What is the ph of a solution containing 0.12 mol/l of nh4cl and 0.03 mol/l of naoh (pka of is 9.25)?

(NH4)+ from NH4Cl will react with (OH)- to form NH3 and H2O

So, 

concentration of NH4+ = 0.12
and concentration of OH- = 0.03

Concentration of Remaining (NH4)+ = 0.12 - 0.03 = 0.09 mol /L 
Concentration of Generated NH3 = 0.03 mol / L 

The resulting solution is " NH4+ / NH3 Buffer System " { (NH4)+ is acid ; NH3 is Base ( " Salt " ) } 

For a Buffer System, the formula for pH is :





= 9.25 + Log 3 
= 9.25 + 0.4771 
= 9.73 (after rounding off)

Thermohaline circulation and gyres