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In water, measurable pK a values range from about −2 for a strong acid to about 12 for a very weak acid (or strong base). A buffer solution of a desired pH can be prepared as a mixture of a weak acid and its conjugate base. In practice, the mixture can be created by dissolving the acid in water, and adding the requisite amount of strong acid ...
For example, acetic acid is a weak acid which has a = 1.75 x 10 −5. Its conjugate base is the acetate ion with K b = 10 −14 /K a = 5.7 x 10 −10 (from the relationship K a × K b = 10 −14), which certainly does not correspond to a strong base. The conjugate of a weak acid is often a weak base and vice versa.
Strong acids, such as sulfuric or phosphoric acid, have large dissociation constants; weak acids, such as acetic acid, have small dissociation constants. The symbol K a , used for the acid dissociation constant, can lead to confusion with the association constant , and it may be necessary to see the reaction or the equilibrium expression to ...
A weak acid may be defined as an acid with pK a greater than about −2. An acid with pK a = −2 would be 99 % dissociated at pH 0, that is, in a 1 M HCl solution. Any acid with a pK a less than about −2 is said to be a strong acid. Strong acids are said to be fully dissociated.
When the difference between successive pK a values is less than about 3, there is overlap between the pH range of existence of the species in equilibrium. The smaller the difference, the more the overlap. In the case of citric acid, the overlap is extensive and solutions of citric acid are buffered over the whole range of pH 2.5 to 7.5.
A variety of amines and nitrogen heterocycles are useful bases of moderate strength (pK a of conjugate acid around 10-13) . N,N-Diisopropylethylamine (DIPEA, also called Hünig's Base [1]), pK a = 10.75
K a is variously named a dissociation constant, [3] an acid ionization constant, [2]: 668 an acidity constant [1] or an ionization constant. [2]: 708 It serves as an indicator of the acid strength: stronger acids have a higher K a value (and a lower pK a value).
Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic. Since most naturally occurring organic compounds are weak electrolytes, such as carboxylic acids and amines, pH indicators find many applications in biology and analytical chemistry. Moreover, pH indicators form one of the three main types ...