conside following data on some weak acids and weak bases: acid base name formula

Question

conside following data on some weak acids and weak bases: acid base name formula name formula acetic acid HCH3CO21.8 x10 methylamine CH3NH2 | 4.4 × 10- nitrous acid HNO 2 4.5 x 10 pyridine CHN 1.7x10 Ar Use this data to rank the following solutions in order of increasing pH. In other words, select a '1' next to the solution that will have the lowest pH, a '2" next to the solution that will have the next lowest pH, and so on solution pH 0.1 M KCH3CO2 0.1 M NaNO2 0.1 M C5HsNHCI choose one I choose one 4 (highest) 0.1 M KBr choose one

Explanation / Answer

1) pH of KCH3CO2 = 7+1/2(pka+logC)

pka of CH3COOH = -log(1.8*10^-5) = 4.74

                 = 7+1/2(4.74+log0.1)

               pH = 8.87

2) NaNO2

    pka of HNO2 = -log(4.5*10^-4) = 3.35

   pH of NaNO2 = 7+1/2(pka+logC)

                = 7+1/2(3.35+log0.1)

                = 8.175

3) C5H5NHCl

   pkb = -log(1.7*10^-9) = 8.77

pH = 7-1/2(pkb+logC)

     = 7-1/2(8.77+log0.1)

     = 3.115

4)   KBr ,

   pH = 7

priority order

KCH3CO2 = 4 (highest)

NaNO2 = 3

C5H5NHCl = 1

KBr = 2

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