Ionisation Constants of HF & Its CB: Why 10-14?

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In summary, the ionisation constant (IC) of the conjugate base of HF is equal to the reciprocal of the ionisation constant of HF multiplied by the ionic product of water. This can also be referred to as the basicity constant (Kb) or hydrolysis constant.
  • #1
chound
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If 6.8 * 10-4 is ionisation constant(IC) of HF, what is the IC of its conjugate base.

HF +H2O -----> H3O+ +F-
So F- is the conjugate base(CB)
I figured the IC of CB would be the reciprocal of IC of HF. But the answer given is the same but multiplied by Ionic product of water i.e. 10-14

Please explain why
 
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  • #2
Ionisation of the conjugate base? Isn't it already ionised?

Perphaps you mean the basicity constant for the equilibirium
F- + H2O ----> HF + OH-

In that case, won't it be Kw/Ka?
 
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  • #3
yep, that's what is meant the ionization constant, in this problem. For the base it can also be called the hydrolysis constant, Kb
 

1. What is the significance of the ionization constant of HF being 10^-14?

The ionization constant of HF being 10^-14 is significant because it represents the equilibrium constant for the ionization reaction of HF into its constituent ions, H+ and F-. This value is a reflection of the strength of the acid, with a lower value indicating a stronger acid.

2. How is the ionization constant of HF related to its conjugate base?

The ionization constant of HF is also known as the acid dissociation constant (Ka) and it is related to its conjugate base (F-) through the equation Ka x Kb = Kw, where Kb is the base dissociation constant and Kw is the auto-ionization constant of water. This relationship allows for the calculation of the Kb value from the known Ka value.

3. What factors can affect the ionization constant of HF?

The ionization constant of HF can be affected by factors such as temperature, presence of other ions or molecules in solution, and the solvent used. Temperature can affect the equilibrium constant by changing the energy required for the ionization reaction, while the presence of other ions or molecules can shift the equilibrium and alter the equilibrium constant.

4. How can the ionization constant of HF be determined experimentally?

The ionization constant of HF can be determined experimentally through titration methods, where a known concentration of HF is titrated with a strong base, such as NaOH, and the resulting pH is measured. The pH at the equivalence point can be used to calculate the Ka value using the Henderson-Hasselbalch equation.

5. What is the relationship between the ionization constant of HF and its acid strength?

The ionization constant of HF is directly related to its acid strength, with a lower Ka value indicating a stronger acid. This is because a stronger acid will have a higher tendency to donate a proton, resulting in a higher concentration of H+ ions in solution and a lower pH. Therefore, the ionization constant can be used as a measure of acid strength for HF and other weak acids.

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