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pH is a measure of the acidity or alkalinity of a solution. Aqueous solutions at 25°C with a pH less than seven are considered acidic, while those with a pH greater than seven are considered basic (alkaline). When a pH level is 7.0, it is defined as 'neutral' at 25°C because at this pH the concentration of H3O+ equals the concentration of OH in pure water. pH is formally dependent upon the activity of hydronium ions (H3O+),[1] but for very dilute solutions, the molarity of H3O+ may be used as a substitute with little loss of accuracy.[2] (H+ is often used as a synonym for H3O+.) Because pH is dependent on ionic activity, a property which cannot be measured easily or fully predicted theoretically, it is difficult to determine an accurate value for the pH of a solution. The pH reading of a solution is usually obtained by comparing unknown solutions to those of known pH, and there are several ways to do so. Look up PH, pH in Wiktionary, the free dictionary. ... For other uses, see Acid (disambiguation). ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... Acid-base extraction in chemistry is a procedure using sequential liquid-liquid extractions to purify amines and acids from mixtures based on their chemical properties. ... Acids and bases: Acid-base reaction pH Self-ionization of water Buffer solutions Systematic naming Acid-base extraction Acidity function Proton affinity Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit is a chemical reaction that... The acid dissociation constant (Ka), also known as the acidity constant or the acid-ionization constant, is a specific equilibrium constant for the reaction of an acid with its conjugate base in aqueous solution [1]. // When an acid dissolves in water, it partly dissociates forming hydronium ions and its conjugate... Acids and bases: Acid-base reaction pH Self-ionization of water Buffer solutions Systematic naming Acid-base extraction Acidity function Proton affinity Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit An acidity function is a... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit Buffer solutions are solutions which resist change... Acids and bases: Acid-base reaction pH Self-ionization of water Buffer solutions Systematic naming Acid-base extraction Acidity function Proton affinity Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit The proton affinity, Epa, of... The self-ionization of water is the chemical reaction in which two water molecules react to produce a hydronium (H3O+) and a hydroxide ion (OH-): The reaction is also known as the autoionization or autodissociation of water. ... For other uses, see Acid (disambiguation). ... In chemistry, a Lewis acid can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. ... Headline text Happy Hannukah and a happy new year!! POOP e Butt ... An organic acid is an organic compound that is an acid. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit A... A superacid is an acid with an acidity greater than that of 100% sulfuric acid. ... A weak acid is an acid that does not fully ionize in solution; that is, if the acid was represented by the general formula HA, then in aqueous solution a significant amount of undissolved HA still remains. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... A Lewis base is any molecule or ion that can form a new covalent bond by donating a pair of electrons. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Mineral acids Organic acids Bases: Strong bases Weak bases Organic bases edit An organic base is an organic compound which acts as a base. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... In chemistry, a superbase is an extremely strong base. ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit As... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit In chemistry, a weak base is a... For other uses, see Acid (disambiguation). ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... In chemistry, hydronium is the common name for the cation H3O+. // Nomenclature According to IUPAC ion nomenclature, it should be referred to as oxonium. ... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ... Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ... In chemistry, hydronium is the common name for the cation H3O+ derived from protonation of water. ... This article is about the electrically charged particle. ... For other uses, see Concentration (disambiguation). ...


The concept of pH was first introduced by Danish chemist S. P. L. Sørensen at the Carlsberg Laboratory[3] in 1909. The name, pH, has claimed to have come from any of several sources including: pondus hydrogenii, potentia hydrogenii (Latin),[4] potentiel hydrogène (French), and potential of hydrogen (English).[5] A chemist pours from a round-bottom flask. ... Søren Peder Lauritz Sørensen, born in Havrebjerg, Denmark on January 9, 1868 and died on February 12, 1939, was a Danish chemist. ... The Carlsberg Laboratory and in the foreground a statue of its founder J.C. Jacobsen. ... Year 1909 (MCMIX) was a common year starting on Friday (link will display full calendar) of the Gregorian calendar (or a common year starting on Thursday of the 13-day-slower Julian calendar). ... For other uses, see Latin (disambiguation). ... The English language is a West Germanic language that originates in England. ...

