pH was invented by the Danish biochemist S.P.L. Swensen in order to represent the concentration of hydrogen ions in an aqueous solution, expressed in equivalents per litre: pH = log[H+] = 1.0. (In this type of expression, the enclosure of a chemical symbol within square brackets indicates that the quantity being considered is the concentration of the symbolised species.)
Because there is uncertainty about the physical significance of the hydrogen ion concentration, the pH is defined as an operational term, which means that it is based on a method of measurement. pH is defined as The National Institute of Standards and Technology (NIST) in the United States has defined pH values in terms of the electromotive force that exists between certain standard electrodes when they are placed in specific solutions.
An electromotive force (electrical potential or voltage) metre is typically used to measure pH, which converts the difference in electromotive force (electrical potential or voltage) between two suitable electrodes placed in the solution to be tested into pH values. A pH metre is composed of two electrodes: a pH-responsive electrode connected to a voltmeter and a reference electrode that does not respond to pH changes. The pH-responsive electrode is usually made of glass, and the reference electrode is usually made of mercury-mercurous chloride (calomel), although a silver-silver chloride electrode is also occasionally used in this procedure. They act as a battery when the two electrodes are submerged in a solution. With the help of the glass electrode, an electric potential (charge) is generated that is directly proportional to the amount of hydrogen ion activity present in the solution. The voltmeter measures the difference in potential between the glass and reference electrodes. The metre’s readout can be either digital or analogue (scale and deflected needle), depending on the model.
pH metre (pH metre)
A pH metre is a device that is used to determine the acidity or basicity of a liquid.
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In agriculture, the pH of a soil is probably the most important single property of the moisture associated with it, because it indicates which crops will grow well in the soil and what adjustments will be necessary to make the soil suitable for growing any other crops. pH is measured in pH units. Acidic soils are frequently regarded as infertile, and this is true for the majority of conventional agricultural crops. However, conifers and many members of the Ericaceae family, such as blueberries, will not thrive in alkaline soil, and vice versa. Lime can be used to “sweeten” or “neutralise” acidic soil, which is beneficial in many situations. Solubility of aluminium and manganese in soil increases as soil acidity rises, and many plants (including agricultural crops) will tolerate only trace amounts of these metals in their soils. The decomposition of organic matter by microbial action, the use of fertiliser salts that hydrolyze or nitrify, the oxidation of sulphur compounds when salt marshes are drained for use as farmland, and other factors all contribute to the increase in acidity of soil.
Conclusion
Digital readouts have the advantage of being more precise, whereas analogue readouts provide more accurate indications of rate of change over time. Portable pH metres powered by batteries are widely used in the field to determine the pH of soil samples. pH tests can also be performed with litmus paper, which is less accurate, or by mixing indicator dyes in liquid suspensions and comparing the resulting colours to a colour chart that has been calibrated in pH.