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Group member Chuah Rui Han
Christina Loh
Farah
Faliq Haziq
Faez
4
CEKAL
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8.1 SALTS
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Many different types of salts can be foundin nature.
There are various types of salts from the seasuch as sodium chloride, potassiumchloride, magnesium sulphate andpotassium chloride.
The earth·s crust is made up of mineralscontaining various types of salts such ascalcium fluoride, magnesium sulphate,
lead(II) sulphide and calcium carbonate.
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Agriculture
Chemical fertilisers
Pesticides
Medical Field
Medicines
Plasters
Food Industry
Flavouring
Preservatives
Chemical IndustryPlastic
Detergents
Plasters
Glass
Paintsdyes
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Salt is a compound formed when the
hydrogen ion in an acid is replaced by a
metal ion or an ammonium ion. A salt is formed in a neutralisation
reaction between an acid and a base.
Asalt is an ionic compound consisting ofa cation such as metal ion or an
ammonium ion from a base and ananion from an acid.
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Salts are ionic compounds and they can dissolve in water.
However, through experiments done by chemists, not all saltsare soluble in water.
Type of salts Soluble Insoluble
Ammonium salts All ammonium salts. -
Sodium and potassium salts All sodium and potassium salts. -
Ethanoate salts All ethanoate salts. -
Nitrate salts All nitrate salts. -
Sulphate salts All sulphate salts. except PbSO4, CaSO4, BaSO4
and Ag2SO4.
Chloride salts All chloride salts. except AgCl, HgCl and PbCl2.
Carbonate salts All carbonate salts. except Na2CO3, K 2CO3 and
(NH4)2CO3
Lead(II) salts All lead(II) salts. except Pb(NO3)2 andPb(CH3COO)2
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A soluble salt can be prepared from a
reaction between an acid and a metal,
a base or a carbonate.
Soluble salts
- Sodium salts
- Potassium salts
- Ammoniumsalts
Acid + alkali salt + water
Other salts
Acid + metal oxide salt + water
Acid + metal salt + hydrogen gas
Acid + metal carbonate salt +
water + carbon dioxide
Reactions involved in the
preparation of salts.
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The salts formed
contains impurities.
Therefore,
recrystallisation is
carried out to obtain pure
crystals of the salts(purified) from the
solution.
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The salt is prepared by titration method ofacid and alkali using an indicator.
Acid + Alkali Salt + Water
A titration is conducted to determine thevolume of acid needed to neutralise a fixed
volume of an alkali with the aid of anindicator.
The same volume of acid is then added tothe same volume of alkali without any
indicator to obtain pure and neutral saltsolution.
- The salt solution is gently heated toevaporate the solution to 1/3 its original
volume, producing a saturated solution.- Dip in a glass rod, if crystals are formed, the
solution is saturated.
- The solution is cooled at room temperature.
- The solution is filtered and dried the residueby pressing it between filter papers.
- The crystals are placed in a beaker.
- Distilled water is added to cover the crystals. The mixture is gently heated while stirring with aglass rod. More distilled water is added a little at a time until all crystals are dissolved.
- The solution is filtered to remove impurities.
- The solution is evaporated to 1/3 its original volume to obtain a saturated salt solution.
- The solution is cooled at room temperature.
- The solution is filtered and dried the residue by pressing it between filter papers.
RECRYSTALLISATION
CRYSTALLISATION NEUTRALISATION REACTION
TITRATION METHOD
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The salt is prepared by reacting acidwith insoluble metal/metal/metalhydroxide
Acid + metal salt + hydrogen
Acid + metal oxide salt + water
Acid + metal oxide salt + water
Acid + metal carbonate salt + water + carbon
dioxide
Add metal/metal oxide/metalcarbonate powder until excessinto a fixed volume of the heated
acidFilter the mixture to remove excess
solid (residue)
The salt solution is gently heated toevaporate the solution to 1/3 its
original volume, producing asaturated solution.
Dip in a glass rod, if crystals areformed, the solution is saturated.
The solution is cooled at roomtemperature.
The solution is filtered and dried theresidue by pressing it between filter
papers.
- The crystals are placed in a beaker.
