pH is the measure of the acidity or basicity of a solution. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Acid-base extraction is a procedure using sequential Liquid-liquid extractions to purify Acids and bases from mixtures based on their chemical properties Acid-base homeostasis is the part of Human homeostasis concerning the proper balance between Acids and bases, in other words the PH. An acidity function is a measure of the Acidity of a medium or solvent system usually expressed in terms of its ability to donate protons to (or accept protons from a For an individual weak acid or weak base component see Buffering agent. The proton affinity, E pa of a Anion or of a neutral Atom or Molecule is a measure of its gas-phase basicity. The self-ionization of water (also autoionization of water, and autodissociation of water) is the chemical reaction in which two water molecules react to produce a In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are A mineral acid is an Acid derived by Chemical reaction from inorganic Minerals as opposed to Organic acids These have Hydrogen An organic acid is an Organic compound with Acidic properties A Strong acid is an Acid that Ionizes completely in an Aqueous solution (not in the case of Sulfuric acid as it is diprotic A superacid is an Acid with an Acidity greater than that of 100% Sulfuric acid, which has a Hammett acidity function ( H 0 A weak acid is an Acid that does not completely donate all of its hydrogens when dissolved in water In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and An organic base is an Organic compound which acts as a base. Organic bases are usually but not always proton acceptors In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and In Chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase but most chemists would accept As the name suggests a non-nucleophilic base is an organic base that is a very Strong base but at the same time a poor Nucleophile. In chemistry a weak base is a Chemical base that does not Ionize fully in an Aqueous solution. In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances It is formally a measure of the activity of dissolved hydrogen ions (H⁺), but for very dilute solutions, the molarity (molar concentration) of H⁺ may be used as a substitute with little loss of accuracy. Activity in Chemistry is a measure of an “effective concentration” of a species Hydrogen ion is recommended by IUPAC as a general term for all Ions of Hydrogen and its Isotopes Depending on the Charge of the ion In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance In Chemistry, molar concentration, also called molarity, is a measure of the Concentration of a Solute in a Solution, or of any ^[1] In solution, hydrogen ions occur as a number of cations including hydronium ions (H₃O⁺). An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge In Chemistry, hydronium is the obsolete name for the Cation H 3 O + derived from Protonation of Water ^[2]

In pure water at 25 °C, the concentration of H⁺ equals the concentration of hydroxide ions (OH^-). The Celsius Temperature scale was previously known as the centigrade scale. In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen This is defined as "neutral" and corresponds to a pH level of 7. 0. Solutions in which the concentration of H⁺ exceeds that of OH^- have a pH value lower than 7. 0 and are known as acids. Solutions in which OH^- exceeds H⁺ have a pH value greater than 7. 0 known as bases. 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.

The concept of pH was first introduced by Danish chemist S. P. L. Sørensen at the Carlsberg Laboratory in 1909. The term Dane may refer to People with a Danish ancestral or ethnic identity whether living in Denmark, emigrants or the descendants of emigrants A chemist is a Scientist trained in the Science of Chemistry. Søren Peder Lauritz Sørensen ( January 9, 1868 - February 12, 1939) was a Danish Chemist, famous for the introduction The Carlsberg Laboratory in Copenhagen, Denmark was created in 1875 by J Year 1909 ( MCMIX) was a Common year starting on Friday (link will display full calendar of the Gregorian calendar (or a Common year starting ^[3] The name pH has been claimed to have come from any of several sources including: pondus hydrogenii, potentia hydrogenii (Latin),^[4] potentiel hydrogène (French), and potential of hydrogen (English). Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. French ( français,) is a Romance language spoken around the world by 118 million people as a native language and by about 180 to 260 million people English is a West Germanic language originating in England and is the First language for most people in the United Kingdom, the United States ^[5]

Contents 1 Definition 2 Explanation 3 Calculation of pH for weak and strong acids 4 Measurement 5 pOH 6 Indicators 7 Seawater 8 Body fluids 9 See also 10 References 11 External links

