"<...> a weak mountain is one that only rarely dissociates in water <...>. Likewise, because the conjugate base is a weak base, <...>"

which seems to was standing in dispute with my assumption a) above. So, what is correct?

Furthermore, if b) is correct, isn"t any solution of a weak acid systems a buffer, since any type of weak mountain in water renders an equilibrium of the form

\$HA ext (weak acid) leftrightarrow H^+ + A^- ext (conjugate base)\$

and is therefore a systems of a weak acid and also its base?

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inquiry Jul 16 "16 at 15:58

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Your declare a) isn"t constantly true.

You are watching: Is the conjugate base of a weak acid a strong base

Water dissociation is represented by:

\$\$ceH2O + H2O H3O+ + OH-\$\$

\$\$ K_mathrm w=cdot = 1 imes 10^-14 ( extrmat 25^circ ~mathrm C) \$\$

Note 1: we don"t create the \$ceH_2O\$ activity, because it have the right to usually it is in rounded to 1 and the ions tasks can it is in rounded to your concentrations.

Note 2: This value was obtained experimentally, considering the concentration that \$ceH_3O^+\$ and \$ceOH^-\$ in the medium was the same and also measuring the ionization that water.

On a weak acid dissociation:

\$\$ceHA + H2O A- + H3O+\$\$

\$\$K_mathrm a=fraccdot \$\$

On that is conjugate base:

\$\$ceA- + H2O HA + OH-\$\$

\$\$K_mathrm b=fraccdot \$\$

If we "add" both reactions we mean that both equilibriums will happen in the mixture, so we have:

\$\$ceHA + H2O A- + H3O+ (K_mathrm a)\$\$

\$\$ce+\$\$

\$\$ceA- + H2O HA + OH- (K_mathrm b)\$\$

\$\$ce============================\$\$

\$\$ceH2O + H2O H3O+ + OH- (K_mathrm w)\$\$

\$\$K_mathrm bcdot K_mathrm a= cdot cdot (cdot )/( cdot ) = cdot = K_mathrm w\$\$

\$\$K_mathrm b=K_mathrm w/K_mathrm a~~~~~~ K_mathrm b=10^-14/K_mathrm a extrmat 25^circ ~mathrm C\$\$

Another means to create this:

eginalign-log(K_mathrm b)&=-log(10^-14K_mathrm a) \ implies mathrm pK_mathrm b &= -log(10^⁻14) - (-log(K_mathrm a))\ implies mathrm pK_mathrm a+mathrm pK_mathrm b &=14;.endalign

This is the relation in between a conjugate basic strength and also its mountain strength. A very strong acid has actually a weak conjugate base, but a weak mountain doesn"t necessarily have a very strong base. Speak you have actually a \$mathrm pK_mathrm a=5\$, i beg your pardon is a weak acid, through \$K_mathrm a=1 imes 10^-5\$. The conjugate base would have a \$mathrm pK_mathrm b=14-5=9\$ or a \$K_mathrm b=1 imes 10^-9\$, which is no a strong base.

However, if we have a strong acid, prefer \$ceHCl\$ with a \$mathrm pK_mathrm a=-6.3\$ and also \$K_mathrm a=10^6.3\$. Its conjugate base would have actually a \$mathrm pK_mathrm b=14-(-6.3)=20.3\$ and also \$K_mathrm b=10^-20.3\$ i m sorry is a yes, really weak base.

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Hopefully i didn"t do it even more confusing for you! It"s mostly an reaction equilibrium issue.