Common ion effect (1 Viewer)

[weezby]

Originally posted by Giant Lobster
I dont get it
why don't solids affect equilibria?
consider saturated NaCl
so NaCl(s) <=> Na + Cl
but NaCl(s) does not participate in teh equilibrium, so the LHS is empty hmmm I guess its possible, but it just doesnt seem right in a chem reaction to have one whole side as void.

umm..

For slightly soluble salts, we have the equilibrium of a solid salt with its ions in solution. Since the concentration of a pure substance in the solid (or liquid) phase remains constant, the equilibrium constant expression may be simplified to a form called the solubility product law. The solubility product law states that in a saturated solution of a slightly soluble salt, the product of molar concentrations of its ions in its saturated solution is a constant, the solubility product constant or K_sp.

AB(s) <=> A+ (aq) + B- (aq)
Ksp = [A+][B- ]

For NaCl, its K_sp is very large..
i.e. most of the NaCl(s) dissociates.. amount of NaCl(s) is negligible..

 

[Giant Lobster]

yep thanks i kinda get it now
i think i may have confused this phenomena with what the 'common ion effect' realy is... hmm
o well, thanks.

hsc is made so that students who know what to write gets the heighest marks... since 75% of the exam is in english written form, rather than more mathematical&chemical form, and multiple-choice type of question which directly tests understanding instead of being able to explain properly with proper grammar in strict time conditions... to me anyway since i write slow, and cannot think and write at the same time. but even worse is that they bring in stuff from social sciences like evaulate and assess in terms of cost, evironment and etc.

yeah i know what u mean. Grammar is actually a criteria that is assessed in physics and chemistry in our school
lamers cant think of something else to put there to make the total mark a round factor of 10.

 

[weezby]

Originally posted by Giant Lobster
yep thanks i kinda get it now
i think i may have confused this phenomena with what the 'common ion effect' realy is... hmm
o well, thanks.

a more appropriate example of common-ion effect..

http://dbhs.wvusd.k12.ca.us/Equilibrium/Common-ion-effect.html

common-ion effect is basically the effect seen when u mix an ion common to a slightly soluble salt equilibria ---> affects the position of the equilibirum of the slightly soluble salt system

sorry, i just realised i've reiterated what has been said before..