6.4 solubility equilibria

Question 1

define solubility

Answer 1

the maximum mass or amount of solute that can be dissolved per dm3 of solvent to produce a saturated solution at a given temperature

Question 2

define solubility product

Answer 2

an equilibrium constant which is the product of molar concentrations of the dissolved ions in a saturated solution of the salt at a given temperature

Question 3

what are the factors affecting solubility of salt?

Answer 3

1. common ion effect
2. formation of complexes
3. pH of solution

Question 4

explain how common ion effect decreases solubility of an ion

Answer 4

the NaX solution contains the common ion, X-. by Le Chatelier’s principle, the presence of greater [X-] causes equilibrium to shift to the left to decrease the concentration of common ion X-. this suppresses the dissociation of MX and reduces its solubility.

Question 5

explain how pH (adding acid) will affect solubility

Answer 5

addition of H+ from acid will neutralise OH-, hence [OH-] decreases. by Le Chatelier’s principle, position of equilibrium shifts to the right to increase [OH-], increasing solubility

Question 6

define ionic product

Answer 6

the product of molar concentrations of the constituent ions in the solution at that instant raised to appropriate powers at a given temperature

Question 7

how does comparing ip and Ksp show whether precipitation has occured?

Answer 7

ip > Ksp, ppt observed
ip = Ksp, trace ppt
ip < Ksp, no ppt

because Ksp is at saturation point, ip compares concentrations with saturation point