A buffer solution is 1.00 M in NH3 and 1.10 M in NH4Cl. If 0.230 moles of NaOH are added to 1.00 L of the buffer, what is its pH? Assume the volume remains constant. Kb of NH3 = 1.8 multiplied by 10-5.
Use the Henderson-Hasselbalch equation.
NH3 + H^+ ==> NH4^+
initial:
NH3 = 1.00 M from the problem.
H^+ = whatever, but can be calculated if you want to know.
NH4^+ = 1.10 M from the problem.
Just for the fun of it I plugged in 1.00 for B and 1.10 for acid and found pH = 9.21.
For the problem, if we add 0.230 moles NaOH, we must REMOVE 0.230 H^+, which shifts the above equilibrium to the left. NH4^+ is decreased by 0.230 and NH3 is increased by 0.230.
Final moles NH3 = 1.00 + 0.230 = ??
Final moles NH4^+ = 1.10 - 0.230 = ??
Substitute into HH equation and solve. I get something close to 9.4 but check me out.
To find the pH of the buffer solution after NaOH is added, we need to determine the new concentration of NH3 and NH4+ in the solution. We can then calculate the concentration of OH- in the solution and use that to find the pOH and pH.
Let's break down the steps to solve this problem:
Step 1: Calculate the change in moles of NH3 and NH4+ when NaOH is added.
NaOH and NH3 react in a 1:1 ratio according to the balanced equation:
NH3 + NaOH → NH4+ + OH-
Since the initial moles of NaOH added to the buffer solution are given as 0.230 moles, the moles of NH3 and NH4+ will each increase by 0.230 moles.
Step 2: Calculate the new concentration of NH3 and NH4+.
To find the new concentration, we divide the moles of NH3 and NH4+ by the total volume of the buffer solution, which remains constant at 1.00 L.
concentration of NH3 = (moles of NH3 added) / (total volume of buffer) = 0.230 moles / 1.00 L = 0.230 M
concentration of NH4+ = (moles of NH4+ added) / (total volume of buffer) = 0.230 moles / 1.00 L = 0.230 M
Step 3: Calculate the concentration of OH-.
Since NH4+ reacts with OH- to form water, the number of moles of OH- equals the number of moles of NH4+.
concentration of OH- = concentration of NH4+ = 0.230 M
Step 4: Calculate the pOH.
pOH is calculated by taking the negative logarithm (base 10) of the OH- concentration. In this case, pOH = -log10(0.230).
pOH = -log10(0.230) ≈ 0.638
Step 5: Calculate the pH.
The pH can be determined using the equation pH + pOH = 14.
pH + 0.638 = 14
pH = 14 - 0.638 = 13.362
Therefore, the pH of the buffer solution after adding 0.230 moles of NaOH is approximately 13.362.