As we all remember from the school chemistry course, pH is a unit of activity of a hydrogen ion equal to the inverse logarithm of the activity of hydrogen ions. Thus, water with a pH of 7 has 10 -7 mol per liter of hydrogen ions, and water with a pH of 6 is 10 -6 mol per liter. The pH scale can vary from 0 to 14.
In general, water with a pH less than 7 is considered acidic, and with a pH greater than 7 - alkaline. The normal pH range for surface water systems is from 6.5 to 8.5, and for underground systems is from 6 to 8.5.
The pH value of water (H 2 0) is 7 at 25 ° C, but when in contact with carbon dioxide in the atmosphere, this equilibrium shifts to a pH of approximately 5.2. Due to the close relationship between pH and atmospheric gases and temperature, it is highly recommended that water be tested as quickly 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 an aquifer, plumbing and pipelines, can penetrate into 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 characteristic "blue-green" staining of the sink and drains.
The main way to solve the problem of low pH of water is to use a neutralizer. It feeds the solution into the water to prevent the reaction of the water with the domestic plumbing or electrolytic corrosion. A typical neutralizer is chemical soda ash. Neutralization with this agent increases the sodium content in water.
Hard water
Water with a pH above 8.5 is hard. It does not pose a health hazard, but can cause aesthetic problems. These issues include:
- Formation of a “scale” or precipitate on pipelines and fixtures.
- Alkaline taste in water, which can make coffee taste bitter.
- Scale formation on dishes, washing machines, pools.
- Difficulty in obtaining foam from soap and detergents and the formation of insoluble precipitation on clothing, etc.
- Decrease in efficiency of electric water heaters.
Typically, these problems occur when stiffness ranges from 100 to 200 milligrams of CaCO 3 / L, which is equivalent to 12 grams per gallon. Water can be softened by using ion exchange or by adding ash, a soda-lime mixture, but both processes increase the sodium content in the water.
PH drinking water
Close attention to pH control is necessary at all stages of water treatment to ensure satisfactory quality and disinfection of water. Although the pH of water usually has no direct effect on consumers, it is one of the most important operational parameters of 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 its taste, smell and appearance.
The optimal pH 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 may result from 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 value of about 200mV-300mV (and in no case higher than 400mV).
PH of pool water
As mentioned above, pH is the most important characteristic not only for drinking water, but also for swimming pools, since chlorination is still mainly used for water disinfection, and when using chlorine, the effectiveness of disinfection strongly depends on the initial pH value of water.
Chlorine is the main disinfectant to prevent the development of infections in public pools, but chlorine also reacts with organic substances in water and forms disinfection by-products (PPDs): organic substances - a derivative of humic substances resulting from the interaction of water with sweat, urine, hair, skin cells and the remnants of personal hygiene products falling into the water from swimmers. The PPD content can be measured as the sum of all halogenated compounds. Some DAAs increase the risk of asthma, are carcinogens, or irritate the eyes and skin.
Chlorine is the common name for chlorous acid, which forms chlorine gas that 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, killing bacteria, cysts, spores and inactive viral. Thus, if the pH value in the swimming pool is at the lower level of the adjustable range, less chlorine must be obtained for the same degree of disinfection, and therefore, less potentially dangerous PPDs are formed in the water. As shown by numerous studies, the optimal pH level of water in the pool is in the range from 7.5 to 8.0. With a decrease in pH of only 1-0.5 units (up to 7.0-6.5), the level of PPD increases significantly, which is also genotoxic.
PH Methods
The pH scale is a logarithmic scale, which means that each increase or decrease by 1 unit represents a change with a factor of 10. For example, a solution with pH 11 is 10 times more alkaline than a solution with pH 10. There are several methods for determining the pH of water .
Determination of pH using test strips
Test strips are litmus test papers that react by changing color to pH fluctuations. You can buy them at pet stores, because 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).
Upon contact with water, the color of the test strip will change. You just have to compare the final color with the sample color scale on the package and get a specific value. This method of determining pH is fast, simple, cheap, but has a rather large error.
Rottinger litmus paper
Purchase litmus papers in the medical equipment stores of your city. After analyzing various ph tests (from cheap Chinese to expensive Dutch), we came to the conclusion that German ph Rottinger strips give the minimum error in the reading. The package contains an indicator scale from 1 to 14 (the maximum available interval!) And 80 ph strips, which are enough for a long time. Using these strips, you can measure not only ph of water, but also ph of such biological fluids as saliva, urine, etc. Since good ph meters are quite expensive (about 3000 rubles), and you have to buy buffer solutions for calibration for them, the Rottinger litmus paper, the price of which does not exceed 250-350 rubles, will serve as an indispensable assistant in accurately determining the level of ph.
Determination of pH using a pH meter
A sample of water (20-30 ml) is taken in a plastic or glass cup. The sensor of the device is rinsed with a small amount of distilled water, and then immersed in a solution with a temperature sensor. The instrument scale shows you the exact pH value of the test solution. It should be borne in mind that the accuracy of measurements is affected by the regular calibration of the device, for which standard solutions with a known pH value are used. This method of determining pH is accurate, simple, fast, but requires large material costs compared to the previous and 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 should be monitored to avoid problems with equipment and health.