1) In Lab 3, Solubility Rules, students identified ionic salts as soluble or ins

Question

1) In Lab 3, Solubility Rules, students identified ionic salts as soluble or insoluble. The solubility of ionic salts is quantified by an equilibrium constant called Ksp, the solubility product. This Ksp refers to the dissolution reaction of the ionic salts. (a) Write the dissolution reaction for the ionic solids below. (Use the lowest possible coefficients. Include states-of-matter under the given conditions in your answer.)
(i)    KBr

(ii)   KClO4

(iii)    AlPO4

2) The concentration of cations and anions in solution can be predicted from the equation

[cation] =

for ionic solids in which the ratio of cation to anion is 1:1. Calculate the [cation] concentration of a saturated solution containing the salts below. Indicate if the reaction prefers reactant or product at equilibrium.

reactant or product    

reactant or product    

reactant or product    

(c) There is a general relationship between the charges on ions and the Ksp value. Complete the sentence below to describe this relationship.

The (smaller or larger) the Ksp value, the more product that is formed at equilibrium.

The lower the charges on the ions in an ionic solid, the more (soluable or unsoluable) the solid is.

Explanation / Answer

(i)    KBr(s) ----> K+(aq) + Br-(aq)

(ii)   KClO4 ---> K+(aq) + ClO4(aq)

(iii)    AlPO4 --> Al+3(aq) + PO4-3(aq)

b)

Since Ksp = [Cation][Anion] then

If Solubility = S then

Ksp = S*S ---> S^2 = Ksp --> S = sqrt(Ksp)

(i)    KBr(s) ----> K+(aq) + Br-(aq) Ksp = 3.25101 --> S = sqrt(3.25*10^1) = 5.7 M

(ii)   KClO4 ---> K+(aq) + ClO4(aq) Ksp = 1.05102 --> S = sqrt(1.05*10^-2) = 0.102 M

(iii)    AlPO4 --> Al+3(aq) + PO4-3(aq) Ksp = 9.841021 --> S = sqrt(9.84*10^-21) = 9.9*10^-11 M

C)

The (smaller or larger) the Ksp value, the more product that is formed at equilibrium.

If Ksp is too low, this means there is no cation/anion in solution favoured, therefore expect solid (precipitate)

The lower the charges on the ions in an ionic solid, the more (soluable or unsoluable) the solid is.

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