This document is a chemistry assignment about applying the common ion effect to separate ionic compounds. It discusses how the common ion effect decreases the solubility of an ionic precipitate by adding a soluble compound that shares an ion with the precipitate. As an example, it explains that the solubility of calcium fluoride decreases if additional calcium ions are added from another source, since both share the calcium ion. The student then proposes using the common ion effect to separate lithium hydroxide by adding carbonate ions, which will form less soluble lithium carbonate precipitate.

1. CHEMISTRY ASSINGMENT
TOPIC:
“Application of common ion effect for the separation
of ionic compounds”
STUDENT NAME:
Sadaf Batool
DEPARTMENT
CHEMISTRY
REG NO:
BSCSR07193013
THE UNIVERISTY OF LAHORE

2. Common ion effect:
The common-ioneffectreferstothe decrease insolubilityof anionicprecipitate bythe additiontothe
solutionof asoluble compoundwithanionincommonwiththe precipitate.[1] Thisbehaviourisa
consequence of Le Chatelier’sprinciple forthe equilibriumreactionof the ionicassociation/dissociation.The
effectiscommonlyseenasaneffectonthe solubilityof saltsandotherweakelectrolytes.Addingan
additional amountof one of the ionsof the salt generallyleadstoincreasedprecipitationof the salt,which
reducesthe concentrationof bothionsof the salt until the solubilityequilibriumisreached.The effectis
basedon the fact that boththe original saltandthe otheraddedchemical have one ionincommonwith
each other.
Separation on the basis of common ion effect:
Wheneverasolutionof anionicsubstance comesintocontactwithanotherioniccompoundwithacommon
ion,the solubilityof the ionicsubstance decreasessignificantly.Forexample,thiswouldbe liketryingto
dissolve solidtable salt(NaCl) inasolutionwhere the chloride ion(Cl–) isalreadypresent.The amountof
NaCl that coulddissolve toreachthe saturationpointwouldbe lowered.Thisphenomenonisthe common
ioneffectandplaysimportantrolesinpharmaceutical andenvironmental areas.The commonioneffectcan
be explainedbyLe Chatelier’sprinciple of chemical equilibrium:
[latex]AB_{(s)}leftrightarrow{ A^+ }_{ (aq) } + { B^-}_{ (aq) }[/latex]
For a simple dissolutionprocess,the additionof more of one of the ions(A+) fromanothercompoundwill
shiftthe compositiontothe left,reducingthe concentrationof the otherion(B–),effectivelyreducingthe
solubilityof the solid(AB).Forexample,whencalciumfluoride dissolvesintocalciumandfluoride ions,the
solubilityproductexpressionis:
[latex]CaF_{2(s) }leftrightarrow{ Ca^{+2} }_{ (aq) }+{ 2F^{-} }_{ (aq) }[/latex]

3. Thisexpressionmustalwayshold,evenif some ionicspeciescome fromothersources.Therefore,if more
[latex]Ca^{+2}[/latex] ionsare placedinsolution,the equilibriumwill shifttothe left,favoringthe solidform
and decreasingthe solubilityof the solid.
Lithiumhydroxidewithcarbonate growthsLithiumhydroxide formsless-soluble lithiumcarbonate,which
precipitates becauseof the commonioneffect.
THANK YOU.