Contents

Definition

pH (potential of hydrogen) is defined[6] operationally as follows. For a solution X, first measure the electromotive force EX of the galvanic cell An operational definition of a quantity is the description of a specific process, or set of validation tests, accessible to more persons than the definer (i. ... Electromotive force (emf) is the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric field existing across that device. ... The Galvanic cell, named after Luigi Galvani, consists of two different metals connected by a salt bridge or a porous disk between the individual half-cells. ...

text{pH(X)} = text{pH(S)} + frac{(E_{text{S}} - E_{text{X}})F}{RT ln 10}

where

F is the Faraday constant;
R is the molar gas constant;
T is the thermodynamic temperature.

Defined this way, pH is a dimensionless quantity. Values pH(S) for a range of standard solutions S, along with further details, are given in the relevant IUPAC recommendation[7]. I am the man. ... Molar gas constant (also known as universal gas constant, usually denoted by symbol R) is the constant occurring in the universal gas equation, i. ... Thermodynamic temperature is the absolute measure of temperature and is one of the principal parameters of thermodynamics. ... In the physical sciences, a dimensionless number (or more precisely, a number with the dimensions of 1) is a quantity which describes a certain physical system and which is a pure number without any physical units; it does not change if one alters ones system of units of measurement... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ...


pH has no fundamental meaning as a unit; its official definition is a practical one. However in the restricted range of dilute aqueous solutions having an amount-of-dissolved-substance concentrations less than 0.1 mol/L, and being neither strongly alkaline nor strongly acidic (2 < pH < 12), the definition is such that The first solvation shell of a sodium ion dissolved in water An aqueous solution is a solution in which the solvent is water. ... The common (Arrhenius) definition of a base is a chemical compound that either donates hydroxide ions or absorbs hydrogen ions when dissolved in water. ... For alternative meanings see acid (disambiguation). ...

text{pH} = -log_{10}left[frac{gamma_1 [text{H}^+]) }{ text{1 mol L}^{-1} } right] pm 0.02

where [H+] denotes the amount-of-substance concentration of hydrogen ion H+ and γ1 denotes the activity coefficient of a typical univalent electrolyte in the solution. The Activity coefficient for chemicals in a mixture is an indicator of what the concentration of that chemical will be in a vapor of the mixture. ... The term univalent or monovalent describes atoms with one valence electron, i. ... An electrolyte is a substance containing free ions that behaves as an electrically conductive medium. ...


Explanation

Visual representation of the pH scale.
Visual representation of the pH scale.
Another visual representation of the pH scale.

In simpler terms, the number arises from a measure of the activity of hydrogen ions (or their equivalent) in the solution. The pH scale is an inverse logarithmic representation of hydrogen proton (H+) concentration. Unlike linear scales which have a constant relations between the item being measured (H+ concentration in this case) and the value reported, each individual pH unit is a factor of 10 different than the next higher or lower unit. For example, a change in pH from 2 to 3 represents a 10-fold decrease in H+ concentration, and a shift from 2 to 4 represents a one-hundred (10 × 10)-fold decrease in H+ concentration. The formula for calculating pH is: Image File history File links Size of this preview: 639 × 600 pixelsFull resolution (768 × 721 pixels, file size: 95 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 639 × 600 pixelsFull resolution (768 × 721 pixels, file size: 95 KB, MIME type: image/png) File historyClick on a date/time to view the file as it appeared at that time. ... Image File history File links Size of this preview: 800 × 200 pixelsFull resolution (1200 × 300 pixels, file size: 23 KB, MIME type: image/png) Another diagram of the pH scale. ... Image File history File links Size of this preview: 800 × 200 pixelsFull resolution (1200 × 300 pixels, file size: 23 KB, MIME type: image/png) Another diagram of the pH scale. ... Activity in chemistry is a measure of how different molecules in a non-ideal gas or solution interact with each other. ... This article is about the chemistry of hydrogen. ... Logarithms to various bases: is to base e, is to base , and is to base . ...

mbox{pH} = -log_{10} alpha_{mathrm{H}^+}

Where αH+ denotes the activity of H+ ions, and is dimensionless. In solutions containing other ions, activity and concentration will not generally be the same. Activity is a measure of the effective concentration of hydrogen ions, rather than the actual concentration; it includes the fact that other ions surrounding hydrogen ions will shield them and affect their ability to participate in chemical reactions. These other ions change the effective amount of hydrogen ion concentration in any process that involves H+. In dimensional analysis, a dimensionless number (or more precisely, a number with the dimensions of 1) is a pure number without any physical units. ...


