As we all remember from school chemistry course, pH - a unit of the hydrogen ion activity is equal to the inverse logarithm of the hydrogen ion activity.Thus, water having a pH equal to 7 is 10-7 moles per liter of hydrogen ions, and water of pH 6 - 10-6 moles per liter.Scale pH can vary in the range from 0 to 14.
Generally water with a pH of less than 7 is considered acidic, with a pH greater than 7 - alkaline.The normal pH range for surface water systems ranges from 6.5 to 8.5, and for underground systems - from 6 to 8.5.
The pH of water (H20) is equal to 7 at 25 ° C, but in contact with the carbon dioxide in the atmosphere, this equilibrium shifts to pH - about 5.2.Because of the close connection with atmospheric gases, pH, and temperature it is strongly recommended that the water was tested as soon as possible.After pH of the water is not a measure of the stability of the acid or alkaline reaction, and does not give a complete picture of the characteristics or grounds for restricting supply.
Soft water
Overall water with low pH (less than 6.5) is acidic, soft and corrosive.Thus, water may penetrate the metal ions such as iron, manganese, copper, lead and zinc from the aquifer and plumbing pipes.Therefore, water with a low pH can:
- contain elevated levels of toxic metals;
- cause premature damage to the metal pipe;
- have a metallic or sour taste;
- painted underwear;
- have the characteristic "blue-green" staining of sinks and drains.
main way to solve the problem of the low pH of the water is to use a converter.It delivers the solution into the water to prevent the reaction of water with the domestic water supply or electrolytic corrosion.A typical converter - chemical soda ash.Neutralization of this facility increases the sodium content in the water.
Hard water
Water with a pH above 8.5 is fierce.It is not harmful to health, but can cause aesthetic problems.These problems include:
- Formation "scale" or residue on pipes and fixtures.
- alkaline taste of water, which can make coffee taste bitter.
- Scale formation on dishes, washing machine, pool.
- Difficulty in obtaining the foam of soap and detergents, and the formation of insoluble precipitates on clothing, and so on. D.
- decrease in the efficiency of electric water heaters.
Typically, these problems occur when the rigidity varies from 100 to 200 mg CaCO3 / liter, which is equivalent to 12 grams per gallon.Water may be softened by the use of ion exchange or addition of ash, soda-lime mixture, but the two processes increase the sodium content in the water.
PH drinking water
Careful attention to pH control is necessary at all stages of water treatment to ensure satisfactory quality and water disinfection.Although the pH of the water usually has no direct effect on consumers, it is one of the most important operational water quality parameters.For effective disinfection with chlorine the pH should be preferably less than 8. PH inlet water distribution system must be controlled to minimize corrosion of the pipes.Failure to do so may lead to contamination of drinking water and adverse consequences for its taste, smell and appearance.
optimum pH will vary for different materials, depending on the composition of the water and the nature of building materials used in the distribution system, but often it is in the range 6.5-9.5.Extreme pH values can result from accidental spills, breakdowns at treatment plants.
ideal pH level of ionized water for long-term human consumption is between 8.5 and 9.5 (and never more than 10.0) with an ideal ORP value of about 200mV-300mV (and in any case not higher than 400mV).
PH pool water
As mentioned above, pH - the most important characteristic not only for drinking water but also for swimming, since water disinfection is still mainly used chlorination, and the use of chlorine disinfection efficiency depends strongly on theinitial pH value of water.
Chloro the main disinfecting agent for the prevention of infection in public swimming pools, but also reacts with chlorine organic substances in the water and forms disinfection byproducts (PDP): organic matter - a derivative of humic substances formed by the interaction of water with sweat, urine,hair, skin cells, and the remnants of personal hygiene products that fall into the water by swimmers.Contents PDI can be measured as the sum of all halogenated compounds.Some PPD increase the risk of developing asthma, are carcinogenic or irritating to eyes and skin.
Chlorine is the general name of chlorous acid, which forms the chlorine gas reacts with the water.Dissolved in water, acid forms of hypochlorite and has a pKa value of 7.5.
chlorous acid is much more effective than hypochlorite, killing bacteria, cysts, spores, and inactive virus.Thus, if the pH value of the swimming pool is located at the bottom level of the control range, minimal amounts of chlorine are required for the same degree of disinfection, and hence less water gives a potentially hazardous PDP.As shown by numerous studies, the optimal pH of the water in the pool is in the range from 7.5 to 8.0.By reducing the pH by only 1-0,5 units (up to 7,0-6,5) significantly increased levels of PDI, which also still gennotoksichny.
Methods for determination of pH
pH scale is a logarithmic scale, which means that each increase or decrease of one unit represents a change by a factor of 10. For example, a solution with a pH of 11 to 10 times more alkaline thansolution at pH 10. There are several methods how to determine the pH value.
Determining pH using test strips
Test strips are a litmus paper, color change responsive to fluctuations in pH.You can buy them in pet stores, as they are often used to determine the pH of the water in aquariums (even a slight fluctuation of this indicator can lead to fish kills).
In contact with water the color of the test strip will change.You have only to compare the resulting color with the sample color chart on the packaging and get a specific value.This method of determining pH is fast, simple, cheap, but has a large error.
Determination of the pH with pH-meter
In a plastic cup or glass, a sample of the water (20-30 ml).The sensor device is rinsed with a small amount of distilled water, and then immersed in a solution together with the temperature sensor.The scale of the device shows you the exact value of the pH of the test solution.It should be borne in mind that the measurement accuracy affects the regular calibration of the instrument for which use standard solutions with a known quantity pH.This method of determining pH accurate, simple, fast, but require large material costs compared with the previous and the elementary skills of working with laboratory equipment and chemical solutions.
Thus, pH of water - is not just a term from the school chemistry course, but also an indicator of water quality that must be controlled in order to avoid any problems with equipment and health.
