Equilibrium - Result Question 75

####79. The dissociation constant of a weak acid is 1×104. In order to prepare a buffer solution with a pH =5 the [Salt]/[Acid] ratio should be

(a) 1:10

(b) 4:5

(c) 10:1

(d) 5:4

[NEET Kar. 2013]

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Solution:

  1. (c) Given, Ka=1×104

pKa=log(1×104)=4

Now from Handerson equation

pH=pKa+log[ Salt ][ Acid ]

Putting the values

5=4+log[ Salt ][ Acid ]

log[ Salt ][ Acid ]=54=1

Taking antilog

[Salt]/[Acid] =10=10:1



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