A. no of moles of HF = W/G.M.Wt
                                 Â
= 16.5/20Â Â = 0.825moles
molarity of
HFÂ Â Â Â Â Â Â Â Â Â Â
= no of moles /volume in L
                                Â
= 0.825/0.125Â Â = 6.6 M
no of moles of NaFÂ Â Â = 22/42 = 0.524moles
molarity of
NaFÂ Â Â Â Â Â Â Â Â =
0.524/0.125 = 4.192
        Â
PHÂ Â Â Â Â Â Â Â Â Â Â Â Â Â
= Pka + log[NaF]/[HF]
                             Â
= 3.17 + log4.192/6.6
                             Â
= 3.17-0.1971 = 2.9729
part-B
    no of moles of CH3NH2 = 1.23/31 =
0.03967 moles
    no of moles of CH3NH3Br  =
1.3/112 = 0.0116moles
      POH = Pkb +
log[CH3NH3Br]/[CH3NH2]
               Â
= 3.3665 + log0.0116/0.03967
               Â
= 3.3665-0.534 = 2.8325
    PH  = 14-POH
          =
14-2.8325Â Â = 11.1675