- Distilled water is added to cover the crystals.The mixture is gently heated while stirring with
a glass rod. More distilled water is added alittle at a time until all crystals are dissolved.
- The solution is filtered to remove impurities.
- The solution is evaporated to 1/3 its originalvolume to obtain a saturated salt solution.
- The solution is cooled at room temperature.
- The solution is filtered and dried the residue
by pressing it between filter papers.
RECRYSTALLISATION CRYSTALLISATION
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Crystals has the following PHYSICAL CHARACTERISTICS:
(i) Fixed
geometricalshape (cuboid,
rhombic or
prism)
(ii) Fixed angle
between 2
adjacentsurfaces
(iii) Flat surfaces,
straight edgesand sharp
corners
EXPLANATION
Particles in a crystal are arranged in an orderly manner, closely-packed, incontact and at fixed positions.
The orderly arrangement is extended repeatedly throughout the three-
dimensional crystal lattice to give the overall shape of the crystal and also the
characteristics of (ii) and (iii).
The pattern of orderly arrangement of the particles is not the same in crystals of
different substances. This gives rise to different geometrical shapes of crystals.
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An insoluble salt is prepared throughPRECIPITATION REACTION through aDOUBLE DECOMPOSITION REACTION.
In this reaction, 2 aqueous solutions of
two different soluble salts are mixedtogether to form the insoluble salt.
The insoluble salt is formed as a
precipitate and can be obtained byFILTRATION.
The first solution must have a soluble saltwhich contains the CATION of theinsoluble salt.
The second solution must have a solublesalt which contains the ANION of the
insoluble salt.
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1. Mix 2 solutions containing cations and
anions of insoluble salts.
2. Stir with glass rod.3. Filter the mixture using filter funnel.
4. Rinse the residue with distilled water.
5. Dry the residue by pressing it betweenfilter papers.
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Chemical and ionic equations can be writtenfor all reactions that are used to prepare salts.
Example:
Barium sulphate, BaSO
4BaCl2(aq) + Na2SO4(aq) BaSO4(s) +
2NaCl(aq)
Ba2+ + 2Cl- + 2Na+ + SO42- BaSO4 + 2Na+
+ 2Cl-
Therefore, an ionic equation of the reaction is
formed:
Ba2+ + SO42- BaSO4(s)
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The ionic equation for the formation of an
insoluble salt can be constructed if we know
the number of moles of cation and anionreacted to form 1 mole of the insoluble salt.
For example, 1 mole of silver chromate(VI) isformed from 2 moles of Ag+ ions and 1 mole
of Cr O42- ions.
This can be determined form experiment by a
continuous variation method.
Pb2+(aq) + 2Br -(aq) PbBr 2(s)
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Use the ratio to construct the ionic equation.
Determine the simplest mole ratio of reactant A to reactant B whichcombine to form one mole of the insoluble salt.
Use the results of the experiment to calculate the number of moles ofreactant A and number of moles of reactant B which reacted
completely with each other.
Determine the volume of reactant B required to react completely
with the fixed volume of reactant A
Carry out a reaction between a fixed volume of reactant A withvarying volumes of a second reactant B
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A balanced chemical equation can be used to calculate the stoichiometricquantities of masses of reactants, volume & concentrations of reactants,masses of products and volumes of products.
The calculation steps involved are:
STEP
1
Write a balanced equation.
STEP 2
Write the information from the question above the equation.
STEP 3
Write the information from the chemical equation below the equation.(thenumber of moles of reactants/products).
STEP 4
Change the information in STEP 2 into moles by using method shown in thenext slide.
STEP 5
Use the relationship between number of moles of substance involved inSTEP 3 to find the answer.
STEP 6
Change the information to the unit required using the method shown in
the next slide.
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*EXAMPLES*
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In Chemistry, qualitative analysis is a
chemical technique used to determine what substances are
present in a mixture but not their quantities.
Therefore, in qualitative analysis of salts, we need to identifythe ions that are present in salts.
This can be done by analysing their physical and chemical
properties.
Observations on the
physical properties of salts
Action of heat on salts
Tests for cations and anions
Confirmatory tests for
cations and anions
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Observation on the
physical properties of salt
is carried out in order to
help us to infer certaincations and anions that
are present in the salts.
