What is the PH of a 1M CH3COONa? Ka of acetic acid=1.8x10-5,Kw=10-14 mol2/l2

  • Option 1)

    2.4

  • Option 2)

    3.6

  • Option 3)

    4.8

  • Option 4)

    9.4

 

Answers (1)

As learnt in

Ionization constant of weak acids -

Consider 

HX(aq)+H_{2}O(l)\rightleftharpoons H_{3}O^{+}(aq)+\bar{X}(aq)
 

K_{a}=dissociation\:or\:ionization\:constant

- wherein

K_{a}=\frac{C^{2}\:\alpha ^{2}}{C(1-\alpha )}

K_{a}=\frac{C\alpha ^{2}}{1-\alpha }
 

C=initial\:concentration\:of\:undissociated\:acid

\alpha =extent\:upto\:which\:HX\:is\:ionized\:into\:ions.

 

 PH = 7-\frac{1}{2} p \:\: K_{a} - \frac{1}{2} log C

\Rightarrow PH = 7+\frac{1}{2} log (1.8\times 10^{-5}) - \frac{1}{2} log (1)

=9.37 or 9.4

 


Option 1)

2.4

This solution is incorrect

Option 2)

3.6

This solution is incorrect

Option 3)

4.8

This solution is incorrect

Option 4)

9.4

This solution is correct

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