i need help with finding the ph of a buffer solution initially consisting of 0.0400 moles NH3 and 0.025 moles NH4^+ and 20 ml 0.75 NaOH.
ka of NH+4 = 5.6 ×10^-10
To calculate the pH of a buffer solution, you need to consider the equilibrium that exists between the weak acid (NH3) and its conjugate base (NH4+). The Henderson-Hasselbalch equation is commonly used for this calculation:
pH = pKa + log([A-]/[HA])
In this case, NH4+ is the weak acid (HA) and NH3 is the conjugate base (A-). However, before we can use this equation, we need to determine the concentrations of NH4+ and NH3 in the solution.
Given:
moles NH3 = 0.0400
moles NH4+ = 0.025
volume of NaOH solution = 20 mL = 0.020 L
First, find the molar concentration of NH3 and NH4+:
Concentration of NH3 = moles NH3 / volume of solution
Concentration of NH3 = 0.0400 / 0.020 = 2.00 M
Concentration of NH4+ = moles NH4+ / volume of solution
Concentration of NH4+ = 0.025 / 0.020 = 1.25 M
Now that we know the concentrations, we can use the Henderson-Hasselbalch equation to calculate the pH:
pKa = -log(Ka) = -log(5.6 × 10^-10) = 9.25
pH = 9.25 + log([NH3]/[NH4+])
pH = 9.25 + log(2.00/1.25)
pH ≈ 9.25 + 0.301
pH ≈ 9.55
So, the pH of the buffer solution is approximately 9.55.