In dilute solutions (such as tap water), activity is approximately equal to the numeric value of the concentration of the H+ ion, denoted as [H+] (or more accurately written, [H3O+]), measured in moles per litre (also known as molarity). Therefore, it is often convenient to define pH as: A water tap Tap water (also known as running water) has existed for as long as indoor plumbing, i. ... In chemistry, hydronium is the common name for the cation H3O+ derived from protonation of water. ... The mole (symbol: mol) is the SI base unit that measures an amount of substance. ... The litre or liter (see spelling differences) is a unit of volume. ... This page refers to concentration in the chemical sense. ...

mbox{pH} approx -log_{10}{frac{[mathrm{H^+}]}{1~mathrm{mol/L}}}

For both definitions, log10 denotes the base-10 logarithm, therefore pH defines a logarithmic scale of acidity. For example, if one makes a lemonade with a H+ concentration of 0.0050 moles per litre, its pH would be: Logarithms to various bases: is to base e, is to base , and is to base . ... A logarithmic scale is a scale of measurement that uses the logarithm of a physical quantity instead of the quantity itself. ... This article is about the drink made with lemons. ...

mbox{pH}_{mathrm{lemonade}} approx -log_{10}{(0.0050)} approx 2.3

A solution of pH = 8.2 will have an [H+] concentration of 10−8.2 mol/L, or about 6.31 × 10−9 mol/L. Thus, its hydrogen activity αH+ is around 6.31 × 10−9. A solution with an [H+] concentration of 4.5 × 10−4 mol/L will have a pH value of 3.35.


In solution at 25 °C, a pH of 7 indicates neutrality (i.e. the pH of pure water) because water naturally dissociates into H+ and OH ions with equal concentrations of 1×10−7 mol/L. A lower pH value (for example pH 3) indicates increasing strength of acidity, and a higher pH value (for example pH 11) indicates increasing strength of basicity. Note, however, that pure water, when exposed to the atmosphere, will take in carbon dioxide, some of which reacts with water to form carbonic acid and H+, thereby lowering the pH to about 5.7. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ... Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. ...


Neutral pH at 25 °C is not exactly 7. pH is an experimental value, so it has an associated error. Since the dissociation constant of water is (1.011 ± 0.005) × 10−14, pH of water at 25 °C would be 6.998 ± 0.001. The value is consistent, however, with neutral pH being 7.00 to two significant figures, which is near enough for most people to assume that it is exactly 7. The pH of water gets smaller with higher temperatures. For example, at 50 °C, pH of water is 6.55 ± 0.01. This means that a diluted solution is neutral at 50 °C when its pH is around 6.55 and that a pH of 7.00 is basic. In chemistry and biochemistry, a dissociation constant or an ionization constant is a specific type of equilibrium constant used for reversible reactions or processes. ... Significant figures (also called significant digits and abbreviated sig figs or sig digs, respectively) is a method of expressing errors in measurements. ...


Most substances have a pH in the range 0 to 14, although extremely acidic or extremely basic substances may have pH less than 0 or greater than 14. An example is acid mine runoff, with a pH = –3.6. Note that this does not translate to a molar concentration of 3981 M; such high activity values are the result of the extremely high value of the activity coefficient while concentrations are within a "reasonable" range [8]. E.g. a 7.622 molal H2SO4 solution has a pH = -3.13, hydrogen activity αH+ around 1350 and activity coefficient γH+ = 165.4 when using the MacInnes convention for scaling Pitzer single ion activity coefficient [8]. A superacid is an acid with an acidity greater than that of 100% sulfuric acid. ... In chemistry, a superbase is an extremely strong base. ... The Activity coefficient for chemicals in a mixture is an indicator of what the concentration of that chemical will be in a vapor of the mixture. ...


Arbitrarily, the pH is − log10([H + ]). Therefore,

pH = − log10[H + ]

or, by substitution,

mbox{pH} = frac{epsilon}{0.059}.

The "pH" of any other substance may also be found (e.g. the potential of silver ions, or pAg+) by deriving a similar equation using the same process. These other equations for potentials will not be the same, however, as the number of moles of electrons transferred (n) will differ for the different reactions.


Calculation of pH for weak and strong acids

Values of pH for weak and strong acids can be approximated using certain assumptions.


