therefore, it is important to aim for a Total Alkalinity of 90 ppm to ensure proper water chemistry and a pleasant swimming experience.

The answer is 10,000 because ppm stands for "parts per million," which is a unit used to express small concentrations of a substance in a solution. 1% is equivalent to 10,000 parts per million, meaning that for every million parts of the solution, 10,000 parts are the substance in question.

In the absence of cyanuric acid (CYA), chlorine is more susceptible to degradation by sunlight. This is because CYA acts as a stabilizer, protecting chlorine from the harmful effects of UV rays. Without CYA, chlorine can be rapidly broken down by sunlight, resulting in a higher percentage of chlorine loss. Therefore, it can be inferred that 75% of chlorine is lost to sunlight in 2 hours without CYA.

Trichlor is a type of chlorine compound that contains cyanuric acid (CYA) as a stabilizer. When trichlor is added to the water, it releases chlorine and also increases the level of CYA. For every 10 ppm of chlorine added by trichlor, the CYA level will increase by 6 ppm. This means that the CYA level increases at a lower rate compared to the chlorine level.

When CO2 dissolves in water, it forms carbonic acid, which lowers the pH of the water. Removing CO2 from the water will disrupt this equilibrium, causing the concentration of carbonic acid to decrease. As a result, the pH of the water will increase, leading to a higher pH.

The recommended target for cyanuric acid (CYA) without a saltwater chlorine generator (SWG) is 50 ppm. CYA is a stabilizer that helps protect chlorine from being degraded by sunlight. It is important to maintain an appropriate CYA level to ensure effective disinfection and prevent excessive chlorine loss. Too low a CYA level may result in rapid chlorine depletion, while too high a level can reduce chlorine's effectiveness. Therefore, a target of 50 ppm is recommended to strike a balance and optimize chlorine efficiency.

The PCTI (Plasterers' Craftsmanship Training Institute) recommends a target of 350 ppm (parts per million) for calcium hardness for plaster pool surfaces. Calcium hardness refers to the amount of dissolved calcium in the water, and maintaining it within the recommended range helps prevent issues such as scale formation, etching of plaster surfaces, and corrosion of pool equipment. A higher calcium hardness level can lead to cloudy water and scaling, while a lower level can cause the water to become corrosive. Therefore, 350 ppm is the ideal target to ensure the longevity and proper functioning of plaster pool surfaces.

The correct answer is TDS, CYA (cyanuric acid), and borate. These three parameters are important for maintaining the water balance in a pool or spa. TDS (Total Dissolved Solids) refers to the concentration of all dissolved substances in the water, including minerals, salts, and other impurities. CYA (cyanuric acid) is a stabilizer that helps protect chlorine from degradation due to sunlight. Borate is a pH buffer that helps stabilize the water's pH level. By monitoring and adjusting these parameters, the water can be kept in optimal condition for swimming or soaking.

The correct answer is 50 ppm. Borate is often added to pool water as a pH buffer and to prevent algae growth. A level of 50 ppm is considered optimal for pool water with no SWG, as it helps maintain the pH balance and inhibits the growth of algae. Higher levels of borate may not provide any additional benefits and can potentially lead to cloudy water or staining.

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Based on the information provided, the correct answer is to add 51 fl oz of muriatic acid and aerate the pool. This is determined by referring to the pH-Total Alkalinity Adjusting Charts in Chapter 10, Page 103, which provides guidance on adjusting pH levels based on the pool's total alkalinity. In this case, with a pH of 7.8 and a TA of 110 ppm, the recommended action is to add muriatic acid to lower the pH, and then aerate the pool to help balance the chemistry.

The correct answer is that the hydrogen made gasses off and the bubbles created cause turbulence which raises pH. When a pool is equipped with a saltwater chlorine generator (SWG), it produces hydrogen gas as a byproduct. This hydrogen gas then escapes into the air, causing turbulence and the formation of bubbles in the pool water. This turbulence and the presence of bubbles increase the pH of the water, making it more alkaline. Therefore, the pH of the pool water usually goes up with an SWG due to the gassing off of hydrogen and the resulting turbulence.

Using liquid chlorine or other hypochlorites will not raise the pH of the pool water. In fact, these chemicals tend to lower the pH levels. When added to the water, they release hydrogen ions, which decrease the pH and make the water more acidic. To increase the pH, other chemicals like soda ash or sodium bicarbonate need to be added.