Question

In: Chemistry

Calculate the pH if 0.03 mol HCl is added to 0.500 L of a buffer solution...

Calculate the pH if 0.03 mol HCl is added to 0.500 L of a buffer solution that is 0.24 M NH3 and 0.20 M NH4Cl?

For NH3 Kb= 1.8 x 10-5

Solutions

Expert Solution

no of moles of NH3 = molarity * volume in L

                               = 0.24*0.5    = 0.12 moles

no of moles of NH4Cl   = molarity * volume in L

                                      = 0.2*0.5    = 0.1 moles

PKb   = -logKb

         = -log1.8*10^-5

         = 4.75

POH   = PKb + log[NH4Cl]/[NH3]

          = 4.75 + log0.1/0.12

         = 4.75-0.0791

         = 4.6709

By the addition of 0.03 moles of HCl

no of moles of NH3 after addition of 0.03 moles of HCl   = 0.12-0.03   = 0.09 moles

no of moles of NH4Cl after addition of 0.03 moles of HCl   = 0.1+0.03   = 0.13 moles

POH   = PKb + log[NH4Cl]/[NH3]

          = 4.75 + log0.13/0.09

        = 4.75 + 0.1597   = 4.9097

PH   = 14-POH

        = 14-4.9097   = 9.0903

       


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