In: Chemistry
What is the pH of a buffer prepared by mixing 20.00 mL of 0.0300 M ammonium chloride with 40.00 mL of 0.0450 M ammonia? What is the resulting pH if 1.00 mL of 0.10 M HCl is added to this solution?
no of moles of NH4Cl = molarity * volume in L
= 0.03*0.02 = 0.0006moles
no of moles of NH3 = molarity * volume in L
= 0.045*0.04 = 0.0018moles
POH = PKb + log[NH4Cl]/[NH3]
= 4.75 + log0.0006/0.0018
= 4.75-0.4771 = 4.2729
PH = 14-POH
= 14-4.2729 = 9.7271
By the addition of HCl
no of moles of HCL = molarity * volume in L
= 0.1*0.001 = 0.0001moles
no of moles of NH4Cl = 0.0006+0.0001 = 0.0007moles
no of moles of NH3 = 0.0018-0.0001 = 0.0017 moles
POH = PKb + log[NH4Cl]/[NH3]
= 4.75 + log0.0007/0.0017
= 4.75-0.3853 = 4.3647
PH = 14-4.3647 = 9.6353