What concentration of ammonia, [NH3], should be present in a solution with [NH4+]= 0.734M to produce a buffer solution with pH= 9.13? For NH3, Kb= 1.8x10^-5
Your posts have been removed because of your "homework dumping" -- a string of posts in quick succession with absolutely no sign that you have given any thought to anything.
Once you write up YOUR THOUGHTS, please re-post, and someone here will be happy to comment.
NH3 + H2O ==> NH4^+ + OH^
Kb = (NH4^+)(OH^-)/(NH3)
Convert pH to pOH, then to (OH^-), substitute into Kb. Also substitute into Kb what you want the (NH4^+) to be and solve for (NH3).
To determine the concentration of ammonia, [NH3], required to produce a buffer solution with a pH of 9.13, we can use the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
In this case, ammonia (NH3) acts as the base (A-) and ammonium (NH4+) acts as the acid (HA). The pKa is determined using the Kb value provided, which is the equilibrium constant expression for the base dissociation:
Kb = [NH3][OH-]/[NH4+]
Given that Kb = 1.8x10^-5, we can determine the pKa from this value:
Kw = Ka * Kb
where Kw is the ion product of water, equal to 1.0x10^-14 at 25°C.
1.0x10^-14 = 1.0x10^-14 = Ka * 1.8x10^-5
Solving for Ka:
Ka = Kw / Kb = (1.0x10^-14) / (1.8x10^-5) = 5.56x10^-10
Now we can calculate the ratio of [A-]/[HA] using the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
9.13 = -log (5.56x10^-10) + log ([A-]/[HA])
Rearranging the equation:
log ([A-]/[HA]) = 9.13 + log (5.56x10^-10)
Calculating the term on the right side:
log ([A-]/[HA]) ≈ 9.13 + (-9) = 9.13 - 9 ≈ 0.13
Next, we can use logarithmic properties to solve for the ratio [A-]/[HA]:
[A-]/[HA] = 10^0.13
[A-]/[HA] = 1.37096
Since [A-] is the concentration of ammonia, [NH3], and [HA] is the concentration of ammonium, [NH4+], we can let [NH4+] be 0.734 M.
1.37096 = [NH3] / 0.734
Solving for [NH3]:
[NH3] ≈ 1.37096 * 0.734
[NH3] ≈ 1.00431 M
Therefore, the concentration of ammonia, [NH3], that should be present in the solution is approximately 1.004 M.
To determine the concentration of ammonia, [NH3], in the buffer solution with a given pH, we need to apply the Henderson-Hasselbalch equation. The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa (negative logarithm of Ka) and the ratio of the concentrations of the conjugate acid and base pair.
In this case, we are given the pH and the concentration of NH4+ (the conjugate acid), so we need to find the concentration of NH3 (the conjugate base) to calculate the ratio.
Step 1: Convert the pH to pOH
pOH = 14 - pH
pOH = 14 - 9.13
pOH = 4.87
Step 2: Calculate the concentration of OH- using pOH
pOH = -log[OH-]
10^(-pOH) = [OH-]
10^(-4.87) = [OH-]
[OH-] = 1.28 x 10^(-5) M
Step 3: Calculate the concentration of NH3 using Kb, [OH-], and the concentration of NH4+
Kb = [NH3][OH-] / [NH4+]
1.8 x 10^(-5) = [NH3] * (1.28 x 10^(-5)) / 0.734
[NH3] = (1.8 x 10^(-5) * 0.734) / (1.28 x 10^(-5))
[NH3] = 1.038 M
Therefore, the concentration of ammonia, [NH3], should be 1.038 M to produce a buffer solution with a pH of 9.13, with [NH4+] = 0.734 M.