Question

What mass of solid K2CO3 (molar mass = 138.0 g/mol) should be added to 0.941 L of 0.480 M HCO3– to make a buffer with a pH of 10.32? (pKa of HCO3– = 10.32)

Answer 1

pH of acidcbuffer = pka + log(salt/acid)

   pKa of HCO3– = 10.32

no of mole of salt = k2co3 = ?

no of mol of HCO3- = M*V

                                       = 0.48*0.941 = 0.452 mol

10.32 = 10.32+log(x/0.452)

x = 0.452

no of mole of salt = k2co3 = x = 0.452 mol

mass of k2co3 must be added = n*Mwt

                          = 0.452*138

                      = 62.376 g