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pH

The hydrogen ion concentration of a substance, a logarithmic scale, a measure of its acidity or alkalinity. A pH of 7 is neutral; anything below is acid and anything above is alkaline. ...

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A Dictionary of Biomedicine (2 ed.)

Reference type:
Subject Reference
Current Version:
2019

...pH A logarithmic scale (−log 10 [H + ]) of hydrogen ion concentration (which determines the acidity or alkalinity of an aqueous solution). Neutrality corresponds to pH 7, strong acids approach pH 0, strong alkalis pH...

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pH n.   Quick reference

A Dictionary of Nursing (8 ed.)

Reference type:
Subject Reference
Current Version:
2021
Subject:
Medicine and health
Length:
43 words

... n. a measure of the concentration of hydrogen ions in a solution, and therefore of its acidity or alkalinity. A pH of 7 indicates a neutral solution, a pH below 7 indicates acidity, and a pH in excess of 7 indicates...

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Concise Medical Dictionary (10 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Medicine and health, Clinical Medicine
Length:
42 words

... a measure of the concentration of hydrogen ions in a solution, and therefore of its acidity or alkalinity. A pH of 7 indicates a neutral solution, a pH below 7 indicates acidity, and a pH in excess of 7 indicates...

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A Dictionary of Ecology (5 ed.)

Reference type:
Subject Reference
Current Version:
2015

... A value on a scale 0–14 which gives a measure of the acidity or alkalinity of a medium. A neutral medium has a pH of 7, acidic media have pH values of less than 7, and alkaline media of more than 7. The lower the pH the more acidic is the medium, the higher the pH, the more alkaline. The pH value is the logarithm of the reciprocal of the hydrogen ion concentration, expressed in moles per litre (pH = log 10 l/H + ). Most pH values in natural systems lie in the range 4–9. Human blood has a pH of 7.4, ocean water 8.1–8.3, water in saline environments may have a...

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A Dictionary of Plant Sciences (4 ed.)

Reference type:
Subject Reference
Current Version:
2019
Subject:
Science and technology, Life Sciences
Length:
76 words

... A value on a scale 0–14 that gives a measure of the acidity or alkalinity of a medium. A neutral medium has a pH of 7. Acidic media have pH values of less than 7, and alkaline media of more than 7. The lower the pH, the more acidic is the medium; the higher the pH, the more alkaline. The pH value is the reciprocal of the hydrogen ion concentration expressed in moles per...

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A Dictionary of Zoology (5 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Science and technology, Life Sciences
Length:
76 words

... A value on a scale 0–14 that gives a measure of the acidity or alkalinity of a medium. A neutral medium has a pH of 7; acidic media have pH values of less than 7, and alkaline media of more than 7. The lower the pH, the more acidic is the medium; the higher the pH, the more alkaline. The pH value is the reciprocal of the hydrogen ion concentration, expressed in moles per...

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A Dictionary of Psychology (4 ed.)

Reference type:
Subject Reference
Current Version:
2015

... abbrev . A measure of the acidity/alkalinity of a solution, originally the logarithm to the base 10 of the reciprocal of the concentration of hydrogen ions in moles per cubic decimetre, now indexed to a standard solution of potassium hydrogen phthalate at 15°C, which has a pH of 4 by definition. Acid ( 1 ) solutions have pH less than 7, pure water pH equal to 7, and alkaline solutions have pH more than 7. [Abbreviation of potential of hydrogen...

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A Dictionary of Dentistry (2 ed.)

Reference type:
Subject Reference
Current Version:
2020
Subject:
Medicine and health, Dentistry
Length:
40 words

...pH A measure of the acidity or alkalinity of a solution. A pH of 7.0 is neutral; greater than 7.0 is more basic; less than 7.0 is more acidic (the normal resting pH of saliva varies between 6.2 and...

pH

pH   Reference library

Oxford Dictionary of Biochemistry and Molecular Biology (2 ed.)

Reference type:
Subject Reference
Current Version:
2008
Subject:
Science and technology, Life Sciences
Length:
261 words

... a dimensionless quantity notionally defined as the negative decadic logarithm of the molal activity of hydrogen ions in a solution. Since the activity of a single species of ion is not measurable, pH is defined operationally according to the equation: pH ( X ) = pH ( S ) + ( E s − E x ) F / ( R T ln 10 ) where pH(S) and pH(X) are the pH values of a standard solution, S, and of the test solution, X, respectively; F is the Faraday constant, R the gas constant, and T the thermodynamic temperature; and E s and E x are, respectively, the electromotive...

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World Encyclopedia

Reference type:
Subject Reference
Current Version:
2004
Subject:
Encyclopedias
Length:
53 words

... Numerical scale that indicates the acidity or alkalinity of a solution. The pH value measures the concentration of hydrogen ions. The scale (introduced in 1909 ) runs from 0 to 14. A solution is acidic if the pH is less than 7 and alkaline if greater than 7. See also acid ; alkali ; ...

