Although the dissociation of an acid is commonly written as indicated in Kw=[H+]

Question

Although the dissociation of an acid is commonly written as indicated in Kw=[H+][OH-] = 1.0 E -14, better representations of the process and the resulting equilibrium expression are:

HA(aq) + H20(l) = H3O+ + A- K=[H3O+][A-]/[HA][H2O]

The equilibrium expression is usually simplified to Ka=[H+][A-]/[HA] by multiplying both sides of the equation by the concentration of water and defining a new constant, the acid dissociation constant, Ka as [K][H2O].

Is it a valid procedure to incorporate the water concentration into the acid dissociation constant?

Explanation / Answer

Yes it is a better approximation since the solvent is water and the amount of water remains almost costant because the amount of water produced in this reaction is very small as compared to total water concentration of water present as solvent therefore [H2O]*K=ka another constant

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