Now Aqueous solutions, unlike pure water, solutions resist changes in PH when we add acid or base. And that's because aqueous solutions have buffer systems. And a buffer is simply a chemical system which resists a PH change. So for example, suppose we had a system of 0.5 molar of acetic acid mixed with 0.5
molar of sodium acetate in one liter of water, and this PH and this system's PH was 4.74. So now what happens to our PH if we add 0.1 molar of hydrochloric acid, as we did in part A? Well, now our PH will only decrease from 4.74
to 4.72.