CHAPTER 8: SALTS

W H O I S S A L T ?

W H O I S S A LT ?WHAT IS SALT ?

Ionic compound – formed when the hydrogen ion, H+ from an acid is replaced by a metal ion or an ammonium ion, NH4

+

REFER TEXT BOOK : PAGE 138

EXAMPLE :

Na+

NH4+

H ClMetal ions

Ammonium ion

Na+ Cl-

NH4+ Cl-

replace

replace

Ammonium chloride

Sodium chloride

SALTS CONSIST ANION PART COMES FROM THE ACID WHILE CATION PART COMES FROM BASES

Common cations

Common anions

(parent acids)

HCl

HNO3

H2CO3

H2SO4

Na+

K+

NH4+

Ca2+ Mg2+

Cu2+

Fe2+

Fe3+

Al3+ Zn2+

Pb2+

Metal ion

Sulphate salts

+ H2SO4

Chloride salts+ HCl

Carbonate salts

+ H2CO3

Nitrate salts

+ H2NO3

Na + Na2SO4 NaCl Na2CO3 NaNO3

Mg 2+ MgSO4 MgCl2 MgCO3 Mg(NO3)2

Cu 2+ CuSO4 CuCl2 CuCO3 Cu(NO3)2

Al 3+ Al2(SO4)3 AlCl3 Al2(CO3)3 Al(NO3)3

METAL ION DISPLACE H+ ION IN ACIDS

All nitrate salts ; soluble saltsBarium nitrate,

Ba(NO3)2

Calcium nitrate,

Ca(NO3)2

Aluminium nitrate,

Al(NO3)3

Silver nitrate, AgNO3

Lead(II) nitrate,

Pb(NO3)2

Potassium nitrate, KNO3

Sodium nitrate,NaNO3

Copper(II) nitrate,

Cu(NO3)2

Iron(III) nitrate,

Fe(NO3)3

SOLUBLE SALT

NO3-

ALL

All Na+, K+, NH4+ salts ; soluble salts

Potassium carbonate,

K2CO3

Sodium carbonate,

Na2CO3

Ammonium carbonate, (NH4)2CO3

Potassium sulphate,

K2SO4

Potassium chloride,

KCl

Potassium nitrate, KNO3

Sodium nitrate,NaNO3

Sodium chloride,

NaCl

Ammonium sulphate, (NH4)2SO4

SOLUBLE SALT

ALLNa+, K+, NH4

+

All carbonate salts ; insoluble saltsMagnesium carbonate

MgCO3

Calcium carbonate

CaCO3

Silver carbonate

Ag2CO3

Other names[hide]Silver(I)Carbonate

Copper(II) carbonate

CuCO3

Zinc carbonate

ZnCO3

Manganese(II) carbonateMnCO3

EXCEPTPotassium carbonate

K2CO3

SodiumCarbonate

Na2CO3

Ammonium carbonate

(NH4)2CO3ALL

Na+, K+, NH4+

CO32-

INSOLUBLE SALT

EXCEPT

Mercury(II) Chloride

HgCl2

All SO42-, Cl- salts ; soluble salts

EXCEPT EXCEPTSilver(I) Chloride

AgCl

Lead(II) Chloride

PbCl2

SOLUBLE SALT

Cl-ALL

Barium sulphate

BaSO4

Lead(II) sulphate

PbSO4

Calcium(II) sulphate

CaSO4

SOLUBLE SALT

SO42-

ALLPb2

+

Ag+ Hg2

+

Pb2+

Ca 2+

Ba2+

EXCEPT

Copper(II) ChlorideCuCl2

Iron(II) ChlorideFeCl2

MagnesiumChlorideMgCl2

Copper(II) sulphateCuSO4

Aluminium(II) sulphate

Al2(SO4)3

ZincChlorideZnCl2

Potassium chloride,

KCl

Sodium chloride,

NaCl

INSOLUBLE SALT

SOLUBLE SALT

NO3-ALL ALL

CLASSIFICATION OF SALTS

PbSO4

CaSO4

BaSO4

PbCl2

AgCl

ALLCO3

2-

SO42-

Cl-

ALL

Na+, K+, NH4+

ALL

OTHER SOLUBLE SALTS

PREPARATION OF SALTS

SOLUBLE SALTS INSOLUBLE SALTS

ACID + ALKALI

NEUTRALISATION

[SPA]Sodium ,Na+ saltsPotassium, K+ salts

Ammonium, NH4+ salts

OTHER METHODACID + METAL

ACID + METAL OXIDE

ACID + METAL CARBONATE

PRECIPITATION

INSOLUBLE SALT & SOLUBLE SALT

SOLUBLE SALT +SOLUBLE SALT

PREPARATION OF SOLUBLE SALTS[ SODIUM SALTS / POTASSIUM SALTS / AMMONIUM SALTS ]

