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The pH scale is by far the most commonly used acidity function, and is ideal for dilute aqueous solutions. Other acidity functions have been proposed for different environments, most notably the Hammett acidity function , H 0 , [ 3 ] for superacid media and its modified version H − for superbasic media.
In such cases, the system can be treated as a mixture of the acid or base and water, which is an amphoteric substance. By accounting for the self-ionization of water, the true pH of the solution can be calculated. For example, a 5×10 −8 M solution of HCl would have a pH of 6.89 when treated as a mixture of HCl and water. The self-ionization ...
Water is amphoteric: it has the ability to act as either an acid or a base in chemical reactions. [87] According to the Brønsted-Lowry definition, an acid is a proton (H +) donor and a base is a proton acceptor. [88] When reacting with a stronger acid, water acts as a base; when reacting with a stronger base, it acts as an acid. [88]
Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H +, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH −) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7 in an ideal state. Acids ...
3] have become converted to carbonic acid [H 2 CO 3] at this pH. This pH is also called the CO 2 equivalence point where the major component in water is dissolved CO 2 which is converted to H 2 CO 3 in an aqueous solution. There are no strong acids or bases at this point.
A basic salt of an alkali metal or alkaline earth metal [2] (this includes Mg(OH) 2 (magnesium hydroxide) but excludes NH 3 ). Any base that is soluble in water and forms hydroxide ions [3] [4] or the solution of a base in water. [5] (This includes both Mg(OH) 2 and NH 3, which forms NH 4 OH.) The second subset of bases is also called an ...
With pOH obtained from the pOH formula given above, the pH of the base can then be calculated from =, where pK w = 14.00. A weak base persists in chemical equilibrium in much the same way as a weak acid does, with a base dissociation constant (K b) indicating the strength of the base. For example, when ammonia is put in water, the following ...
A hot water solution containing 73.1% (mass) of NaOH is a eutectic that solidifies at about 62.63 °C as an intimate mix of anhydrous and monohydrate crystals. [21] [20] A second stable eutectic composition is 45.4% (mass) of NaOH, that solidifies at about 4.9 °C into a mixture of crystals of the dihydrate and of the 3.5-hydrate. [13]