That's a very big increase in PH. So the takeaway from this is that adding a small amount of acid or base to pure water will drastically change the PH of water. Now, if you're confused about how we got this part or this part, check out the link below. 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.