Salt Dissolution Problems [ENDORSED]
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Salt Dissolution Problems
Postby Andrew Wang 1K » Sun Jan 29, 2023 9:27 pm
For most salt dissolution (buffer solution) problems one of the ions will have no impact on the pH. How do you solve cases where both dissolved ions, from a salt like ammonium floride, impact pH?
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Re: Salt Dissolution Problems [ENDORSED]
Postby Chem_Mod » Sat Feb 04, 2023 10:05 pm
We don't make buffers using a different weak acid and weak base.
In your salt, ammonium fluoride, it would be formed from the weak base NH3, and the weak acid HF.
Solving for the pH with a salt like that is complicated as one has to set up two equilibria, one for the weak base and another for the weak acid.
Not suitable for general chemistry. :-)
Same reason why titrations are not done with a weak acid and weak base.
Titrations are always:
Strong acid and strong base.
Or
Strong acid and weak base.
Or
Weak acid and strong base.
If one does not know if the sample is a strong acid/base, then always use a titrant that is a strong acid or strong base.
Nice question Andrew.
In your salt, ammonium fluoride, it would be formed from the weak base NH3, and the weak acid HF.
Solving for the pH with a salt like that is complicated as one has to set up two equilibria, one for the weak base and another for the weak acid.
Not suitable for general chemistry. :-)
Same reason why titrations are not done with a weak acid and weak base.
Titrations are always:
Strong acid and strong base.
Or
Strong acid and weak base.
Or
Weak acid and strong base.
If one does not know if the sample is a strong acid/base, then always use a titrant that is a strong acid or strong base.
Nice question Andrew.
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