Question

152. A water having PH = 9, will have hydroxyl
ion concentration, equal to:
1. 109
3. 10-9 4. 105
2410-5​

Answer 1

For now we will stick with the Brønsted-Lowry definition. And we will now tie the concept of acids and bases into equilibrium:

Let's start by looking at the Ionization of Water:

2H2O(l) <=> H3O+(aq) + OH-(aq)

 

This reaction does fit the Brønsted-Lowry definition since one water molecule is acting as an acid "donating" a proton and the other is acting as a base "accepting" the proton:

Bronsted Water

If we now write this reaction into an equilibrium expression:

Kw

 

But remember one of our rules regarding the writing of equilibrium expressions states that we do not include solvents (liquids) as their concentration stays pretty constant during a reaction so the water portion of the equation is essentially equal to 1 and thus "disappears".

The resulting equation is given a special designation KW called the ionization constant of water: Kw