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In chemistry, pH () is a numeric scale used to specify the acidity or basicity of an aqueous solution. It is roughly the negative of the logarithm to base 10 of the concentration, measured in units of moles per liter, of hydrogen ions or H+. More precisely it is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are basic. Pure water is neutral, being neither an acid nor a base. Contrary to popular belief, the pH value can be less than 0 or greater than 14 for very strong acids and bases respectively. pH measurements are important in medicine, biology, chemistry, agriculture, forestry, food science, environmental science, oceanography, civil engineering, chemical engineering, nutrition, water treatment & water purification, and many other applications. The pH scale is traceable to a set of standard solutions whose pH is established by international agreement.〔 Primary pH standard values are determined using a concentration cell with transference, by measuring the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode. The pH of aqueous solutions can be measured with a glass electrode and a pH meter, or indicator. pH is the negative of the logarithm to base 10 of the activity of the (solvated) hydronium ion, more often (albeit somewhat inaccurately) expressed as the measure of the hydronium ion concentration.〔Bates, Roger G. ''Determination of pH: theory and practice''. Wiley, 1973.〕 ==History== The concept of p() was first introduced by Danish chemist Søren Peder Lauritz Sørensen at the Carlsberg Laboratory in 1909〔 Two other publications appeared in 1909 one in French and one in Danisch〕 and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", as so: pH. The exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation pH stands for "power of hydrogen".〔(【引用サイトリンク】title=Carlsberg Group Company History Page )〕 It has also been suggested that the "p" stands for the German ''Potenz'' (meaning "power"), others refer to French ''puissance'' (also meaning "power", based on the fact that the Carlsberg Laboratory was French-speaking). Another suggestion is that the "p" stands for the Latin terms ''pondus hydrogenii'' (engl. quantity of hydrogen), ''potentia hydrogenii'' (engl. capacity of hydrogen), or potential hydrogen. It is also suggested that Sørensen used the letters "p" and "q" (commonly paired letters in mathematics) simply to label the test solution (p) and the reference solution (q). Current use in chemistry is that p stands for "decimal cologarithm of", as also in the term p''K''a, used for acid dissociation constants. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「PH」の詳細全文を読む スポンサード リンク
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