Question

0.1 mole of sodium formate was added to one litre of 0.2 M solution of
formic acid (Ka = 1.8 x 10^-4). How will the H+ concentration of the acid diminish
assuming the salt to be completely dissociated?​

Answer 1

Answer:

Correct option is

A

4

HCOOH →

 HCOO−   +         

H+

Initial concentration (M)

        0.2

6.4×10−3

6.4×10−3Equilibrium concentration (M)

       0.2+x16.4×10−3−x

K=[HCOOH][HCOO−][H+]=0.2+x6.4×10−3−x=2.4×10−4 

⟹x=0.00635

[H+]=6.4×10−3−0.00635

=4.9×10−5

pH=−log[H+]

=−log 4.9×10−5=4.305

Hence, the answer to the nearest integer is 4.

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Answer 2

Answer:

H+ will diminish by 1/16.6 of its original value.