The observation is donein order to narrow down
the choices of cations and
anions present in a salt.
PHYSICALPROPERTIES
OF SALT
Colour
Solubilityof salts in
water
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Salt
Colour
Solid Aqueoussolution
Potassium salts
Sodium salts
Ammonium salts
Aluminium salts
Calcium salts
Lead(II) salts
Zinc salts
(with colourless anions)
White Colourless
Carbonate salts
Chloride salts
Nitrate salts
Sulphate salts
(with colourless cations)
White Colourless
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Iron(II) salts
[EX: Iron(II) chloride ,
Iron(II) nitrate , Iron(II)sulphate]
Green Green
Iron(III) salts
[EX: Iron(III) chloride ,
Iron(III) nitrate ,
Iron(III) sulphate]
Brown Brown
Iron(III) salts
[EX: Copper(II)
chloride , Copper(II)
nitrate , Copper(II)
sulphate]
Blue Blue
Copper(II) carbonate Green (Insoluble)
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COMPOUND SOLUBILITY IN WATER
Sodium,potassium and
ammonium salts
All are soluble
Nitrate salts All are soluble
Ethanoate salts All are soluble
Chloride salts All are soluble except AgCl, HgCl and PbCl2
Sulphate salts All are soluble except BaSO4, PbSO4 and CaSO4
Carbonate salts All are insoluble except Na2CO3, K2CO3 and
(NH4)2CO3
Metal oxides All are insoluble except Na2O, K2O and CaO(slightly soluble)
Metal hydroxides All are insoluble except NaOH, KOH, and Ba(OH)2
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Heating a salt may cause it to decompose. The decomposition may
result in:
- a colour change - evolution of a gas - liberation of watervapour
Gases such as carbon dioxide, oxygen, ammonia and nitrogen
dioxide can be evolved. By identifying the gas/gases liberated, it is
possible to pinpoint the anion present in the salt.
Examination of the residue can provide information to identify the
cation in the salt.
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Carbonate salt Colour of salt
before
heating
Colour of residue Action of Heat/Effect on
limewaterHot Cold
Copper(II)
carbonate
Green Black Black Decompose to produce metal oxide
& carbon dioxide.
Limewater turns milky.
Sodium carbonate White - - Does not decompose.
No change.
Potassiumcarbonate White - -
Does not decompose.
No change.
Calcium
carbonate
White White White Decompose to produce metal oxide
& carbon dioxide.
Limewater turns milky.
Magnesium
carbonate
White White White Decompose to produce metal oxide
& carbon dioxide.Limewater turns milky.
Zinc carbonate White Yellow White Decompose to produce metal oxide
& carbon dioxide.
Limewater turns milky.
Lead(II)
carbonate
White Brown Yellow Decompose to produce metal oxide
& carbon dioxide.
Limewater turns milky.
ACTION OF HEAT ON CARBONATE SALTS
Most METAL C ARBONATES
decompose on heating to produce
METAL OXIDES & C ARBONDIOXIDE gas.
Metal carbonate metal oxide +
carbon dioxide
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Alkali metal carbonates such as sodiumcarbonate and potassium carbonate arestable to heat (does not decompose).
Most metal carbonates decompose on heatingto produce metal oxides and liberate carbondioxide gas.
The carbon dioxide gas forms a whiteprecipitate with limewater, making thelimewater milky.
CONCLUSION:Heating a metal carbonate will decompose it into a
metal oxide and liberate carbon dioxide. Group 1
metal carbonates are not decomposed by heat.
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Nitrate salt Colour of salt
before
heating
Colour of residue Tests for gases evolved
Hot Cold Colour of
gas
Glowing
splinter
Blue
litmus paper
Copper(II) nitrate Blue Black Black Brown gas
&
colourless
gas
Rekindles Turns red
Sodium nitrate White White White Colourless Rekindles No change
Potassium nitrate White White White Colourless Rekindles No change
Calcium nitrate White White White Brown gas
&
colourlessgas
Rekindles Turns red
Magnesium
nitrate
White White White Brown gas
&
colourless
gas
Rekindles Turns red
ACTION OF HEAT ON NITRATE SALTS
Most METAL NITRATES decompose
on heating to produce METAL
OXIDES, NITROGEN DIOXIDE &OXYGEN gas.
