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pH value is used to measure the acidic or basic nature of aqueous or other liquid solutions. It is a frequently used word in chemistry, biology, and agronomy. Hydrogen and hydroxyl ion activity in solution 1 to 10?14 gram-equivalents per liter, measured into pH scale having values between 0 and 14. The hydrogen ion concentration of pure water has pH 7, which indicates that it is neutral (neither acidic nor alkaline), and it has a concentration of hydrogen 7-10 gram-equivalents per liter. Solutions with a pH of less than 7 are acidic, while others with a pH of greater than 7 are basic or alkaline.


S.P.L. Srensen, a Danish biochemist, first employed the pH measurement to describe the hydrogen ion concentration of an aqueous solution in equivalents per liter:

pH = log[H+].

The value of PH is totally based on measuring. The physical Importance of the hydrogen ion concentration is unspecified. That's why pH is defined operationally. In solutions, electromotive force exists between specific standard electrodes. According to the National Institute of Standards and Technology, the solution's electromotive force between specific electrodes characterizes pH values.

A pH meter determines pH value by putting it in a solution to be tested. The difference of electromotive force (electrical potential or voltage) between reference electrodes determines the pH of the solution. A voltmeter is connected to a pH-responsive electrode and a reference electrode in a pH meter. The pH-responsive electrode is often made of glass, whereas the reference electrode is typically composed of mercury-mercurous chloride (calomel); however, a silver-silver chloride electrode is occasionally employed. When immersed in a solution, the two electrodes act as a battery. The voltmeter measures the potential difference between the glass and reference electrodes. The glass electrode of the voltmeter generates an electric potential proportional to the number of hydrogen ions in the solution. The meter reads in digital or analog mode (scale and deflected needle). Although digital readouts are more exact, analog readouts provide better signals of rate changes. In the fields, portable pH meters with batteries are routinely used to measure the pH of soils. Litmus paper or mixing indicator dyes are used in liquid suspensions. Comparing the resulting colors to a pH-calibrated color chart can also measure pH, but both procedures are less accurate.

Measuring pH

The electrode method, the colorimetric approach, and the hydrion paper method are used to measure pH values. A probe and meter used in the electrode are the most common and also the most accurate method. The meter detects small voltage changes between the reference and measuring electrodes. This voltage is converted to a millivolt (mV) pH measurement.

In the colorimetric approach, indicator chemicals such as bromthymol blue and phenol red are employed to produce color in the solution - red for acid and blue for base. The liquid's color and intensity are then compared to a set of color criteria. For the hydrion technique, a particular test paper (litmus paper) is dipped into the solution. The color produced on the paper is then compared to color standards. Acids cause litmus paper to turn red, while bases cause it to turn blue.

When used with a properly calibrated meter and a fresh sample, the electrode gives reliable results. Most meters can be calibrated using one of three common pH buffers. Typically, pH buffers of 4, 7, and 10 are utilized. After being calibrated using these buffers, the meter is considered accurate over a wide range of pH values.

The Importance of pH

The pH has characteristics to verify water's solubility and biological availability of chemical components, such as nutrients (phosphorus, nitrogen, and carbon) and heavy metals (lead, copper, cadmium, etc.). pH can also be used to determine the amount and type of phosphorus present in the water and utilize it for aquatic life. In the case of heavy metals, their toxicity is determined by how soluble they are. Because metals that are more soluble at lower pH, are more hazardous.

Acids and bases have different properties.

1. Acidic Properties

Acids are naturally corrosive.

They are excellent electrical conductors.

The pH of urine is always less than 7.

Acidic chemicals produce hydrogen gas when they react with metals.

Acids have a sour taste.

Sulfuric acid [H2SO4], hydrochloric acid [HCl], and acetic acid [CH3COOH] are some of the examples of Acidic chemicals.

2. Base Characteristics

All bases hold some common traits, such as a bitter taste. The bases are also slick. Furthermore, bases conduct electricity when submerged in water because they include charged particles in the solution.

They have a soapy texture when they are touched.

When these chemicals are dissolved in water, they produce hydroxide ions (OH- ions).

Bases are good conductors of electricity in their aqueous solutions.

The pH values of the bases are always higher than 7.

Bases are bitter-tasting chemicals and can turn red litmus paper blue.

Sodium hydroxide [NaOH], milk of magnesia [Mg(OH)2], and calcium hydroxide [Ca(OH)2] are some of the examples of bases.

3. Substances that are neither acidic nor alkaline

The neutral substances that have neither acidic nor basic properties have the same quantity of hydrogen and hydroxyl ions as the litmus surface. These substances do not change the color of the litmus surface.

There are no acidic or basic properties in these compounds.

Their pH levels are 7, or close to 7.

On red or blue litmus paper, neutral compounds have no impact.

Pure water has a pH of exactly 7.

Water and common salt are two examples (NaCl).

pH of soil

The soil pH is perhaps a single essential attribute of the moisture linked with it in agriculture because it indicates which crops will grow well in the soil and what alterations must be done to adapt it for growing other crops. Acidic soils are commonly infertile. Conifers and many Ericaceae plants, such as blueberries, will not survive in alkaline soil. It can be "sweetened" or neutralized by treating acidic soil with lime. Aluminum and manganese become more soluble in the soil when soil acidity rises, and many plants (including agricultural crops) can only tolerate small amounts of those metals. The acidity of the soil is increased as a result of the decomposition of organic matter by microbial action, fertilizer salts that hydrolyze or nitrify, oxidation of sulfur compounds when salt marshes are drained to use as farmland, and many other factors.

What does a normal blood pH look like?

The pH of blood should be between 7.35 and 7.45. This suggests that blood is slightly alkaline or basic by nature. And stomach acid, on the other hand, has a pH of 1.5 to 3.5, which indicates its acidic nature. A low pH is beneficial for digestion and the destruction of any microorganisms that enter the stomach. Acidosis occurs when blood pH falls below 7.35 and becomes too acidic. However, alkalosis occurs when blood pH rises above 7.45 and becomes too alkaline. The two primary organs that aid in blood pH equilibrium are:

Lungs eliminate carbon dioxide from the body through breathing or respiration.

And, Kidney, acid is removed from this organ through urine or excretion.

Drinking water's PH

Weather trends, human activities, and natural processes all influence freshwater pH around the world.

Chemical or heavy metal pollution can cause water to have a very low or high pH.

Water that isn't in the "safe" pH range of 6.5 to 8.5, especially if it's alkaline, isn't always dangerous.

On the other hand, very acidic water might have a disagreeable odor or flavor and damage pipes and water-carrying appliances.

Water with a pH of less than 6.5 is more likely to be polluted, making it dangerous to drink. Metal pipes can also be corroded by it.

What role does pH play in the canning of foods?

Foods are categorized as "acid foods" (low pH; pH of 4.6 or lower) or "low-acid foods" (pH of 4.6 or higher). The pH of the foods determines the safe canning method. Fruits and pickles that are acidic are carefully preserved in a boiling water bath canner. It is done because the combination of acid of pickle and boiling water (212°F) kills harmful microbes like acid-tolerant molds and yeast. The killing of these microbes is necessary because the presence of these microbes can increase ph. Along with boiling water, lemon juice or citric acid is also added before processing in a bath canner as pH values of items like figs and tomatoes are also slightly above 4.6. It is important to process low-acid items like vegetables and meats in a pressure canner to preserve food.

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