Explanation:
It is known that  of
 of  =
 =  .
.
(a)  Relation between  and
 and  is as follows.
 is as follows.
                        
Putting the values into the above formula as follows.
                       
                                     = 
                                      = 3.347
Also, relation between pH and   is as follows.
 is as follows.
               pH = ![pK_{a} + log\frac{[conjugate base]}{[acid]}](https://tex.z-dn.net/?f=pK_%7Ba%7D%20%2B%20log%5Cfrac%7B%5Bconjugate%20base%5D%7D%7B%5Bacid%5D%7D)
                      = 
                     = 3.44
Therefore, pH of the buffer is 3.44.
(b)   No. of moles of HCl added = 
                                             =  
 
                                              = 0.0116 mol
In the given reaction,  will react with
 will react with  to form
 to form 
Hence, before the reaction:
No. of moles of  =
 = 
                                            = 0.15 mol
And, no. of moles of  =
 = 
                                                = 0.12 mol
On the other hand, after the reaction :  
No. of moles of  = moles present initially - moles added
 = moles present initially - moles added
                                           = (0.15 - 0.0116) mol
                                           = 0.1384 mol
Moles of  = moles present initially + moles added
 = moles present initially + moles added
                                = (0.12 + 0.0116) mol
                                 = 0.1316 mol
As,  =
 = 
            
                          = 
                          = 3.347
Since, volume is both in numerator and denominator, we can use mol instead of concentration.
As, pH = ![pK_{a} + log \frac{[conjugate base]}{[acid]}](https://tex.z-dn.net/?f=pK_%7Ba%7D%20%2B%20log%20%5Cfrac%7B%5Bconjugate%20base%5D%7D%7B%5Bacid%5D%7D)
             = 3.347+ log {0.1384/0.1316}
             = 3.369
             = 3.37 (approx)
Thus, we can conclude that pH after the addition of 1.00 mL of 11.6 M HCl to 1.00 L of the buffer solution is 3.37.