Hello, I just had my first exam yesterday, and I'm always tripped with this question that combines neutralization with buffer solution. The task is to find the pH. I did try to understand the general concept behind it. From my understanding, if CH3COOH reacts with NAOH and the acid has a higher amount of substance (0,005 mol vs 0,004 mol), it means that 0,005 mol of acid is used to neutralize 0,004 mol NAOH, and 0,001 mol of CH3COOH will remain together with 0,004 CH3COONA. To find the pH, one has to use the Henderson-Hasselbach equation and divide the amount of substance with the volume, with pH=pKa-(log c(CH3COOH)/c(CH3COONA). And then if NAOH has a higher amount of substance (0,0051 mol vs 0,005 mol acid), it would create 0,0001 NAOH and 0,005 CH3COONa. So to find the pH, you need to find the pOH of NAOH first. So far so good. But in the solution to the problems posted, there's suddenly an acid popping up in the solution and you have to use Henderson/Hasselbach equation. For example NH3 reacts with HCL and creates NH4CL, even if you have a bigger amount of substance for NH3, you still get an acid on the result... I'm so confused. And then there's an example with the coefficient (NA2CO3 + 2HCL --> 2NACL + H2CO3). if NA2CO3 has a higher amount of substance (let's say 0,224 mol) and HCL only 0,0816 mol, does it mean that it would result in 0,224 mol x 2 - 0,0816 NACL and 0,0816 mol H2CO3? I feel so stupid now that I can't understand this simple concept and keep making mistakes (and wasted like 8 points during the exam).