Under the Brønsted-Lowry theory, stronger or weaker acids are a relative concept. But here we define a strong acid as a species which is a much stronger acid than the hydronium (H3O+) ion. In that case the dissociation reaction (strictly HX+H2O↔H3O++X but simplified as HX↔H++X) goes to completion, i.e. no unreacted acid remains in solution. Dissolving the strong acid HCl in water can therefore be expressed: Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Mineral acids Organic acids Bases: Strong bases Weak bases Organic bases edit An acid-base reaction is a chemical reaction between an acid and a... R-phrases , S-phrases , , Flash point Non-flammable. ...

HCl(aq) → H+ + Cl

This means that in a 0.01 mol/L solution of HCl it is approximated that there is a concentration of 0.01 mol/L dissolved hydrogen ions. From above, the pH is: pH = −log10 [H+]:

pH = −log (0.01)

which equals 2.


For weak acids, the dissociation reaction does not go to completion. An equilibrium is reached between the hydrogen ions and the conjugate base. The following shows the equilibrium reaction between methanoic acid and its ions: Apparatus for carrying out acid-base titration. ... Within the Brønsted-Lowry (protonic) theory of acids and bases, a conjugate acid is the acid member, HX, of a pair of two compounds that transform into each other by gain or loss of a proton. ... Formic acid (systematically called methanoic acid) is the simplest carboxylic acid. ...

HCOOH(aq) ↔ H+ + HCOO

It is necessary to know the value of the equilibrium constant of the reaction for each acid in order to calculate its pH. In the context of pH, this is termed the acidity constant of the acid but is worked out in the same way (see chemical equilibrium): In chemistry, the equilibrium constant is a quantity characterizing a chemical equilibrium in a chemical reaction. ... ... Apparatus for carrying out acid-base titration. ...

Ka = [hydrogen ions][acid ions] / [acid]

For HCOOH, Ka = 1.6 × 10−4


When calculating the pH of a weak acid, it is usually assumed that the water does not provide any hydrogen ions. This simplifies the calculation, and the concentration provided by water, 1×10−7 mol/L, is usually insignificant.


With a 0.1 mol/L solution of methanoic acid (HCOOH), the acidity constant is equal to:

Ka = [H+][HCOO] / [HCOOH]

Given that an unknown amount of the acid has dissociated, [HCOOH] will be reduced by this amount, while [H+] and [HCOO] will each be increased by this amount. Therefore, [HCOOH] may be replaced by 0.1 − x, and [H+] and [HCOO] may each be replaced by x, giving us the following equation:

1.6times 10^{-4} = frac{x^2}{0.1-x}.

Solving this for x yields 3.9×10−3, which is the concentration of hydrogen ions after dissociation. Therefore the pH is −log(3.9×10−3), or about 2.4.


Measurement

Representative pH values
Substance pH
Hydrochloric acid, 10M
-1.0
Lead-acid battery
0.5
Gastric acid
1.5 – 2.0
Lemon juice
2.4
Cola
2.5
Vinegar
2.9
Orange or apple juice
3.5
Tomato Juice
4.0
Beer
4.5
Acid Rain
<5.0
Coffee
5.0
Tea or healthy skin
5.5
Urine
6.0
Milk
6.5
Pure Water
7.0
Healthy human saliva
6.5 – 7.4
Blood
7.34 – 7.45
Seawater
7.7 – 8.3
Hand soap
9.0 – 10.0
Household ammonia
11.5
Bleach
12.5
Household lye
13.5

pH can be measured:
R-phrases , S-phrases , , Flash point Non-flammable. ... A valve-regulated, sometimes called sealed, lead acid battery Lead-acid batteries, invented in 1859 by French physicist Gaston Planté, are the oldest type of rechargeable battery. ... Gastric acid is, together with several enzymes and the intrinsic factor, one of the main secretions of the stomach. ... This article is about the fruit. ... For other uses, see Cola (disambiguation). ... Vinegar is sometimes infused with spices or herbs—as here, with oregano. ... Binomial name (L.) Osbeck Orange—specifically, sweet orange—refers to the citrus tree Citrus sinensis (syn. ... This article is about the fruit. ... Tomato juice is a juice made from squeezed tomatoes. ... For other uses, see Beer (disambiguation). ... The term acid rain is commonly used to mean the deposition of acidic components in rain, snow, fog, dew, or dry particles. ... For other uses, see Coffee (disambiguation). ... For other uses, see Tea (disambiguation). ... For other uses, see Skin (disambiguation). ... This article is about the urine of animals generally. ... A glass of cows milk. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article is about modern humans. ... Saliva is the watery and usually frothy substance produced in the mouths of humans and some animals. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... Annual mean sea surface salinity for the World Ocean. ... A collection of decorative soaps used for human hygiene purposes. ... For other uses, see Ammonia (disambiguation). ... This article is about the chemical whitener. ... Flash point Non-flammable. ...

