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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]
The pH value of a neutral solution is 7.0 at 25°C (standard laboratory conditions). Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic. Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic.
The optimum pH range for most plants is between 5.5 and 7.5; [3] however, many plants have adapted to thrive at pH values outside this range. Classification of soil pH ranges [ edit ]
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]
In this case H 0 and H − are equivalent to pH values determined by the buffer equation or Henderson-Hasselbalch equation. However, an H 0 value of −21 (a 25% solution of SbF 5 in HSO 3 F) [5] does not imply a hydrogen ion concentration of 10 21 mol/dm 3: such a "solution" would have a density more than a hundred times greater than a neutron ...
On this scale, pure H 2 SO 4 (18.4 M) has a H 0 value of −12, and pyrosulfuric acid has H 0 ~ −15. [7] Take note that the Hammett acidity function clearly avoids water in its equation. It is a generalization of the pH scale—in a dilute aqueous solution (where B is H 2 O), pH is very nearly equal to H 0.
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More precise measurements sometimes require calibration at three different pH values. Some pH meters provide built-in temperature-coefficient correction, with temperature thermocouples in the electrode probes. The calibration process correlates the voltage produced by the probe (approximately 0.06 volts per pH unit) with the pH scale.
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