How do you know when you're doing a chem eqn whether to write
a) HA -> H+ + A-
or
b) A- + H2O -> HA + OH-
because i read it had somewhere to do with acids or bases or the strength of the acid......and i just got *reallly* confused.
Thanks.
From my somewhat limited knowledge of this topic, it looks like the first reaction you have is an acid ionising in water, and the second is the conjugate base of the acid reacting with water to produce the A- ion?
It should have to do with acids and bases- the acids will ionise in water to produce the hydronium ion, eg HCl ionising in water:
HCl + H2O -->
H3O+ + Cl-
And bases will react to form a conjugate acid, and an OH- ion. I think. Eg, K2SO4 is a basic salt as
K2SO4 (s) <---> 2K+ (aq) + SO4 2- (aq)
SO4 2- (aq) + H2O (l) <---> HSO4 - (aq) +
OH- (aq).
The strength of the acid/base just determines whether the reaction is complete or at equilibrium, ie whether the arrow is one way or not. Strong acids/bases ionise completely, so the it goes to the right.
I think that's it, can someone who's done this topic check for me? Hope that helps :]