Weak Acids

*
*

Why space acids weak or strong?

Every mountain reacts v water. Once it loser a proton, it transfers that proton come water. Water acts together a base once it solvates the proton. The conjugate acid is protonated water and also it is represented as (H3O)+, (H5O2)+, (H2nOn)+, or simply as H+(aq). The conjugate base is the acid minus that is proton.A solid acid is fully dissociated in water while a weak mountain is in equilibrium v its conjugate base in water. Let"s look in ~ the reaction of a strong acid, nitric acid or HNO3, and a weaker acid, nitrous acid or HNO2, in water.

You are watching: Strong acid has a weak conjugate base

*
Nitric mountain is a more powerful acid 보다 nitrous acid because its conjugate basic is an ext stable. The NO3- ion has excess an adverse charge spread out end 3 oxygen atoms while the excess an adverse charge in NO2- is spread out out over on 2 oxygen atoms.A conjugate base is more stable once the an adverse charge is on one electronegative element and also when the charge is delocalized over multiple atoms. The an ext stable the conjugate base, the more powerful the acid. A stable conjugate base is not really basic. A very solid acid has a an extremely weak conjugate base and also a an extremely weak acid has actually a very strong conjugate base.

Weak acid Equilibrium

Nitrous mountain is in equilibrium v a proton and its conjugate base, NO2-. Because the concentration of water is constant, we can define a continuous equal to the product of the concentration of water and also the equilibrium constant. This constant, the Ka is 10-3.29 because that HNO2.
*
We have the right to use the Ka to recognize the pH the a systems of nitrous acid. Because that example, let"s recognize the pH that a solution made native 0.01 mole the HNO2 in 1.0 together of water. Some of the acid will dissociate right into H+ and NO2- yet we don"t recognize w=how much. We"ll contact the molar concentration that solvated protons x therefore = x. This means that the concentration that NO2- must additionally be x since they form in equal amounts by the dissociation that the acid. The concentration
*
It is always possible to deal with for x by using the quadratic equation but most of the moment we have the right to solve it utilizing an approximation. If we assume the the level of dissociation is small, then the equilibrium concentration of acid doesn"t change very much from its initial concentration. We have the right to then use the initial acid concentration in the Ka expression.The approximation is a an excellent one in this case due to the fact that we obtain the very same pH value utilizing it as we did from the quadratic equation.

See more: What Is The Most Important Inorganic Compound S Essential To Human Functioning?

Reaction in between Weak mountain and solid Bases

Strong bases react totally with weak bases to kind the conjugate base of the weak acid. Climate there will be one equilibrium in between the weak acid and its conjugate base in water. For example, let"s look at the solution developed by mixing 0.010 mol HNO2 and 0.004 mol NaOH in 1.0 together water. Again, we have the right to use an approximation to resolve this. The approximation is valid because the degree of dissociation will be small when there is currently some product present.
*

Weak mountain and strong Acids

The acid dissociation constants that a an option of mountain is in the tables. In the table are listed pKa values. pKa = -log(Ka)The very solid acids, those the are completely dissociated in water, are differentiated by examining their mountain dissociation equilibrium in non-aqueous solvents and the pKa because that water is estimated. The equilibrium constants for the weaker mountain (pKa >0) are established from pH dimensions of solutions.BackCompassIndexTablesIntroductionNextProfessor Patricia Shapley, university of Illinois, 2011