What does molarity mean in case of weak electrolytes?

[AnkurGarg]

I am really confused about it.Suppose we add 5 moles of acetic acid in 1 litre of water..The molarity of solution will be -(5 moles)/volume of solution?Or it will be -(the number of moles of acetic acid dissociated/dissolved)/volume of solution

 

[crador]

I believe molarity is defined as the number of moles dissolved or otherwise well mixed into solution. Vinegar and water are quite miscible so far I know, so it would be 5 moles/ liter.

 

[Borek]

Molarity of what?

Formal concentration (also called analytical concentration) of acetic acid - 5 M.

Equilibrium concentrations of HAcetate, Acetate^-, H⁺ will be different, you can estimate them to be approximately 4.990 M, 9.34×10^-3 M and 9.34×10^-3 M respectively. One thing you can be sure about is that [HAcetate] + [Acetate^-] = 5 M (this is mass balance of acetic acid).

 

[DrDu]

No, molarity always is the quotient of moles per total volume, so 5 moles of acetic acid and one liter of water give a molarity less than 5 moles/l.

 

[Borek]

Good point.

Assuming 1 L of water and 5 moles of acetic acid final solution would be 3.96 M.