The resulting pH of a solution when 100 mL of 0.877 M NH3 is mixed with 100 mL of 0.481 M HBr is ___. For NH3, Kb = 1.8 × 10−5.
See your other post. NH is the base. Remember to change Kb to pKa.
9.54 for this one?
Check your work. I found 9.52. I used 9.26 for pKa.
14-4.74 = 9.26
To find the resulting pH of the solution when NH3 and HBr are mixed, we can use the concept of acid-base reactions and the principles of equilibrium.
Step 1: Write the balanced chemical equation for the reaction between NH3 and HBr.
NH3 + HBr → NH4+ + Br-
Step 2: Determine the limiting reactant. To do this, we compare the number of moles of each reactant.
Given that the volume of both solutions is the same (100 mL each), we can use the formula:
moles = concentration (M) × volume (L)
For NH3:
moles of NH3 = 0.877 M × 0.100 L = 0.0877 moles
For HBr:
moles of HBr = 0.481 M × 0.100 L = 0.0481 moles
Since NH3 has a higher number of moles, it is the excess reactant. Therefore, HBr is the limiting reactant.
Step 3: Calculate the reaction between HBr and NH3. Here, HBr acts as an acid, donating a proton (H+) to NH3, which acts as a base.
HBr + NH3 → NH4+ + Br-
Step 4: Calculate the number of moles of NH4+ formed. Since the reaction is 1:1 between HBr and NH4+, the number of moles of NH4+ formed is equal to the moles of HBr used.
moles of NH4+ = moles of HBr = 0.0481 moles
Step 5: Calculate the concentration of NH4+ in the resulting solution. Since the total volume is 200 mL (100 mL NH3 + 100 mL HBr), we need to convert it to liters.
Total volume = 200 mL = 200 mL × (1 L / 1000 mL) = 0.20 L
concentration of NH4+ = moles of NH4+ / total volume
concentration of NH4+ = 0.0481 moles / 0.20 L = 0.2405 M
Step 6: Calculate the concentration of NH3 in the resulting solution.
For every mole of NH4+ formed, one mole of NH3 reacts. So, the concentration of NH3 will be the initial concentration minus the concentration of NH4+ formed.
initial concentration of NH3 = 0.877 M
concentration of NH3 = initial concentration of NH3 - concentration of NH4+
concentration of NH3 = 0.877 M - 0.2405 M = 0.6365 M
Step 7: Calculate the pOH of the solution. Since NH3 is a weak base, it reacts with water to produce OH- ions. The concentration of OH- ions can be determined from the reaction with NH3 and the value of Kb.
NH3 + H2O → NH4+ + OH-
Kb = [NH4+][OH-] / [NH3]
0.2405 * x / 0.6365-x = 1.8 * 10^-5
Solving this equation, we find that x = 0.0040 M
Step 8: Calculate the pH of the solution using the pOH value. The pH is determined by the equation:
pH = 14 - pOH
pH = 14 - (-log10(0.0040))
Simplifying, we find that the pH of the resulting solution is 11.4.