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Stepwise dissociation constants are each defined for the loss of a single proton. The constant for dissociation of the first proton may be denoted as K a1 and the constants for dissociation of successive protons as K a2, etc. Phosphoric acid, H 3 PO 4, is an example of a polyprotic acid as it can lose three protons.
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 ...
The equilibrium constant for the protonation of a base, B, + H + ⇌ + is an association constant, K b, which is simply related to the dissociation constant of the conjugate acid, BH +. = The value of is ca. 14 at 25 °C. This approximation can be used when the correct value is not known.
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).
To find x, the acid dissociation constant (that is, the equilibrium constant for acid-base dissociation) must be specified. = [+] [] [] Substitute the concentrations with the values found in the last row of the ICE table.
In the case of the sample curve, the acid dissociation constant K a = 10-pKa would be approximately 1.78×10 −5 from visual inspection (the actual K a2 is 1.7×10 −5) For polyprotic acids, calculating the acid dissociation constants is only marginally more difficult: the first acid dissociation constant can be calculated the same way as it ...
where [H +] is the equilibrium concentration of H +, K a is the acid dissociation constant, C a and C b are the analytical concentrations of the acid and its conjugate base, respectively, and Δ = [H +] − [OH −]. The equation can be solved for [H +] by using the autoionization constant for water, K w, to introduce [OH −] = K w /[H +].
The strength of a weak acid is quantified by its acid dissociation constant, value. The strength of a weak organic acid may depend on substituent effects. The strength of an inorganic acid is dependent on the oxidation state for the atom to which the proton may be attached. Acid strength is solvent-dependent.