  • by addition of a pH indicator into the solution under study. The indicator color varies depending on the pH of the solution. Using indicators, qualitative determinations can be made with universal indicators that have broad color variability over a wide pH range and quantitative determinations can be made using indicators that have strong color variability over a small pH range. Precise measurements can be made over a wide pH range using indicators that have multiple equilibriums in conjunction with spectrophotometric methods to determine the relative abundance of each pH-dependent component that make up the color of solution [citation needed], or
  • by using a pH meter together with pH-selective electrodes (pH glass electrode, hydrogen electrode, quinhydrone electrode, ion sensitive field effect transistor and others).
  • by using pH paper, indicator paper that turns color corresponding to a pH on a color key. pH paper is usually small strips of paper (or a continuous tape that can be torn) that has been soaked in an indicator solution, and is used for approximations.

The lowest and highest ends of the pH scale do not oxidize. The middle of the scale is what oxidizes, such as water and blood. Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit A... Spectrophotometer In physics, spectrophotometry is the quantitative study of electromagnetic spectra. ... A pH meter is an electronic instrument used to measure the pH (acidity or basicity) of a liquid (though special probes are sometimes used to measure the pH of semi-solid substances, such as cheese). ... Glass electrode is a potentiometric sensor made from glass of f specific composition. ... A standard hydrogen electrode (abbreviated SHE) is a redox electrode which is placed in the basis of the thermodynamic scale of oxidation-reduction potentials. ... quinhydrone electrode One of several oxidation-reduction electrodes in which the ratio of the two forms (quinone-quinhydrone), determined by the hydrogen ion concentration, sets up a potential that can be measured and converted to a pH value (fails above pH 8). ... An ISFET is an Ion Sensitive Field Effect Transistor; When the ion concentration (or pH) changes, less current will flow through the transistor. ...


As the pH scale is logarithmic, it does not start at zero. Thus the most acidic of liquids encountered can have a pH as low as −5. The most alkaline typically has pH of 14. Measurement of extremely low pH values has various complications. Calibration of the electrode in such cases can be done with standard solutions of concentrated sulphuric acid whose pH values can be calculated with the Pitzer model[8].


As an example of home application, the measurement of pH value can be used to quantify the amount of acid in a swimming pool.


pOH

There is also pOH, in a sense the opposite of pH, which measures the concentration of OH ions, or the basicity. Since water self ionizes, and notating [OH] as the concentration of hydroxide ions, we have Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit In... Hydroxide is a polyatomic ion consisting of oxygen and hydrogen: OH− It has a charge of −1. ...

 K_w = a_{{rm{H}}^ * } a_{{rm{OH}}^ - }= 10^{ - 14} (*)

where Kw is the ionization constant of water.


Now, since

log _{10} K_w = log _{10} a_{{rm{H}}^ + } + log _{10} a_{{rm{OH}}^ - }

by logarithmic identities, we then have the relationship: In mathematics, there are several logarithmic identities. ...

- 14 = {rm{log}}_{{rm{10}}} ,a_{{rm{H}}^{rm{ + }} } + log _{10} ,a_{{rm{OH}}^ - }

and thus

{rm{pOH}} = - log _{10} ,a_{{rm{OH}}^ - } = 14 + log _{10} ,a_{{rm{H}}^ + } = 14 - {rm{pH}}

This formula is valid exactly for temperature = 298.15 K (25 °C) only, but is acceptable for most lab calculations.


Indicators

The Hydrangea macrophylla blossoms in pink or blue, depending on soil pH. In acidic soils, the flowers are blue; in alkaline soils, the flowers are pink.
The Hydrangea macrophylla blossoms in pink or blue, depending on soil pH. In acidic soils, the flowers are blue; in alkaline soils, the flowers are pink.

