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Soil pH is a key characteristic that can be used to make informative analysis both qualitative and quantitatively regarding soil characteristics. [ 1] pH is defined as the negative logarithm (base 10) of the activity of hydronium ions ( H+. or, more precisely, H. 3O+. aq) in a solution.
The pH range is commonly given as zero to 14, but a pH value can be less than 0 for very concentrated strong acids or greater than 14 for very concentrated strong bases. [ 2 ] The pH scale is traceable to a set of standard solutions whose pH is established by international agreement. [ 3 ]
Values are at 25 °C and 0 ionic strength. The pK a values are the pH values where the concentration of each species is equal to that of its conjugate bases. At pH 1 or lower, the phosphoric acid is practically undissociated. Around pH 4.7 (mid-way between the first two pK a values) the dihydrogen phosphate ion, [H 2 PO 4] −
A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH ( acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. [ 1] Hence, a pH indicator is a chemical detector for hydronium ions (H 3 O +) or hydrogen ions (H +) in the ...
Phenyl group. In organic chemistry, the phenyl group, or phenyl ring, is a cyclic group of atoms with the formula C6H5, and is often represented by the symbol Ph (archaically φ ). The phenyl group is closely related to benzene and can be viewed as a benzene ring, minus a hydrogen, which may be replaced by some other element or compound to ...
Universal indicator. A universal indicator is a pH indicator made of a solution of several compounds that exhibit various smooth colour changes over a wide range pH values to indicate the acidity or alkalinity of solutions. A universal indicator can be in paper form or present in a form of a solution. [ 1]
Phenolphthalein ( / fɛˈnɒl ( f) θəliːn / [citation needed] feh-NOL (F)-thə-leen) is a chemical compound with the formula C 20 H 14 O 4 and is often written as " HIn ", " HPh ", " phph " or simply " Ph " in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless ...
At pH = 7, when [ H +] = 10 −7 M, the reduction potential of H + differs from zero because it depends on pH. Solving the Nernst equation for the half-reaction of reduction of two protons into hydrogen gas gives: 2 H+ + 2 e− ⇌ H2. In biochemistry and in biological fluids, at pH = 7, it is thus important to note that the reduction potential ...