Which of the following solutions is the most basic? (a) 0.6 M NH 3, (b) 0.150 M KOH, (c) 0.100 M Ba(OH)2. Explain.
So in this question we're asked, which of the following compounds is most basic. And what we need to realise here is that a common definition of basicity, has to do with the concentration of hydroxide ion. So most basic would mean the one that possesses the greatest concentration of hydroxide ions. Those little brackets there mean concentration. Another name for concentration is molarity.
So the compounds that we're looking at here, we have our 0.6 molar NH3 0.150 molar KOH, and 0.100 molar barium hydroxide. Now, first of all, we're going to say that NH3 is ammonia, ammonia is a weak base. It's a weak base meaning it produces very litte hydroxide ion. And the way it forms hydroxide ion is that it reacts with water, water actually gives away a hydrogen to it, and there goes the hydroxide ion that is formed, but you don't have to go through all of this you will learn all about this later on when we take a deeper look into acids and bases and their reaction, but realise NH3 is a weak base, weak bases don't produce much hydroxide ion. KOH is a strong base, which means it breaks completely into it's ions. So we will get K+ ion plus OH- ion, since it breaks up 100% that means that the concentration of the compound is equal to the concentration of the ions. So we have the concentration of the hydroxide ion here as 0.150 molar. Barium hydroxide is also a strong base so it also breaks up into ions completely, but now we have two hydroxide ions here. Here's the thing, there's one barium, so it's concentration is the same as the concentration of the compound, but hydroxide has a two in front of it, so that means we multiply the concentration here times two, because there's two hydroxide ions. So here the concentration of hydroxide ions would be 0.200 molar, so as a result, the compound that has the greatest concentration of hydroxide ions is the barium hydroxide, therefore will be the most basic.
Remember basicity deals with the concentration of OH-, and acidity deals with the concentration of H+ ion. Here it doesn't talk about that, but just incase you see a question like that, it's talking about which has the highest concentration of H+ ions.