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Calculate the pH of a 1.40×10-1 M aqueous solution of hydrazine hydrochloride (H2NNH3Cl).

(For hydrazine, H2NNH2Kb = 3.00×10-6.)

Feb 14th, 2015

H2NNH3+        =>    H2NNH2     +       H+      ;     Ka = Kw/Kb = (10^-14)/(3.00*10^-6)   = 3.34 * 10^-9

   0.140                           0                      0 

      -x                             +x                     +x

 (0.140-x)                      (x)                     (x)  


Ka = (3.34*10^-9) = (x^2) / (0.140-x)      

Rearrange and quadratic formula gives    =>   x = 2.16 * 10^-5 M 

pH = -log(2.16*10^-5) = 4.7 

Feb 14th, 2015

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