what is the ph of 0.4M NH3 and 0.36M NH4CL buffer system? and the pH after adding 20mL of 0.05 NaOH to 80mL of the buffer solution
To determine the pH of a buffer solution, you need to consider the dissociation of the weak acid and its conjugate base. In this case, NH3 acts as the weak base and NH4Cl as its conjugate acid.
Step 1: Calculate the pKa of the weak acid (NH4Cl). The pKa value can be found in a chemistry reference book or online database. For NH4Cl, the pKa is 9.24.
Step 2: Calculate the initial concentrations of NH3 and NH4Cl.
Given:
- NH3 concentration = 0.4 M
- NH4Cl concentration = 0.36 M
Step 3: Determine the amount of NH4+ and OH- ions formed when NH4Cl dissociates in water.
NH4Cl → NH4+ + Cl-
Step 4: Calculate the concentration of NH4+ and NH3 after the NH4Cl dissociation.
Given:
- NH4Cl concentration = 0.36 M
- NH4+ concentration = 0.36 M (since one NH4+ ion is formed for every NH4Cl molecule)
Step 5: Calculate the concentration of OH- ions after adding 20 mL of 0.05 M NaOH to 80 mL of the buffer solution.
Concentration of OH- ions = (0.05 M * 0.02 L) / (0.08 L + 0.02 L)
Step 6: Calculate the concentration of NH3 and NH4+ ions after the addition of NaOH.
Since NH3 acts as a base, it will react with OH- ions to form NH4+ ions and water.
Step 7: Calculate the new concentrations of NH3 and NH4+ ions.
Given:
- Initial NH3 concentration = 0.4 M
- Initial NH4+ concentration = 0.36 M
- Concentration of OH- ions = Calculated value from Step 5
Step 8: Calculate the new pH of the buffer solution.
pH = pKa + log( [NH4+]/[NH3] )
Now that we have all the necessary calculations, we can determine the pH of the buffer solution in Question 1 and the pH after adding NaOH in Question 2.