Definition

The operational definition of pH is officially defined by International Standard ISO 31-8 as follows: ^[6] For a solution X, first measure the electromotive force E_X of the galvanic cell

reference electrode | concentrated solution of KCl || solution X | H₂ | Pt

and then also measure the electromotive force E_S of a galvanic cell that differs from the above one only by the replacement of the solution X of unknown pH, pH(X), by a solution S of a known standard pH, pH(S). An operational definition is a demonstration of a process &mdash such as a Variable, term, or object &mdash relative in terms of the specific Process ISO 31-8 is the part of International standard ISO 31 that defines names and symbols for quantities and units related to Physical chemistry Electromotive force ( emf, \mathcal{E} is a term used to characterize electrical devices such as Voltaic cells thermoelectric devices electrical 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 The pH of X is then

where

F is the Faraday constant;

R is the molar gas constant;

T is the thermodynamic temperature. In Physics and Chemistry, the Faraday constant (named after Michael Faraday) is the magnitude of Electric charge per mole of Relationship with the Boltzmann constant The Boltzmann constant kB (often abbreviated k) may be used in place of the gas constant by working Thermodynamic temperature is the absolute measure of Temperature and is one of the principal parameters of Thermodynamics.

Defined this way, pH is a dimensionless quantity. In Dimensional analysis, a dimensionless quantity (or more precisely a quantity with the dimensions of 1) is a Quantity without any Physical units Values pH(S) for a range of standard solutions S, along with further details, are given in the relevant IUPAC recommendation. The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization ^[7]

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

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. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are An activity coefficient is a factor used in Thermodynamics to account for deviations from ideal behaviour in a Mixture of Chemical substances In an In Chemistry, valence, also known as valency or valency number, is a measure of the number of Chemical bonds formed by the Atoms An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium

Simplified definition

pH is a measurement of the concentration of hydrogen ions in a solution. Because of its mathematical formulation, low pH values are associated with solutions with high concentrations of hydrogen ions, while high pH values occur for solutions with low concentrations of hydrogen ions. Pure water has a pH of 7. 0, and other solutions are usually described with reference to this value. Acids are defined as those solutions that have a pH less than 7 (i. e. more hydrogen ions than water); while bases are defined as those solutions that have a pH greater than 7 (i. e. less hydrogen ions than water).

The definitions of weak- and strong acids, and weak- and strong bases does not refer to pH, but instead describes whether an acid or base ionizes in solution. A weak acid is an Acid that does not completely donate all of its hydrogens when dissolved in water A Strong acid is an Acid that Ionizes completely in an Aqueous solution (not in the case of Sulfuric acid as it is diprotic In chemistry a weak base is a Chemical base that does not Ionize fully in an Aqueous solution. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons

Explanation

In simpler terms, the number arises from a measure of the activity of hydrogen ions or their equivalent in the solution. Activity in Chemistry is a measure of an “effective concentration” of a species Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 The pH scale is an inverse logarithmic representation of hydrogen proton (H⁺) concentration. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce Hydrogen ion is recommended by IUPAC as a general term for all Ions of Hydrogen and its Isotopes Depending on the Charge of the ion Unlike linear scales, which have a constant relationship 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:

Where α_H⁺ denotes the activity of H⁺ ions, and is dimensionless. In Dimensional analysis, a dimensionless quantity (or more precisely a quantity with the dimensions of 1) is a Quantity without any Physical units 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 dilute solutions such as tap water, activity is approximately equal to the numeric value of the concentration of the H⁺ ion, denoted as [H⁺] ([H₃O⁺]), measured in moles per litre (also known as molarity). Tap water ( running water) is part of indoor Plumbing, which became available in the late 19th century and common in the mid-20th century In Chemistry, hydronium is the obsolete name for the Cation H 3 O + derived from Protonation of Water The mole (symbol mol) is a unit of Amount of substance: it is an SI base unit, and almost the only unit to be used to measure this The litre or liter (see spelling differences) is a unit of Volume. In Chemistry, concentration is the measure of how much of a given substance there is mixed with another substance Therefore, it is often convenient to define pH as:

For both definitions, log₁₀ denotes the base-10 logarithm, therefore pH defines a logarithmic scale of acidity. In Mathematics, the logarithm of a number to a given base is the power or Exponent to which the base must be raised in order to produce Definition and base Logarithmic scales are either defined for ratios of the underlying quantity or one has to agree to measure For example, if one makes a lemonade with a H⁺ concentration of 0. Lemonade is a Lemon -flavored Soft drink. The term can refer to two different types of beverage In the U 0050 moles per litre, its pH would be:

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 α_H⁺ 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. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 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. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3 7.

