Can the NH3/NH4Cl system be sued to prepare a buffer of a pH 9.5? why or why not? Can it prepare a buffer of pH 5? There were two buffers, 0.2 M and 0.1M.
Thank you, it should say 'used' not 'sued'.
To determine whether the NH3/NH4Cl system can be used to prepare a buffer of pH 9.5, we need to consider the acid-base equilibrium involved in this system.
NH3 (ammonia) is a weak base, and NH4Cl (ammonium chloride) is its corresponding conjugate acid. In an aqueous solution, NH3 will accept a proton (H+) from water to form NH4+ and OH-, while NH4Cl will dissociate into NH4+ and Cl-.
The equation for the reaction between NH3 and H2O is as follows:
NH3 + H2O ⇌ NH4+ + OH-
To determine the pH of the buffer system, we need to consider the equilibrium constant, Kb, which represents the strength of NH3 as a base. The pKb is the negative logarithm (base 10) of Kb.
If the pKb of NH3 is less than the desired pH, the NH3/NH4Cl system can be used to prepare a buffer at that pH. On the other hand, if the pKb is greater than the desired pH, it is not suitable for preparing a buffer at that pH.
Now, let's calculate the pKb for NH3:
Kb = [NH4+][OH-]/[NH3]
Given that the concentration of NH4Cl is 0.2 M or 0.1 M, we can assume that the concentration of NH4+ and Cl- is also equal to 0.2 M or 0.1 M, respectively.
Let's consider the 0.2 M NH4Cl solution as an example:
Kb = [NH4+][OH-]/[NH3]
= (0.2)(x)/(0.2-x) [Assuming the concentration of NH3 is x]
Since NH4Cl is a strong electrolyte, it fully dissociates into NH4+ and Cl-. Therefore, the concentration of NH4+ is equal to the concentration of NH4Cl, which is 0.2 M.
Kb = (0.2)(x)/(0.2-x)
To prepare a buffer of pH 9.5, we need to calculate the pKb of NH3 (pKb = -log10Kb) and compare it with pH 9.5.
If pKb < 9.5, the NH3/NH4Cl system can be used to prepare a buffer of pH 9.5. If pKb > 9.5, it is not suitable.
To determine if the NH3/NH4Cl system can prepare a buffer of pH 5, we need to apply the same process. Calculate the pKb of NH3 and compare it with pH 5.
Note: The pKb for NH3 is approximately 4.75, which means NH3/NH4Cl cannot be used to prepare a buffer of pH 9.5 or pH 5.
I don't know how we can sue the NH3/NH4Cl system; however, the pKa for NH3 is 9.25 and that is within the range. What about the two buffers of 0.2M and 0.1M?
9.5 yes.
5 no.