An indicator is used to measure the pH of a substance. Common indicators are litmus paper, phenolphthalein, methyl orange, phenol red, bromothymol blue, bromocresol green and bromocresol purple. To demonstrate the principle with common household materials, red cabbage, which contains the dye anthocyanin, is used.[9] Download high resolution version (2016x1512, 1070 KB) File links The following pages link to this file: PH Hydrangea Wikipedia:Recent additions User:Raul654/favpics/Longwood Hydrangea macrophylla ... Download high resolution version (2016x1512, 1070 KB) File links The following pages link to this file: PH Hydrangea Wikipedia:Recent additions User:Raul654/favpics/Longwood Hydrangea macrophylla ... Binomial name Hydrangea macrophylla (Thunb. ... This article is about the color. ... For other uses, see Blue (disambiguation). ... Acids and bases: Acid-base extraction Acid-base reaction Acid dissociation constant Acidity function Buffer solutions pH Proton affinity Self-ionization of water Acids: Lewis acids Mineral acids Organic acids Strong acids Superacids Weak acids Bases: Lewis bases Organic bases Strong bases Superbases Non-nucleophilic bases Weak bases edit A... The term litmus test can be literal or metaphorical. ... Phenolphthalein is a sensitive chemical with the formula C20H14O4 (often written as HIn in shorthand notation). ... Methyl Orange is a pH indicator frequently used in titrations. ... Phenol red (also known as phenolsulfonphthalein or PSP) is a pH indicator that is frequently used in cell biology laboratories and home swimming pool test kits. ... Bromothymol Blue (also known as dibromothymolsulfonephthalein, Bromthymol Blue, and BTB) is a chemical indicator for weak acids and bases. ... Bromocresol green (3,3,5,5-tetrabromo-m-cresolsulfonphthalein) is a dye of the triphenylmethane family (triarylmethane dyes), which is used as a pH indicator and as a tracking dye for DNA agarose gel electrophoresis. ... Bromocresol purple,or 5,5-dibromo-o-cresolsulfophthalein, is a pH indicator with the chemical formula C21H16Br2O5S. // Chemical properties The compound, with a molecular weight of 540. ... Cultivar Group Brassica oleracea Capitata Group The Red Cabbage (Brassica oleracea var. ... Plants with abnormally high anthocyanin quantities are popular as ornamental plants - here, a selected purple-leaf cultivar of European Beech Anthocyanins (from Greek: (anthos) = flower + (kyanos) = blue) are water-soluble vacuolar flavonoid pigments that appear red to blue, according to pH. They are synthesized exclusively by organisms of the plant...


Seawater

In chemical oceanography pH measurement is complicated by the chemical properties of seawater, and several distinct pH scales exist[10]. Chemical oceanography is the study of the behaviour of the chemical elements within the Earths oceans. ... The phrase chemical property is context-dependent, but generally refers to a materials behavior at ambient conditions (i. ... Annual mean sea surface salinity for the World Ocean. ...


As part of its operational definition of the pH scale, the IUPAC define a series of buffer solutions across a range of pH values (often denoted with NBS or NIST designation). These solutions have a relatively low ionic strength (~0.1) compared to that of seawater (~0.7), and consequently are not recommended for use in characterising the pH of seawater (since the ionic strength differences cause changes in electrode potential). To resolve this problem, an alternative series of buffers based on artificial seawater was developed[11]. This new series resolves the problem of ionic strength differences between samples and the buffers, and the new pH scale is referred to as the total scale, often denoted as pHT. An operational definition of a quantity is the description of a specific process, or set of validation tests, accessible to more persons than the definer (i. ... The International Union of Pure and Applied Chemistry (IUPAC) is an international non-governmental organization devoted to the advancement of chemistry. ... Acids and bases: Acid-base reaction theories pH Self-ionization of water Buffer solutions Systematic naming Electrochemistry Acid-base extraction Acids: Strong acids Weak acids Superacids Lewis acids Mineral acids Organic acids Bases: Strong bases Weak bases Superbases Lewis bases Organic bases edit Buffer solutions are solutions which resist change... As a non-regulatory agency of the United States Department of Commerce&#8217;s Technology Administration, the National Institute of Standards (NIST) develops and promotes measurement, standards, and technology to enhance productivity, facilitate trade, and improve the quality of life. ... NIST logo The National Institute of Standards and Technology (NIST, formerly known as The National Bureau of Standards) is a non-regulatory agency of the United States Department of Commerce’s Technology Administration. ... The ionic strength of a solution is a function of the concentration of all ions present in a solution. ... It has been suggested that Electrode potential be merged into this article or section. ... Artificial seawater (or ASW) is a mixture of dissolved mineral salts (and sometimes vitamins) that simulates seawater. ...