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Graham Saxby

The Oxford Companion to the Photograph

Reference type:
Subject Reference
Current Version:
2006
Subject:
Art & Architecture
Length:
228 words

... . The pH of a solution is a measure of its acidity or alkalinity. It is important in photographic processing. For example, the pH of a developer determines its level of activity; and the final pH of a paper print has a profound effect on its longevity. A neutral solution has a pH of 7.0; higher figures are associated with alkalinity, lower figures with acidity. The acidity of a solution depends on its hydrogen‐ion concentration, which is equal to the hydroxyl‐ion concentration (10 -7 moles per litre, hence the 7) in a neutral solution. The pH scale is...

pH

pH   Reference library

The Oxford Companion to the Body

Reference type:
Subject Reference
Current Version:
2003
Subject:
Science and technology, Life Sciences
Length:
96 words

... The negative logarithm of the hydrogen ion concentration [H + ] in mols/litre. Lower pH therefore means greater acidity, and vice versa. Extracellular fluid (ECF), including the blood, is normally at a pH close to 7.4 which means [H + ] = 10 -7.4 mols/litre, or 40 nanomoles/litre. At body temperature, neutral pH would be approximately 6.8; body fluids are therefore on the alkaline side of neutral. Control mechanisms normally keep ECF pH within 0.04 of the norm either way. The pH inside cells is more acid, and more variable, related to metabolic activity....

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A Dictionary of Public Health (2 ed.)

Reference type:
Subject Reference
Current Version:
2018

...pH The hydrogen ion concentration of a substance, a logarithmic scale, a measure of its acidity or alkalinity. A pH of 7 is neutral; anything below is acid and anything above is alkaline. ...

pH*

pH*   Reference library

Oxford Dictionary of Biochemistry and Molecular Biology (2 ed.)

Reference type:
Subject Reference
Current Version:
2008
Subject:
Science and technology, Life Sciences
Length:
33 words

...* a notation commonly used to denote the apparent pH of a solution containing 2 H 2 O (i.e. D 2 O), as measured electrometrically using a glass electrode without correction for the isotope effect on the...

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The Oxford Dictionary of Sports Science & Medicine (3 ed.)

Reference type:
Subject Reference
Current Version:
2007

... A measure of the relative acidity or alkalinity of a solution, the negative 1og 10 of the hydrogen ion concentration. A pH of 7 indicates neutrality, values above 7 indicate alkalinity, and those below 7 indicate...

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A Dictionary of Geology and Earth Sciences (5 ed.)

Reference type:
Subject Reference
Current Version:
2020

... The negative logarithm of the hydrogen ion concentration in a solution, pH = log 10 1/H + . If the hydrogen ion concentration of a solution increases, as happens with increasing acidity, the pH will decrease, and vice versa. The pH is measured on a scale of 0–14; a neutral medium (such as pure water) has a pH of 7.0, numbers above 7.0 indicate relative alkalinity, numbers below 7.0 indicate relative acidity. Most pH values in natural systems lie in the range 4.0–9.0. Human blood has a pH of 7.4, ocean water 8.1–8.3, water in saline environments may have a ...

pH

pH   Reference library

Horst Dornbusch

The Oxford Companion to Beer

Reference type:
Subject Reference
Current Version:
2013

...for pH neutrality. All acids, therefore, have a pH value of 0 to 7; all bases have a pH value of 7 to 14. An extremely acidic solution with a pH value of 1, for instance, has a 10 times greater concentration of hydrogen ions than a solution with a pH value of 2; it is 100 times more acidic than a solution with a pH value of 3, and so on. On the alkaline side, a base with a pH value of 10 is 10 times more caustic than a solution with a pH value of 9 and 100 times more caustic than one with a pH value of 8. The most common ways of measuring pH values are...

pH

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Robert White and Matt Thomson

The Oxford Companion to Wine (5 ed.)

Reference type:
Subject Reference
Current Version:
2023

..., generally have acid pH values, whereas those formed on basic parent materials, such as limestone , basalt , or dolerite, generally have alkaline pH values. The optimum pH range for grapevines is from 5.5 to 8 (in water) and approximately 0.6–0.8 units lower in calcium chloride solution. Within this range, the possibility of aluminium toxicity (at low pH) or micronutrient deficiency (at high pH) is avoided. However, grapevines are tolerant of soil pH outside this range. There is no evidence of a direct link between soil pH and wine pH. See also soil...

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A Dictionary of Agriculture and Land Management

Reference type:
Subject Reference
Current Version:
2019
Subject:
Social sciences
Length:
125 words

... A measure of the acidity or alkalinity of an aqueous solution on a scale of 0–14. Pure water has a pH of 7, which is neutral, with a reading below being acidic, and above being alkaline. When applied to soils , plants can grow within a range, some thriving in slightly more acidic conditions than others, but most thrive in pH 5–7. Outside this range, nutrients become unavailable to the plant; for example, calcium and magnesium in acid soils, and manganese, copper, zinc, and cobalt in alkaline soils. High levels of organic matter tend to have a lower pH, so...

pH

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The Oxford Companion to Spirits and Cocktails

Reference type:
Subject Reference
Current Version:
2021

...pH scale, each unit of change represents a tenfold change in acidity or alkalinity, so that the difference between a pH of 6.9 and 7 represents a one-point difference (not one-tenth of a point), measured in hydrogen ions by moles per liter. Thus a beverage that has a pH of 4 can be seen as crisp or tangy while a beverage with a pH of 3 can be frighteningly tart for many people. Solutions with very low pH can damage human tissue. Pure ethanol is slightly alkaline, with a pH of 7.33. While commercial spirits vary in their pH level, in general a well-made,...

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