Question

What is the $ pH $ of a $ 0.150M $ solution of sodium acetate ( $ NaO_2CCH_3 $)? $ Ka(CH_3CO_2H) = 1.8 \times 10^ { -5 }.$

Answer 1

Hint: For solving the given problem, we should have knowledge about salt hydrolysis, $ pH $, acidic constant $ Ka $ and calculation of $ log $.
Salt hydrolysis is a process where the reactants are salt and water forming an acidic or basic solution. $ pH $ is described as power of hydrogen or potential of hydrogen. It is used to describe the concentration of hydrogen and is inversely proportional to it.
Acidic constant or Acid Dissociation constant, $ Ka $ is used to quantitatively measure the acidic strength in a solution.
$ pH $ for basic solution;
$ pH = 7+\dfrac{ 1 }{ 2 } [P_{ Ka } + logC ] $
Where, C is concentration of salt.
$ P_{ Ka } $ can be calculated as ;
$ P_{ Ka } = -log Ka $.

Complete step by step solution:
Step-1 :
First we have to determine that the given salt is if hydrolysed contains what products. On hydrolysis of Sodium acetate, $ NaO_2CCH_3 $, we get a strong base $ NaOH $ and a weak acid $(CH_3CO_2H) $ (acetic acid).
Step-2 :
The formula for $ pH $ of salt of strong base and weak acid is :
$ pH = 7+\dfrac{ 1 }{ 2 } [P_{ Ka } + logC ] $
Since, the $ pH $ is basic.
Step-3 :
Here, we have given $ Ka = 1.8 \times 10^{ -5 } $ and $ C = 0.15M $.
For, $ P_{ Ka } = -log Ka $
$ =-log(1.8 \times 10^{ -5 } $
$ =4.76 $
Putting the above values in formula, we get;
$ pH = 7+\dfrac{ 1 }{ 2 } [4.76 + 0.15 ] $
$ =9.455 $

Note:
While calculating the $ pH $, make sure that salt hydrolysis is correct and the $ pH $ is according to that acidic or basic solution, for basic solution, $ pH $ is added and for acidic solution, $ pH $ is subtracted.