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 significant figures (also called significant digits and abbreviated sig figs) of a number are those digits that carry meaning contributing to its accuracy 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 when its pH at 50 °C is around 6. 55, and also that a pH of 7. 00 is very slightly basic.

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. A superacid is an Acid with an Acidity greater than that of 100% Sulfuric acid, which has a Hammett acidity function ( H 0 In Chemistry, a superbase is an extremely strong base. There is no commonly accepted definition for what qualifies as a superbase but most chemists would accept 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 α_H⁺ around 1350 and activity coefficient γ_H⁺ = 165. An activity coefficient is a factor used in Thermodynamics to account for deviations from ideal behaviour in a Mixture of Chemical substances In an 4 when using the MacInnes convention for scaling Pitzer single ion activity coefficient. ^[8]

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

pH = − log₁₀[H ⁺ ]

or, by substitution,

.

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 weak and strong acids can be approximated using certain theories and 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:

HCl(aq) → H⁺ + Cl⁻

This means that in a 0. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water 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. In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change 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 The following shows the equilibrium reaction between methanoic acid and its ions:

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. Formic acid (systematically called methanoic acid) is the simplest Carboxylic acid. For a general Chemical reaction \alpha A +\beta B. \rightleftharpoons \sigma S+\tau T. 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):

K_a = [hydrogen ions][acid ions] / [acid]

For HCOOH, K_a = 1. In a Chemical process, chemical equilibrium is the state in which the chemical activities or Concentrations of the reactants and products have no net change 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:

K_a = [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:

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. Hydrochloric acid is the Solution of Hydrogen chloride ( H[[Chlorine Cl]] in water 0
Lead-acid battery	0. Lead-acid batteries, invented in 1859 by French Physicist Gaston Planté, are the oldest type of Rechargeable battery. 5
Gastric acid	1. Gastric acid is one of the main Secretions of the Stomach, together with several Enzymes and Intrinsic factor. 5 – 2. 0
Lemon juice	2. The lemon ( Citrus × limon) is a hybrid in cultivated wild plants 4
Cola	2. Cola is a sweet carbonated drink usually with Caramel coloring and containing Caffeine. 5
Vinegar	2. Vinegar is an acidic liquid processed from the Fermentation of Ethanol in a process that yields its key ingredient Acetic acid (also called ethanoic acid 9
Orange or apple juice	3. An orange —specifically the sweet orange —is the Citrus fruit Citrus sinensis ( syn The apple is the pomaceous Fruit of the apple tree Species Malus domestica in the Rose family Rosaceae. 5
Tomato Juice	4. Tomato juice is a Juice made from squeezed Tomatoes It is usually used as a Beverage, either plain or in Cocktails such as a Bloody Mary 0
Beer	4. Beer is the world's oldest and most widely consumed Alcoholic beverage and the third most popular drink overall after water and tea 5
Acid Rain	<5. Acid rain is Rain or any other form of precipitation that is unusually Acidic It has harmful effects on plants aquatic animals and infastructure 0
Coffee	5. CoFFEE is an Open source Software for computer supported collaborative learning (CSCL in a digital classroom 0
Tea or healthy skin	5. Tea refers to the cured agricultural product of the leaves leaf buds and internodes of Camellia sinensis, which have been prepared and cured for the market The skin is the outer covering of living tissue of an animal (or plant 0
Urine	6. Urine is a liquid waste product of the body secreted by the Kidneys by a process of filtration from Blood and Excreted through the Urethra. 0
Milk	6. Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. 5
Pure Water	7. Water is a common Chemical substance that is essential for the survival of all known forms of Life. 0
Healthy human saliva	6. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus For the band see Saliva (band; for the village in Azerbaijan see Səliva. 5 – 7. 4
Blood	7. Blood is a specialized Bodily fluid that delivers necessary substances to the body's cells ��such as nutrients and oxygen—and transports Waste products 34 – 7. 45
Seawater	7. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3 7 – 8. 3
Hand soap	9. SOAP (see below for name and origins is a protocol for exchanging XML -based messages over Computer networks normally using 0 – 10. 0
Household ammonia	11. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor 5
Bleach	12. A bleach is a Chemical that removes color or whitens often via Oxidation. 5
Household lye	13. Sodium hydroxide ( Na[[hydroxide OH]]) also known as Lye, caustic soda and (incorrectly according to IUPAC nomenclature 5

pH can be measured:

