A basic buffer is prepared by adding 0.3310g of NH4Cl to 1.00L of 0.2088 M NH3. Kb (NH3) = 1.8x10-5.
And you want to know the pH? Use the Henderson-Hasselbalch equation.
To answer this question, we need to calculate the pH of the buffer solution. The NH4Cl and NH3 form a conjugate acid-base pair in this buffer system, which helps to resist changes in pH.
Here's how you can calculate the pH of the buffer solution:
1. Calculate the moles of NH4Cl:
- Moles = mass / molar mass
- Given that the mass of NH4Cl is 0.3310g, and the molar mass of NH4Cl is 53.49 g/mol:
Moles = 0.3310g / 53.49 g/mol
2. Calculate the moles of NH3:
- Moles = concentration x volume
- Given that the concentration of NH3 is 0.2088 M (moles per liter), and the volume is 1.00 L:
Moles = 0.2088 M x 1.00 L
3. Calculate the total moles of NH3 and NH4Cl in the buffer solution:
Total moles of NH3 = moles of NH3
Total moles of NH4Cl = moles of NH4Cl
4. Calculate the concentrations of NH3 and NH4Cl:
- Concentration = moles / volume
- Concentration of NH3 = Total moles of NH3 / 1.00 L
- Concentration of NH4Cl = Total moles of NH4Cl / 1.00 L
5. Calculate the ratio of NH4Cl to NH3:
- Ratio = Concentration of NH4Cl / Concentration of NH3
6. Calculate the pKa of NH3:
- pKa = -log(Ka)
- Given that Kb (NH3) = 1.8x10^-5, and Kw (water) = 1.0x10^-14 (at 25°C):
Ka = Kw / Kb (since Kw = Ka x Kb)
Ka = (1.0x10^-14) / (1.8x10^-5)
pKa = -log(1.0x10^-14 / 1.8x10^-5)
7. Calculate the pH of the buffer solution:
- pH = pKa + log(base/acid)
- Given that log(base/acid) is the same as log(ratio):
pH = pKa + log(ratio)
Now, you can plug in the values and calculate the pH.