NEUTRALISATION REACTION

PREPARATION OF POTASSIUM CHLORIDEEXAMPLE

K OHALKALI

H ClACID

ClK H2OSALTS

TITRATION METHOD – FIND OUT THE EXACTLY VOLUME OF ACID REQUIRED TO NEUTRALISE ALKALI.END POINT – POINT WHEN INDICATOR CHANGES COLOUR DURING TITRATION

NOTE : CONCENTRATION AND VOLUME OF ALKALI ARE KNOWN.

LET DO THIS: PREPARATION OF POTASSIUM CHLORIDE

APPARATUS : Pipette 25mL, Burette 50mL, Conical Flask 250 mLMATERIALS : Potassium hydroxide 1.0 M, Hydrochloric acid 1.0 M, Phenolphthalein

Use a pipette to transfer 25.0 cm3 of potassium hydroxide solution to a conical flask. Add 2 to 3 drops of phenolphthalein

Colourless KOH turn to pink.

Fill a burette with hydrochloric acid and record the initial burette reading.

Record the burette reading in 2d.p

Slowly adding the acid into the conical flask and swirls- until the indicator turns from pink to colourless. Record the volume of acid used. (V cm3)

Record the final burette reading in 2d.p

Pipette 25.0 cm3 of the same potassium hydroxide solution into a conical flask.Do not add any indicator.

From the burette, add exactly V cm3

of hydrochloric acid to the alkali and swirls and shake well.

PREPARATION OF POTASSIUM CHLORIDESTART OVER AGAIN BUT WITHOUT INDICATOR : To get the pure and neutral salt solution

RECRYSTALLISATION PROCESS[PURIFIED SOLUBLE SALTS]

HEATING/EVAPORATE

COOLING

FILTRATION

DRY

C R Y S TA L S A LT

Solution salt contains impurities continuous with recrystallisation process

PREPARATION OF SOLUBLE SALTS[ OTHER SALTS EXCEPT Na+, K+, NH4

+]

OTHER METHOD : DISSOLVE METAL IN ACID

Pour 50 cm3 of sulphuric acid into a beaker. Warm the acidUse a spatula to add copper(II) oxide powder bit by bit into the acid. Stir the mixture well. Continue adding copper(II) oxide until some of it no longer dissolves(excess unreacted metal

See the change of metal solid colour and dissolve

Solution salt contains impurities continuous with recrystallisation process

Glass rod

Acid

Metal/ metal oxide/ metal carbonate

Excess unreacted metal (residue)

Evaporating basin with salt solution (filtrate)

HEATING/EVAPORATE COOLING

Evaporating basin

Salt solution

RECRYSTALLISATION PROCESS [PURIFIED SOLUBLE SALTS]

FILTRATION

RECRYSTALLISATION PROCESS [PURIFIED SOLUBLE SALTS]

DRY C R Y S TA L S A LT

The crystals are filtered and rinsed with a little cold distilled water.

Rinse with

distilled water

Glass rod

Salt Cystals Filter Paper

These physical characteristics:• Regulars geometry shapes,

such as cubic or hexagonal.• Flat faces, straight edges and

sharp angles.• Same angle between adjacent

faces.

