Use the Henderson-Hasselbalch equation to calculate the pH of each solution: 1)

Question

Use the Henderson-Hasselbalch equation to calculate the pH of each solution:
1) a solution that is 0.180 M in HC2H3O2 and 0.115 M in KC2H3O2
2) a solution that is 0.190 M in CH3NH2 and 0.110 M in CH3NH3Br

Calculate the pH of the solution that results from each of the following mixtures.
1) 150.0 mL of 0.26 M  HF with 220.0 mL of 0.31 M  NaF
2) 175.0 mL of 0.12 M C2H5NH2 with 285.0 mL of 0.22 M C2H5NH3Cl

A 35.0 mL sample of 0.118 M HNO2 is titrated with 0.294 M KOH. (Ka for HNO2 is 4.57×104.)
Determine the pH at the equivalence point for the titration of HNO2 and KOH.

Explanation / Answer

1) pH of acidc buffer = pka + log(salt/acid)

       pka of CH3COOH = 4.74

= 4.74+log(0.115/0.18)

= 4.54

2) pOH basebuffer = pkb+log(salt/base)

   pkb of CH3NH2 = 3.38

   = 3.38 + log(0.11/0.19)

    = 3.14

pH = 14-3.14 = 11.86

1) pH of acidc buffer = pka + log(salt/acid)

       pka of HF = 3.17

concentration of HF = 150/370*0.26 = 0.105 M

concentration of NaF = 220/370*0.31 = 0.184 M

= 3.17+log(0.184/0.105)

= 3.413

2) pOH basebuffer = pkb+log(salt/base)

concentration of C2H5NH2 = 175/460*0.12 = 0.046 M

concentration of NaF = 285/460*0.22 = 0.136 M

  
   pkb of C2H5NH2 = -log(4.3*10^(-4)) = 3.37

   = 3.37 + log(0.136/0.046)

    = 3.84

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