[ygao85]

I am a little confused about the Ksp. If we take Ag₂S for example, is the Ksp:

[2Ag]² or [Ag]²?

Thank you

[AWK]

Square brackets [ ] mean molar concentration at the equilibrium.
Hence the second form is correct. But for calculations you should put number and you can see from stoichiometry of Ag2S dissociation in water that the equlibrium concentration of Ag+ cation is doubled as compared to concentration of S2- anion.

[Donaldson Tan]

[2Ag]² or [Ag]²?

neither.

Ag₂S <-> 2Ag⁺ + S^2-

Ksp = [[ Ag⁺ ]]² [[ S^2- ]]