The total scale was defined using a medium containing sulphate ions. These ions experience protonation, H+ + SO42− HSO4, such that the total scale includes the effect of both protons ("free" hydrogen ions) and hydrogen sulphate ions: Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. ... Protonation is the addition of a proton (H+) to an atom, molecule, or ion. ... For other uses, see Proton (disambiguation). ...

[H+]T = [H+]F + [HSO4]

An alternative scale, the free scale, often denoted pHF, omits this consideration and focuses solely on [H+]F, in principle making it a simpler representation of hydrogen ion concentration. Analytically, only [H+]T can be determined[12], so [H+]F must be estimated using the [SO42−] and the stability constant of HSO4, KS*:

[H+]F = [H+]T − [HSO4] = [H+]T ( 1 + [SO42−] / KS* )−1

However, it is difficult to estimate KS* in seawater, limiting the utility of the otherwise more straightforward free scale.


Another scale, known as the seawater scale, often denoted pHSWS, takes account of a further protonation relationship between hydrogen ions and fluoride ions, H+ + F HF. Resulting in the following expression for [H+]SWS: Fluoride is the ionic form of fluorine. ...

[H+]SWS = [H+]F + [HSO4] + [HF]

However, the advantage of considering this additional complexity is dependent upon the abundance of fluoride in the medium. In seawater, for instance, sulphate ions occur at much greater concentrations (> 400 times) than those of fluoride. Consequently, for most practical purposes, the difference between the total and seawater scales is very small.


The following three equations summarise the three scales of pH:

pHF = − log [H+]F
pHT = − log ( [H+]F + [HSO4] ) = − log [H+]T
pHSWS = − log ( [H+]F + [HSO4] + [HF] ) = − log [H+]SWS

In practical terms, the three seawater pH scales differ in their values by up to 0.12 pH units[10], differences that are much larger than the accuracy of pH measurements typically required (particularly in relation to the ocean's carbonate system). Since it omits consideration of sulphate and fluoride ions, the free scale is significantly different from both the total and seawater scales. Because of the relative unimportance of the fluoride ion, the total and seawater scales differ only very slightly. The total inorganic carbon (CT, or TIC)is the sum of inorganic carbon species in a solution. ...


References

  1. ^ http://www.jp.horiba.com/story_e/ph/ph01_03.htm
  2. ^ http://chem.lapeer.org/Chem2Docs/pHFacts.html
  3. ^ Carlsberg Research Centre history page, http://www.crc.dk/history.shtml
  4. ^ http://www.madsci.org/posts/archives/sep2001/1000136604.Sh.r.html
  5. ^ http://www.morrisonlabs.com/ph_study_guide.htm
  6. ^ International Standard ISO 31-8: Quantities and units – Part 8: Physical chemistry and molecular physics, Annex C (normative): pH. International Organization for Standardization, 1992.
  7. ^ Definitions of pH scales, standard reference values, measurement of pH, and related terminology. Pure Appl. Chem. (1985), 57, pp 531–542.
  8. ^ a b c Nordstrom, DK et al (2000) Negative pH and extremely acidic mine waters from Iron Mountain California. Environ Sci Technol,34, 254-258.
  9. ^ chemistry.about.com
  10. ^ a b Zeebe, R. E. and Wolf-Gladrow, D. (2001) CO2 in seawater: equilibrium, kinetics, isotopes, Elsevier Science B.V., Amsterdam, Netherlands (ISBN 0 444 50946 1).
  11. ^ Hansson, I. (1973) A new set of pH-scales and standard buffers for seawater. Deep Sea Research, 20: 479-491.
  12. ^ Dickson, A. G. (1984) pH scales and proton-transfer reactions in saline media such as sea water. Geochim. Cosmochim. Acta, 48: 2299–2308.

ISO 31-8 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to physical chemistry and molecular physics. ... “ISO” redirects here. ...

See also

For acidosis referring to acidity of the urine, see renal tubular acidosis. ... Alkalosis refers to a condition reducing hydrogen ion concentration of arterial blood plasma. ...

External links


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