Question

Calculate the solubility of AgCl in a solution containing 0.1M MgCl2 and 0.2M AgNO3

I dont understand why here the reaction moves to reactant

When doing the ICE table, the "C" is -x for Ag+ and Cl-

Answer 1

AgCl-> Ag+ + Cl-
Now There is already Ag+ and Cl- in the medium as MgCl2 and AgNo3 are strong electrolytes.
Suppose new solubility of AgCl is s
AgCl-> Ag+ + Cl-
s+0.2 s+0.2
Ag+ is now s+0.2(0.2 comes from AgNo3)
now solve it as (s+0.2)^2=Ksp

Answer 2

Reaction moves to rectants side according to Le Chateliers principle.

Answer 3

so do you determine if it moves to reactant side or product side by the Ksp value?
I've learnt that Ksp < 0 : moves to reactant
Ksp > 0 : moves to product

Answer 4

No You are talking about ionic product Ksp is a constant irrespective of the conditions,Anyway if you solve s^2 + Ksp
and then find solubility in pure water,you'll find s will be more for pure water than here in this solution. Ksp never changes.

Answer 5

Ksp is always a positive constant.

Answer 6

but this question given that Ksp AgCl = 1.8 x 10^-10
so it is not related on the reaction shifting reactant or to products?

Answer 7

Ksp has nothing to do with it ,it is the solubility s that you should find.
Let us take AgCl pure water
AgCl-> Ag+ + Cl-
s s
s^2=1.8*10^-10= approx 1.4*10^-5
now lets take AgCl in the given solution.
AgCl-> Ag+ + Cl-
s+0.2 s+0.2
(s+0.2)^2=1.8*10^-10. Now if you calculate s you get a negative quantity, That basically means the solution is beyond saturated and AgCl starts to precipiate, If AgCl starts to precipitate then reaction is obviously moving to reactants side.
I think what you are trying to ask is about ionic product....

Answer 8

Ionic product= (Ag+)* (Cl-)
In any sparingly soluble salt if ionic product is greater than Ksp it means that reaction will proceed in backward direction with AgCl precipiating until the concentration of Ag+ and Cl- has been reduced till ionic product is equal to Ksp.
If ionic priduct is less than Ksp then the reaction will proceed forward with more AgCl disocciating to give Ag+ and Cl- Till again the ionic product becomes equal to Ksp.

Answer 9

i didnt learn about the pure water stuff yet :(
and yea, i think i'm talking about the ionic product too
my teacher didnt talk much about it

we need to find Q and compare it with Ksp
if Q is greater than K, then precipitate forms

Answer 10

Correct.

Answer 11

but then since i didnt learn about the pure water stuff, so i cant use ur way to determine if ppt forms or not

if i do 1.8 x 10^-10 = (0.2 -x)^2
x = 0.1999

and 1.8x 10 ^-10 = (0.2+x)^2
x= - 0.1999

is there another way to detminer if ppt forms other then compare it to water?

Answer 12

and thanks for ur help!

Answer 13

Well the ionic product method is a better method just find the concentrations of the products and multiply them and compare it to Ksp, Finding s is an uneccessary step, I just told you that since you wanted solubility.

Answer 14

ohhhh i get it now! so 0.2 x 0.2 = 0.04 and is larger than Ksp, that means precipitate forms!!

oh thanks thanks thanks!

Answer 15

Great work. Thanks Shanvee for your explanation and thanks LovekBlue for seeking to understand!