• by addition of a pH indicator into the solution under study. A pH indicator is a halochromic chemical compound that is added in small amounts to a Solution so that the PH ( Acidity or 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 , 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). In Physics, spectrophotometry is the quantitative study of electromagnetic spectra. A pH meter is an electronic instrument used to measure the PH ( Acidity or alkalinity) of a liquid (though special probes are sometimes used to measure A glass electrode is a type of Ion-selective electrode made of a doped glass membrane that is sensitive to a specific ion The standard hydrogen electrode (abbreviated SHE) also called normal hydrogen electrode ( NHE) is a Redox electrode which forms the basis of Quinhydrone electrode is one of several oxidation-reduction Electrode 's used for measuring hydrogen ion concentration or PH. An ISFET is an ion-sensitive Field effect transistor used to measure ion concentrations in solution when the ion concentration (such as PH) changes the current through
• by using pH paper, indicator paper that turns color corresponding to a pH on a color key. pH paper is usually strips of paper that has been soaked in an indicator solution, and is used for approximations.

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 sulfuric 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 alkalinity. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Since water self ionizes, and notating [OH⁻] as the concentration of hydroxide ions, we have

(*)

where K_w is the ionization constant of water. In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen

Now, since

by logarithmic identities, we then have the relationship:

and thus

Also, this formula is valid exactly for temperature = 298. In Mathematics, there are several logarithmic identities. Algebraic identities Using simpler operations Logarithms can be used 15 K (25 °C) only, but is acceptable for most lab calculations.

Indicators

An indicator is used to measure the pH of a substance. A pH indicator is a halochromic chemical compound that is added in small amounts to a Solution so that the PH ( Acidity or Common indicators are litmus paper, phenolphthalein, methyl orange, phenol red, bromothymol blue, bromocresol green and bromocresol purple. Litmus is a Water - Soluble mixture of different Dyes Extracted from Lichens, especially Roccella tinctoria. Phenolphthalein is a Chemical compound with the formula C 20 H 14 O 4 (often written as " HIn 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 Bromothymol Blue (also known as dibromothymolsulfonephthalein, Bromthymol Blue, and BTB) is a chemical indicator for weak acids and Bromocresol Green (BCG is a dye of the Triphenylmethane family ( Triarylmethane dyes, which is used as a PH indicator and as a Tracking dye Bromocresol Purple (BCP,or 5'5"-dibromo-o-cresolsulfophthalein is a PH indicator with the Chemical formula C21H16Br2O5S To demonstrate the principle with common household materials, red cabbage, which contains the dye anthocyanin, is used. The Red Cabbage ( Brassica oleracea var capitata f rubra) is a sort of Cabbage, also known as Red Kraut or Blue Kraut Not to be confused with Anthocyanidin, their sugar free counterparts ^[9]

In addition to red cabbage, some flower petals (like hibiscus, marigold) when crushed onto a white paper, the bluish stain that is imparted on the paper may be used as a 'homemade litmus'. The Red Cabbage ( Brassica oleracea var capitata f rubra) is a sort of Cabbage, also known as Red Kraut or Blue Kraut Hibiscus, or rosemallow, is a large genus of about 200&ndash220 species of Flowering plants in the family Malvaceae (the mallow family Addition of acidic substances will make it red; and when alkaline substances are added to this red litmus, it turns blue.

Seawater

In chemical oceanography pH measurement is complicated by the chemical properties of seawater, and several distinct pH scales exist. Chemical oceanography is the study of the behavior of the Chemical elements within the Earth 's Oceans The ocean is unique in that it contains - in greater A chemical property is any of a material's properties that becomes evident during a Chemical reaction; that is any quality that can be established only by changing a substance's Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3 ^[10]

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). An operational definition is a demonstration of a process &mdash such as a Variable, term, or object &mdash relative in terms of the specific Process The International Union of Pure and Applied Chemistry ( IUPAC) (aɪjuːpæk or ay-yoo-pec) is an international Non-governmental organization For an individual weak acid or weak base component see Buffering agent. These solutions have a relatively low ionic strength (~0. The ionic strength, I, of a solution is a function of the Concentration of all Ions present in a Solution. 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. In Electrochemistry, the standard electrode potential, abbreviated Eo E0 or EO (with a superscript Plimsoll character pronounced To resolve this problem, an alternative series of buffers based on artificial seawater was developed. Artificial seawater (or ASW) is a mixture of dissolved mineral salts (and sometimes Vitamins that simulates Seawater. ^[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 pH_T.

