In this problem we will use the weak base ammonia (NH 3 ) and its conjugate acid
ID: 853943 • Letter: I
Question
In this problem we will use the weak base ammonia (NH3) and its conjugate acid NH4+
First, complete this reaction of NH3 when in water: NH3 + HOH _______ + _______
Next, show the chemical set up for the Kb of NH3:
Kb =[ ] [ ]
[ ]
Ammonia-ammonium buffers have wide applications, but an important one for us to consider is the system found in our kidneys (and other animals as well for those of you considering veterinary applications) where acidity can build up as urine is formed.
(1) Suppose in a biology study an ammonia buffer system was needed to maintain a pH level of 7.90.What would be the NH4+ to NH3 ratio needed in a 1.00 liter solution?
(A) First, determine the [OH-] molarity that would be present by converting pH to [OH-]
(show your work)
[OH-] = ______ M
(B) Now, determine the ammonium to ammonia ratio (use your Kb set up to solve for this) that would produce the desired 7.90 pH:
(The Kb value for ammonia = 1.8 x10-5)
=
(2) Now that you have the proper ratio of ammonium to ammonia in a 1.0 L solution, let
Explanation / Answer
NH3 + H2O ? NH4+ + OH -
Kb = [NH4+][OH -] / [NH3]
1) A) Given pH = 7.9 ; pOH = 6.1 therefore [OH -] = 10-6.1 = 7.94 *10-7
B) pOH = pKb + log [NH4+] / [NH3]
6.1= 4.74 + log [NH4+] / [NH3]
[NH4+] / [NH3] = 22.9
2) 1/10 th ratio = 22.9/10 = 2.29
NH3 + H + ------> NH4 +
2.29-0.01 0 2.29 +0.01
pOH = pKb + log [NH4+] / [NH3]
= 4.74 + log 2.3/2.28
=4.743 and pH = 9.257
[OH -] = 1.8 *10^-5
c) if concentrations are equal . pOH will be equal to pKb and pH = 14 - pKb
pH = 9.26
Related Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.