Solubility

Unit 7

Sparingly Soluble Salts

salts (ionic compounds) that are insoluble in water

why are ionic compounds insoluble in water

the crystal lattice structure is too strong and water cannot enter, ionic bonds are too strong and water molecule cannot substitute for ionic bond

molar solubility

concentration of a salt in 1L of water

1:1 salts

ex: AgCl

x=√ksp

1:2 salts

ex: Ag2CrO4

x=3√ksp/4

1:3 salts

ex: Ag3PO4

x=4√ksp/27

how to compare if ksp will form

calculate Q and compare it with ksp

Q>ksp

precipitate will form

Q

precipitate will not form

Q=ksp

solution is just saturated

Will precipitate form when 1L of 3x10^-10M Co(NO3)2 is added to 1L of 2x10^-11 K2S (ksp CoS = 5x10^-22)

1. calculate Q and compare with ksp
2. final volume is 2L since dilution has already occured
3. use c1v1=c2v2 to find new \[Co\] and \[S\]

if ksp is small…

many reactants are present

when can we ignore +x

when ksp is very small, it means that +x is also very small and won’t change the concentration much, so 0.1 +x becomes 0.1

why is there a reduction in solubility with NaCl compared to solubility in water

the Cl ions already in solution from NaCl have taken up room so not many Cl ions from AgCl can enter solution

common ion effect

the reduction of solubility