The total scale was defined using a medium containing sulfate ions. These ions experience protonation, H⁺ + SO₄²⁻ ⇌ HSO₄⁻, such that the total scale includes the effect of both protons (free hydrogen ions) and hydrogen sulfate ions:

[H⁺]_T = [H⁺]_F + [HSO₄⁻]

An alternative scale, the free scale, often denoted pH_F, omits this consideration and focuses solely on [H⁺]_F, in principle making it a simpler representation of hydrogen ion concentration. In chemistry protonation is the addition of a proton ( H[[Cation +]] to an Atom, Molecule, or Ion. The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive Analytically, only [H⁺]_T can be determined,^[12] therefore, [H⁺]_F must be estimated using the [SO₄²⁻] and the stability constant of HSO₄⁻, K_S^*:

[H⁺]_F = [H⁺]_T − [HSO₄⁻] = [H⁺]_T ( 1 + [SO₄²⁻] / K_S^* )⁻¹

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

Another scale, known as the seawater scale, often denoted pH_SWS, takes account of a further protonation relationship between hydrogen ions and fluoride ions, H⁺ + F⁻ ⇌ HF. Fluoride is the reduced form of Fluorine. Both organic and Inorganic compounds containing the element fluorine are considered fluorides Resulting in the following expression for [H⁺]_SWS:

[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, sulfate 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:

pH_F = − log [H⁺]_F

pH_T = − log ( [H⁺]_F + [HSO₄⁻] ) = − log [H⁺]_T

pH_SWS = − 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, differences that are much larger than the accuracy of pH measurements typically required, particularly in relation to the ocean's carbonate system. The total inorganic carbon (CT or TIC or dissolved inorganic carbon (DIC is the Sum of Inorganic Carbon species in a Solution ^[10] Since it omits consideration of sulfate 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.

Body fluids

pH in body fluids ^[13]

Fluid	pH
gastric acid	0. Gastric acid is one of the main Secretions of the Stomach, together with several Enzymes and Intrinsic factor. 7
lysosome	5. Lysosomes are Organelles that contain Digestive enzymes (acid Hydrolases. 5
granule of chromaffin cell	5. Chromaffin cells are Neuroendocrine cells found in the medulla of the Adrenal gland (suprarenal gland - located above the kidneys and in other ganglia 5
Neutral H2O at 37°C	6. 81
cytosol	7. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. 2
CSF	7. Cerebrospinal fluid ( CSF) Liquor cerebrospinalis, is a clear Bodily fluid that occupies the Subarachnoid space and the Ventricular system 3
arterial blood plasma	7. Arteries are Blood vessels that carry blood away from the Heart. Blood plasma is the Liquid component of Blood, in which the Blood cells are suspended 4
mitochondrial matrix	7. In the Mitochondrion, the matrix contains soluble Enzymes that catalyze the Oxidation of pyruvate and other small organic molecules 5
exocrine secretions of pancreas	8. The pancreas is a Gland organ in the digestive and Endocrine system of Vertebrates. 1

The pH of different body fluids varies with function and other factors. Bodily fluids listed below are found in the bodies of men and/or women Mostly it is a tightly regulated system to keep the acid-base homeostasis. Acid-base homeostasis is the part of Human homeostasis concerning the proper balance between Acids and bases, in other words the PH. These fluids may include urine, saliva, blood, and such. Another acid in the body is plaque. Plaque's pH is low and will dissolve teeth if not removed. The pH of blood is known to be slightly basic, at a value of 7. 4. pH is vital in maintaning the functioning of cells. For example, enzymes are heavily affected by changes in pH, and have an optimum pH at which they operate, otherwise they will denature and cease to catalyse vital reactions.

See also

• Acidosis
• Alkalosis
• S. P. L. Sørensen

References

External links

• Some Ka values
• Definition of pH IUPAC Gold Book
• The Measurement of pH - Definition, Standards and Procedures – Report of the Working Party on pH, IUPAC Provisional Recommendation (a proposal to revise the current IUPAC 1985 and ISO 31-8 definition of pH described above)

Compendium of Chemical Terminology (ISBN 0-86542-684-8 is a book published by IUPAC containing internationally accepted definitions for terms in Chemistry.

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