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Acid/Base Problem

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bewitchedsw:
We were asked to predict whether a list of salts were acidic or basic given their parent acids and bases.  I predicted that HCl + NH4OH ---> NH4Cl + H2O would yeild a ACIDIC salt, since HCl is a strong acid and NH4OH is a very weak base.  We tested the NH4OH salt solution (diluted into water) and the solution was neutral.

Why was the solution neutral and not acidic?

My guesses:

The HCl was dated 1987...Can it weaken over time?
The water somehow weakened the HCl?
Anytime a salt is produced, it is neural?

The assignment is due tomorrow and I only have to guess at the cause.  These are my guesses, I am looking for ways to prove them to myself.  I am going further in chemistry (dental school candidate) so I really WANT to understant this.  Am I on the right track with any of my guesses?

Sam

Mitch:
No doubt it was suppose to make an acidic salt. Did you use enough HCl in the reaction? What was the molarity of HCl and NH4OH?

bewitchedsw:
Our instructions in our lab book said "a 1.00g sample of the salt in 5.00 mL of distilled water." However, we were instructed in the lab to use a "scoop" (not very scientific, but this is an introductory class) of a NH4Cl salt and fully dissolve it in distilled water.  We used ~1tbsp and it took a good 1/2 to 3/4 cup of water to fully dissolve it.  So, I don't know how many moles we used or what the mass was.  Do you think it had to do with the concentration of the NH4Cl in the water?

Thanks for your *delete me*

Donaldson Tan:

--- Quote from: bewitchedsw on April 13, 2004, 01:47:03 PM ---We were asked to predict whether a list of salts were acidic or basic given their parent acids and bases.  I predicted that HCl + NH4OH ---> NH4Cl + H2O would yeild a ACIDIC salt, since HCl is a strong acid and NH4OH is a very weak base.  We tested the NH4OH salt solution (diluted into water) and the solution was neutral.

--- End quote ---
U were instructed to add aq HCl to aq NH3 i suppose. aq NH3 is a weak alkali and aq HCl is a strong acid. Such combination should yield an acidic salt NH4Cl. That suggests that the final solution should be slightly acidic (after-all NH4+ isnt a strong acid).


--- Quote from: bewitchedsw on April 13, 2004, 01:47:03 PM ---The HCl was dated 1987...Can it weaken over time?
The water somehow weakened the HCl?

--- End quote ---
The strength of an acid is dependent on the extent of its dissociation. A strong acid dissociates completely, eg. HCl dissociates completely to yield H3O+ in solution.

Mitch:

--- Quote from: bewitchedsw on April 13, 2004, 03:20:16 PM ---Our instructions in our lab book said "a 1.00g sample of the salt in 5.00 mL of distilled water." However, we were instructed in the lab to use a "scoop" (not very scientific, but this is an introductory class) of a NH4Cl salt and fully dissolve it in distilled water.  We used ~1tbsp and it took a good 1/2 to 3/4 cup of water to fully dissolve it.  So, I don't know how many moles we used or what the mass was.  Do you think it had to do with the concentration of the NH4Cl in the water?

Thanks for your *delete me*

--- End quote ---

I think you used too much water. And whatever acididity you should of seen got very diluted with 3/4 cup of water.

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