Salt

Solubility of salt

Preparation of Insoluble salt.

Silver Chloride

Lead(II) Iodide

Outline 1.Definition2.Preparation of

Insoluble Salts3.Example of Insoluble

Salts

Definition

• Solubility of a salt is usually tested by dissolving a little bit of the salt in distilled water.

• Salts that cannot dissolve in water at the room temperature (27oC) are called insoluble salts.

Preparation of Insoluble SaltsInsoluble salts can be prepared through precipitation method or double decomposition reactions.

Precipitation method / Double Decomposition reactions

Two aquoues solutions/soluble salts were mix together

One of the solutions contains the cations of the insoluble salt.

One of the solutions contains the anions of the insoluble salt.

The ions of the two aqueous solutions above interchange to produce two new compound which is insoluble salt or precipitate, and aqueous solution.

The precipitate produced is obtained by filtration. The residue left in the filter paper is the insoluble salt. The filtrate is soluble salt.

 

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The residue/precipitate (insoluble salt) then rinsed with distilled water to remove any other ions as impurities.

Anion(Non-metal ion)

Cation(Metal ion) nn mm

Chemical : MX(aq) + NY(aq) → MY(s) + NX(aq)

equation solution solution precipitate solution

Ionic : M+(aq) + Y-(aq) → MY(s) equation

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Ionic precipitation of Lead(II) Chloride

Na+ Na+

NO3-NO3

-

PbCl2

Pb2+ ions combined with Cl- ions to form white precipitate

Na+ ions and NO3- ions do

not take part in the reaction and are free to move in the solution

Ionic equation : Pb2+ + 2Cl- PbCl2

Pb(NO3)2 solution

(supplies the cation)

NaCl solution(supplies the anion)

Glass rod

PbCl2 salt

(the residue/precipitate)

NaNO3 solution

Mixture of solutionsPb(NO3)2 + NaCl

Filter funnel

Filter paper

Retort stand

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Glass rodDistilled water

Precipitate of lead(II) chloride

Retort stand

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In the formation of the precipitate of lead(II) chloride, PbCl2, the chemical equation can be written:  Pb(NO3)2 (aq) + NaCl (aq) PbCl2(s) + NaNO3 (aq)

  Pb2+ + NO3- + Na+ + Cl - PbCl2 + Na+ + NO3-

 

Ionic equation : Pb2+ (aq) + Cl - (aq) PbCl2 (s)

 

Chemical and ionic equations……continuecontinue

Example of the Insoluble SaltsInsoluble Salt Ions Ionic equation

ZnCO3 Zn2+ , CO32- Zn2+ + CO3

2- ZnCO3

AgCl Ag+ , Cl- Ag+ + Cl- AgCl

BaSO4 Ba2+ , SO42- Ba2+ + SO4

2 BaSO4

PbCl2 Pb2+ , Cl- Pb2+ + Cl- PbCl2

PbSO4 Pb2+ , SO42- Pb2+ + SO4

2- PbSO4

CaCO3 Ca2+ , CO32- Ca2+ + CO3

2- CaCO3

Exercise Refer to handout Exercise 1.

Complete the mind map

handout.