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Ionic product of water and bases Watch

1. I'm so confused with this concept. If there's a base that's been dissolved in water then it would release OH- ions so the concentration of OH- ions will be greater than the concentration of H+ ions, but together they will still equal the ionic product of water. But how does this work exactly? How is it that the exact right concentration of H+ is present so that the OH- and H+ equal to 1.00 x 10-14 mol2 dm-6? And most importantly where do these H+ ions come from?
2. (Original post by tazmaniac97)
I'm so confused with this concept. If there's a base that's been dissolved in water then it would release OH- ions so the concentration of OH- ions will be greater than the concentration of H+ ions, but together they will still equal the ionic product of water. But how does this work exactly? How is it that the exact right concentration of H+ is present so that the OH- and H+ equal to 1.00 x 10-14 mol2 dm-6? And most importantly where do these H+ ions come from?
H2O <==> H+ + OH-

The ions come from the dissociation of water. If the hydroxide ion increases then the equilibrium moves to the left hand side removing hydrogen ions until the value of kw is reasserted...
3. (Original post by tazmaniac97)
I'm so confused with this concept. If there's a base that's been dissolved in water then it would release OH- ions so the concentration of OH- ions will be greater than the concentration of H+ ions, but together they will still equal the ionic product of water. But how does this work exactly? How is it that the exact right concentration of H+ is present so that the OH- and H+ equal to 1.00 x 10-14 mol2 dm-6? And most importantly where do these H+ ions come from?
Water molecules can function as both acids and bases. One water molecule (acting as a base) can accept a hydrogen ion from a second one (acting as an acid). This will be happening anywhere there is even a trace of water - it doesn't have to be pure.

A hydroxonium ion, H3O+ (Not H+), and a hydroxide ion are formed.

However, the hydroxonium ion is a very strong acid, and the hydroxide ion is a very strong base. As fast as they are formed, they react to produce water again.
The net effect is that an equilibrium is set up.

Kw is essentially just an equilibrium constant for the reactions shown. You may meet it in two forms:

Based on the fully written equilibrium . . .

. . . or on the simplified equilibrium:

Like any other equilibrium constant, the value of Kw varies with temperature. Its value is usually taken to be 1.00 x 10-14 mol2dm-6 at room temperature.
4. (Original post by charco)
H2O <==> H+ + OH-

The ions come from the dissociation of water. If the hydroxide ion increases then the equilibrium moves to the left hand side removing hydrogen ions until the value of kw is reasserted...

(Original post by yarshad)
Water molecules can function as both acids and bases. One water molecule (acting as a base) can accept a hydrogen ion from a second one (acting as an acid). This will be happening anywhere there is even a trace of water - it doesn't have to be pure.

A hydroxonium ion, H3O+ (Not H+), and a hydroxide ion are formed.

However, the hydroxonium ion is a very strong acid, and the hydroxide ion is a very strong base. As fast as they are formed, they react to produce water again.
The net effect is that an equilibrium is set up.

Kw is essentially just an equilibrium constant for the reactions shown. You may meet it in two forms:

Based on the fully written equilibrium . . .

. . . or on the simplified equilibrium:

Like any other equilibrium constant, the value of Kw varies with temperature. Its value is usually taken to be 1.00 x 10-14 mol2dm-6 at room temperature.
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Updated: April 5, 2013
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