25. A buffer is prepared by mixing picric acid and its conjugate base in a 2:1 ratio. The pH of the solution is measured as 0.079. What is the Ka of picric acid?

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Answer 1 · 2018-02-22T15:32:51

#K_a = 0.417#

Equation for the pH of week acid is:

#pH = pK_a + log [A^-/{HA}]#

where #A^-# is the concentration of conjugate base.

#HA# is the concentration of Acid.

# #
# #
# #

#pH = 0.079# #" "##\color(blue){\rightarrow}# #\text{Given}#

#0.079 = pK_a + log [1/2]#

# #
# #

#0.079 = pK_a -0.3#

#pK_a = 0.079 + 0.3#

#pK_a = 0.38#

# #
# #

Use the equation #\ \ \ # #K_a= 10^{-pK_a}# #\ \ \ # to calculate the #K_a# of picric acid.

#K_a = 10^{-0.38}#

#K_a = 0.417#