Question #d9358
1 Answer
!! VERY LONG ANSWER !!
To solve this problem, you'll need the value of the base dissociation constant,
Moreover, you're going to be dealing with a buffer that consists of a weak base, ammonia, and its conjugate acid, ammonium chloride,
Calculate the
Now you're good to go. in order, the pH of the solution at various points in the titration will be
- Before adding
#HCl#
Since ammonia is a weak base, you can expect the pH of the solution to be basic, or greater than 7. An equilibrium will be established that will allow you to calculate the concentration of the hydroxide ion,
I........0.1..........................................0................0
C.....(-x)..........................................(+x).............(+x)
E.....0.1-x.........................................x.................x
By definition, the acid dissociation constant will be
Because
Calculate the solution's pOH by
As a result, the pH will be
- After the addition of 10 mL of
#HCl#
Now you start adding acid to the solution. Ammonia will react with the strong acid to produce ammonium chloride, which will act as the conjugate acid
The net ionic equation is
Calculate the number of moles of ammonia you initially had in solution
The number of moles of hydrochloric acid added will be
All the acid
The volume of the solution will now be
The concentrations of ammonia and ammonium chloride will be
The pOH of the solution will be
- After half of the ammonia has been neutralized
When half of the ammonia is neutralized, the number of moles of ammonia that remanin in solution will be equal to the number of moles of ammonium chloride produced.
Since the volume is always the same for both species, this implies that
- At the equivalence point
At the equivalence point, all the ammonia has been consumed by the strong acid. This implies that ammonium chloride will be the only species left in solution.
Moreover, the number of moles of ammonium chloride produced will be equal to the initial number of moles of ammonia, 0.0025.
The total volume of the solution will be
The molarity of the ammonium chloride will be (because the ammonia solution and the hydrochloric acid solution had equal molarities)
The following equilibrium will be established
I.....0.05.........................................0.................0
C.....(-x)..........................................(+x)..............(+x)
E....0.05-x......................................x..................x
This time, use the acid dissociation constant,
Solving for
Therefore, the final pH of the solution will be