# Degree of dissociation accurately defined

1. Apr 13, 2014

### Entanglement

Is the degree of dissociation the value of

Alpha when the dissociation begins with 1 mole of the solute, or is it alpha when the solute is 1 mole at equilibrium,

There isn't a difference since I'm talking about very weak electrolytes but I want to know the accurate answer.

2. Apr 14, 2014

### Staff: Mentor

Degree of dissociation is a fraction of substance that dissociated, and it doesn't depend on the amount of substance dissolved.

3. Apr 14, 2014

### Entanglement

It's said on Wikipedia that is the value of dissociated moles per 1 mole,

It is meant one mole at equilibrium or when the dissociation begins with that 1 moles ?

4. Apr 14, 2014

### Staff: Mentor

I don't care about what wikipedia says. Degree of dissociation is a fraction of the substance that dissociated. You start with n moles, m moles dissociate, degree of dissociation is m/n.

5. Apr 14, 2014

### Entanglement

Ok, m/n will give the value of m when n is 1, there's no contradiction

6. Apr 14, 2014

### Staff: Mentor

No contradiction, but a lousy thinking. Ratio doesn't require referring to the amount of substance.

7. Apr 14, 2014

### Entanglement

"n moles" is the number of moles at equilibrium or the number of moles that the dissociation starts with ???

8. Apr 15, 2014

### DrDu

The degree of dissociation can be defined independently of equilibrium.
E.g., you could measure it as a function of time after bringing an undissociated substance into a solvent.

9. Apr 15, 2014

### Staff: Mentor

Perhaps it is time you start paying attention to what you read.

10. Apr 15, 2014

### Entanglement

I'm sorry, thanks a lot for you help

11. Apr 15, 2014

### Entanglement

I have a question about the ionic product of water

How is Kw = [ H ] [ OH ] = 10^-14 mole/ liter derived.

12. Apr 15, 2014

### Staff: Mentor

It is not derived, it is determined experimentally.