DISSOLVE SOLUTE IN ACID

HEATINGDISSOLVE METAL IN ACID

EXCESS METAL NOT DISSOLVE

COMPLETE REACT

NEUTRALISATION REACTION

1ST TITRATION WITH INDICATOR

FIND VOLUME OF ACID

2ND TITRATION NO INDICATOR

GET PURE SALT

PREPARATION OF SOLUBLE

SALTS

TRANSFER TO EVAPORATING

BASIN

HEATING/EVAPORATE

COOLINGFILTRATION

DRY

RECRYSTALISATION

C R Y S TA L S A LT

PREPARATION OF INSOLUBLE SALTS[ ALL CARBONATE SALTS except Na+/K+/NH4

+ ]PbSO4 / CaSO4/ BaSO4/PbCl2/ AgCl ]

PRECIPITATION REACTIONPREPARATION OF LEAD(II) CHLORIDEEXAMPLE

Na ClSOLUBLE

SALTS

Pb NO3

SOLUBLE SALTS

NO3NaINSOLUBLE

SALTS

DOUBLE DECOMPOSITION METHOD – TWO AQUOUES SOLUTIONS/SOLUBLE SALTS WERE MIX TOGETHER INTERCHANGE TO PRODUCE TWO NEW COMPOUND WHICH IS INSOLUBLE SALT OR PRECIPITATE, AND AQUEOUS SOLUTION/SOLUBLE SALTS

Cl2Pb

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

[one of the solutions

contains the anions of the

insoluble salt]

two aquoues solutions/soluble salts were mix together

[one of the solutions

contains the cations of the

insoluble salt]

PREC

IPIT

ATIO

N R

EAC

TIO

N

Mixture solutions

Filter paper

Retort stand

Precipitate (residue)

Filter funnel

Aqueous Solution (filterate)

Glass rod

Filtration : Remove solution from precipitate

Glass rodDistilled

water

Precipitate (residue)

Rinse : remove other ions from precipitate

PREC

IPIT

ATIO

N R

EAC

TIO

N

FILTRATION RINSE

PREC

IPIT

ATIO

N R

EAC

TIO

N Filter paperPrecipitate/Soluble salts

Dry : Dried by pressing between two pieces of filter paper.

FLOW CHART : PREPARATION OF INSOLUBLE SALTS

MIX - STIRTWO SOLUBLE SALTS

FILTRATIONREMOVE FILTRATE

RINSEREMOVE OTHER IONS

DRYPRESS BETWEEN FILTER PAPER

PREPARATION OF SALTSREMEMBER : METAL ION DISPLACE

HYDROGEN ION IN ACID TO FORMED SALTSHCl [H+/Cl-]

Hydrochloric acidHNO3 [H+/NO3

-]Nitric Acid

H2SO4 [2H+/SO42-]

Nitric AcidH2CO3 [2H+/CO3

2-]Nitric Acid

METAL / AMMONIUM ION

Na+

K+

NH4+

Ca2+

Mg2+ Cu2+

Fe2+Fe3+

Al3+

Zn2+

Pb2+

SUM

MA

RIE

S O

F R

EAC

TIO

N Method/Reaction Reason Type of Salts

(Metal) Neutralisation

(Titration method)Alkali + Acid Salts + Water

Salts of sodium, potassium, and ammonium

ions are soluble.

Na+ K+

NH4+

Metal DisplacementMetal + Acid Salts + Hydrogen

More electropositive metals can displace hydrogen ion

from acid.

Ca2+

Mg2+

Al3+

Zn2+

Metal oxide + Acid Salts + Hydrogen Less electropositive metals cannot displace hydrogen

ion from acid.

Cu2+

/Ag+

Metal carbonate + Acid Salts + Water + Carbon dioxide

metal carbonate is a solid that cannot dissolve in

water, in reaction that solid must be added excessively

All except Na+/K+/NH4

+

EXTRA INFO TO REMEMBERReactive metals are magnesium, aluminium, and zinc. Less

reactive metals are iron, lead, silver

Metals that are less reactive from hydrogen such as copper and silver do not react with dilute acid.

Soluble salts with sodium, potassium and ammonium ions can be prepared through neutralisation.

Do not use nitric acid because it can act as oxidising agent and form complicated products.

Metal, metal oxides and metal carbonates are solids that cannot dissolve in water. So, during the reaction the solids above must be added excessively to make sure all the hydrogen ions in acid are completely reacted. Excess solid can be expelled through filtration.

Less reactive metals such as lead (Pb), copper (Cu), and silver (Ag) cannot react with dilute acid. So, to prepare salt containing lead ions (Pb2+), copper ions (Cu2+) or silver ions (Ag+), we must use either oxide powder or carbonate powder only.

Impure soluble salt can be purified through crystallization process

EXTRA INFO TO REMEMBER