Metal nitrate metal oxide +
nitrogen dioxide + oxygen
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Zinc nitrate White Yellow White Brown gas &
colourless gas
R ekindles Turns red
Iron(II) nitrate Green Black Black Brown gas & colourless
gas
Rekindles Turns red
Iron(III) nitrate Brown Brown Brown Brown gas & colourless
gas
Rekindles Turns red
Lead(II) nitrate White Brown Yellow Brown gas & colourless
gas
Rekindles Turns red
When nitrate salts are heated, they decompose to
liberate nitrogen dioxide and oxygen.
Only sodium nitrate and potassium nitrate decomposeto liberate oxygen.
Nitrogen dioxide is a acidic, brown gas that turns
moist blue litmus paper red.
Oxygen is a colourless gas that relights a glowing
wooden splinter.
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When a salt is dissolved in water, the free anion will be pesent in
the aqueous solution. Tests can then be carried out to identify
the anion.Anion Procedure Observation/Inference/
Ionic Equation
Carbonate
ion, CO32-
2cm3 of dilute hydrochloric acid/nitric acid/sulphuric
acid is added to 2cm3 of carbonate salt.
The gas given off is passed through lime water.
Effervescence occurs and the
lime water turns chalky.
The gas is carbon dioxide.
Ionic equation: CO32-(aq)+2H+(aq)
CO2(g)+H2O(l)
Chloride
ion, Cl-2cm3 of dilute nitric acid is added to 2cm3 solution of
chloride ions followed by 2cm3 of silver nitrate
solution.
A white precipitate is formed.
The precipitate is silver chloride.Ionic equation: Ag+(aq)+Cl-(aq)
AgCl(s)
Sulphate
ion, SO42-
2cm3 of dilute hydrochloric/nitric acid is added to
2cm3 of sulphate solution followed by 2cm3 of barium
chloride solution/barium nitrate solution.
A white precipitate is formed.
The precipitate is barium sulphate.
Ionic equation: Ba2+(aq)+SO42-(aq)
BaSO4(s)
Nitrate
ion, NO3-
2cm3 of dilute sulphuric acid is added to 2cm3 of
iron(II) sulphate solution.
The mixture is shaken.
The test tube is slanted and held with a test tube
holder.
A few drops of concentrated sulphuric acid is dropped along the wall of the test tube and is held
A brown ring is formed between two
layers.
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Cations Sodium hydroxide solution Ammonia solution
Small amount excess Small amount excess
K+ No change No change No change No change
Na+ No change No change No change No change
Ca2+ White precipitate Insoluble in excess No change No change
Mg2+ White precipitate Insoluble in excess White precipitate Insoluble in excess
Zn2+ White precipitate Soluble in excess White precipitate Soluble in excess
Al3+ White precipitate Soluble in excess White precipitate Insoluble in excess
Pb2+ White precipitate Soluble in excess White precipitate Insoluble in excess
Fe2+ Green precipitate Insoluble in excess Green precipitate Insoluble in excess
Fe3+ Brown precipitate Insoluble in excess Brown precipitate Insoluble in excess
Cu2+ Blue precipitate Insoluble in excess Blue precipitate Soluble in excess
NH4+ No change No change No change No change
Confirmatory tests are carried out by adding a small amount of sodium hydroxide solution / ammonia solution followed by excess
sodium hydroxide solution / ammonia solution to the solutionscontain the cations.
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Al3+ and Pb2+ are differentiated by double composition reaction.
An aqueous solution containing SO42-/Cl-/I- anion is used to detect
the presence of Al3+ and Pb2+.
Precipitate is formed when solution containing SO42-/Cl-/I- added
to Pb2+.
No precipitate is formed when solution containing SO42-
/Cl-
/I-
added to Al3+.
Condition Al3+ Pb2+
Add sodium
sulphate solution
No change White precipitate
Add sodium
chloride solution
No change White precipitate
Add potassium
iodide solution
No change White precipitate
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