As we all remember from the school chemistry course, pH is a unit of hydrogen ion activity, equal to the reciprocal logarithm of hydrogen ion activity. Thus, water with a pH of 7 has 10-7 moles per liter of hydrogen ions, and water with a pH of 6 has 10-6 moles per litre. The pH scale can range from 0 to 14.
In general, water with a pH less than 7 is considered acidic, while water with a pH greater than 7 is considered alkaline. The normal pH range for surface water systems is 6.5 to 8.5 and for underground systems is 6 to 8.5.
The pH value of water (H20) is 7 at 25°C, but upon contact with carbon dioxide in the atmosphere, this equilibrium shifts to a pH of approximately 5.2. - due to the close relation of pH to atmospheric gases and temperature, it is highly recommended that the water be tested as soon as possible. After all, the pH of water is not a measure of the stability of an acidic or alkaline reaction and does not give a complete picture of the characteristics or reason for limiting water supply.
Soft water
In general, low pH water (less than 6.5)is acidic, soft and corrosive. Thus, metal ions such as iron, manganese, copper, lead and zinc from the aquifer, plumbing and pipelines can penetrate into the water. Therefore, low pH water can:
- contain elevated levels of toxic metals;
- lead to premature damage to metal pipes;
- have a metallic or sour taste;
- dye linen;
- have a distinctive "blue-green" coloration of sinks and drains.
The main way to solve the problem of low pH water is to use a neutralizer. It feeds the solution into the water to prevent water from reacting with domestic plumbing or electrolytic corrosion. A typical neutralizer is chemical soda ash. Neutralization with this agent increases the sodium content of the water.
Hard water
Water with a pH above 8.5 is hard. It does not pose a he alth hazard, but may cause aesthetic problems. These issues include:
- Formation of "scale" or sediment on pipelines and fixtures.
- Alkaline taste in water that can make coffee taste bitter.
- Calculation on dishes, washing machine, pools.
- Difficulty in obtaining foam from soaps and detergents and the formation of insoluble residues on clothes, etc.
- Reducing the efficiency of electric water heaters.
Typically, these problems occur when the hardness varies within100 to 200 milligrams CaCO3/L, equivalent to 12 grams per gallon. Water can be softened by using ion exchange or by adding ash, lime and soda, but both processes increase the sodium content of the water.
PH drinking water
Careful attention to pH control is necessary at all stages of water treatment to ensure satisfactory water quality and disinfection. Although water pH does not usually have a direct impact on consumers, it is one of the most important performance parameters for water quality. For effective disinfection with chlorine, the pH should preferably be less than 8. The pH of the water entering the distribution system must be controlled to minimize pipe corrosion. Failure to do so may result in contamination of drinking water and adverse effects on taste, odor and appearance.
The optimum pH value will vary for different materials depending on the composition of the water and the nature of the building materials used in the distribution system, but most often it lies in the range of 6.5-9.5. Extreme pH values can be the result of accidental spills, breakdowns at wastewater treatment plants.
The ideal pH level of ionized water for long-term human consumption is between 8.5 and 9.5 (and never exceeds 10.0) with an ideal ORP of around 200mV-300mV (and never above 400mV).
PH of pool water
As alreadyAs mentioned above, pH is an important characteristic not only for drinking water, but also for swimming pools, since chlorination is still mainly used to disinfect water, and when using chlorine, the effectiveness of disinfection is highly dependent on the initial pH value of the water.
Chlorine is the main disinfecting agent for preventing infections in public pools, but chlorine also reacts with organic matter in the water to form disinfection by-products (DBPs): organic matter is a derivative of humic substances produced by the interaction of water with sweat, urine, hair, skin cells and personal care products that enter the water from swimmers. The content of PPD can be measured as the sum of all halogenated compounds. Some DAAs increase the risk of asthma, are carcinogenic, or irritate the eyes and skin.
Chlorine is the generic name for chlorous acid, which forms chlorine gas when it reacts with water. Dissolving in water, the acid forms hypochlorite and has a pKa value of 7.5.
Chloric acid is much more effective than hypochlorite at killing bacteria, cysts, spores and inactive viruses. Thus, if the pH value of the swimming pool is at the lower end of the regulated range, less chlorine needs to be produced for the same degree of disinfection, and consequently, less potentially dangerous RCPs are formed in the water. As shown by numerous studies, the optimal pH level of water in the pool lies in the range from 7.5 to 8.0.by only 1-0.5 units (up to 7.0-6.5) the level of DAAs significantly increases, which are also genotoxic.
Methods for determining pH
The pH scale is a logarithmic scale, which means that every 1 unit increase or decrease represents a change by a factor of 10. For example, a pH 11 solution is 10 times more alkaline than a pH 10 solution. There are several methods how to determine the pH of water.
Determination of pH with test strips
Test strips are litmus paper that reacts by changing color to pH fluctuations. You can buy them at pet stores, as they are often used to determine the pH of water in aquariums (even a slight fluctuation in this indicator can lead to the death of fish).
When in contact with water, the color of the test strip will change. You only have to compare the final color with the sample color chart on the package and get a specific value. This method for determining pH is fast, simple, cheap, but has a fairly large error.
Rottinger Litmus Paper
Purchase litmus papers in medical equipment stores in your city. After analyzing various ph tests (from cheap Chinese to expensive Dutch), we came to the conclusion that the German Rottinger ph strips give the minimum error in the reading. The package comes with an indicator scale from 1 to 14 (the maximum available interval!) And 80 ph strips, which are enough for a long time. With the help of datastrips can measure not only the ph of water, but also the ph of biological fluids such as saliva, urine, etc. Since good ph meters are quite expensive (about 3000 rubles), and you have to buy buffer solutions for calibration, then Rottinger litmus paper, the price of which does not exceed 250-350 rubles, will serve as an indispensable assistant in accurately determining the ph level.
Determination of pH with a pH meter
A water sample (20-30 ml) is taken into a plastic or glass cup. The sensor of the device is rinsed with a small amount of distilled water, and then immersed in the solution together with the temperature sensor. The instrument's scale shows you the exact pH value of the test solution. In this case, it should be taken into account that the accuracy of measurements is affected by regular calibration of the instrument, for which standard solutions with a known pH value are used. This method for determining pH is accurate, simple, fast, but requires more material costs than the previous one and the simplest skills in working with laboratory equipment and chemical solutions.
Thus, the pH of water is not just a term from a school chemistry course, but also an indicator of water quality that must be monitored to avoid problems with equipment and he alth.
