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SALTSWhat is salt?
Inthe preparation of salts, we must identify the type of salt. This can be done by analysing thecations and the anions that are present in salts.
Two types of salts
Soluble salt salts that can be dissolve in water at room temperature
Insoluble salt salts cannot be dissolve in water at room temperature
Type of salt Solubility in water
Sodium saltsPotassium saltsAmmonium salts
All dissolves in water
Nitrate salts All dissolves in water
Chloride saltsAll dissolves in water, Except: Lead(II) chloride, PbCl2
Silver chloride, AgClMercury chloride, HgCl
Sulphate saltsAll dissolves in water Except: Lead(II) sulphate, PbSO4
Barium sulfat, BaSO4Calcium sulfat, CaSO4
Carbonate salts
All did not dissolves in water, Except: Sodium carbonate, Na2CO3Potassium carbonate, K2CO3Ammonium carbonate, (NH4)2CO3
Special Properties of lead(II) chloride and lead(II) iodideNOTES: Lead halide such as lead(II) chloride (PbCl2), lead(II) bromide (PbBr2), and
lead(II) iodide (PbI2) did not dissolve in cold water but dissolve in hot water.
1
White precipitate of
PbCl2
White precipitate
dissolves in hotwater
White precipitate formedwhen the water is cooled
down.
Salt is an ionic compound formed when the hydrogen ion, H+ from acid is
replaced by a metal ion or ammonium ion, NH4
+
PbCl2 are soluble inhot water.
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Use of salts;
Item Use Example
Food preparation
FlavorMonosodium glutamate (MSG)
Sodium chloride
Preservatives
Sodium chloride - salted fish
Sodium benzoate - sauce
Sodium nitrite - processed meat, burger
Baking powder Sodium hydrogen carbonate
AgricultureNitrogen fertilizers
Potassium nitrate
Sodium nitrate
PesticideCopper(II) sulphate
Iron(II) sulphate
Medicine
Reduce stomach acidic(gastric)
Calcium carbonate
Calcium hydrogen carbonate
Sniff salt (fainted) Ammonium carbonate
Plaster of Paris (cementto support broken bone)
Calcium sulphate
A. Preparation of SaltThe procedure of preparation salt depends to the type of salt.
a. Insoluble salt is prepared through precipitation reaction.
b. Soluble salt is prepared by one of these reactions;
i. Acid and alkali
ii. Acid and metal oxide
iii. Acid and metal carbonate
iv. Acid and reactive metal
2
Yellow precipitate ofPbI
2
Yellow crystals formed when
the water is cooled down.Yellow precipitatedissolves in hot water
PbI2
are also soluble
in hot water.
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a. Insoluble Salts
i. Preparing Insoluble Salts1. Insoluble salts can be prepared through precipitation reactions ordouble decomposition reactions.2. Precipitation or double decomposition reaction involves;
- 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 insolublesalt orprecipitate, 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.
- the residue/precipitate (insoluble salt) then rinsed with distilled water to remove any other
ions as impurities.
3
Na+ Na+
NO3
-NO
3
-
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
Anion
(Non-metal ion)
Cation
(Metal ion)nn mm
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Chemical and ionic equations
Chemical equation : MX(aq) + NY(aq) MY(s) + NX(aq)solution solution precipitate solution
Ionic equation : M+(aq) + Y-(aq) MY(s)
Study this reaction carefully
In the formation of the precipitate of barium sulphate, BaSO4, the chemical equation can be written:
BaCl2(aq) + Na2SO4 (aq) BaSO4(s) + 2NaCl (aq)
Ions Ba2+ + Cl- + Na+ + SO42- BaSO4 + Na+ + Cl-
Ionic equation : Ba2+ + SO42- BaSO4
(shows the ions that take part in the reaction to form precipitate/insoluble salts)
More examples;
Insoluble Salt Ions Ionic equation
ZnCO3 Zn2+ , CO3
2- Zn2+ + CO32- ZnCO3
AgCl Ag+ , Cl- Ag+ + Cl- AgCl
BaSO4 Ba2+ , SO4
2- Ba2+ + SO42 BaSO4
PbCl2 Pb2+ , Cl- Pb2+ + Cl- PbCl2
PbSO4 Pb2+ , SO4
2- Pb2+ + SO42- PbSO4
CaCO3 Ca2+ , CO3
2- Ca2+ + CO32- CaCO3
4
Glass rod
Residue/precipitate(Insoluble salt)
Filtrate(Soluble salt)
Mixture of solutions
Filter funnel
Filter paper
Retort stand
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ii. Preparation and purification of insoluble salts
Preparation of Plumbum(II) iodide
Chemical equation : Pb(NO3)2 (aq) + 2KI (aq) PbI2 (s) + 2KNO3 (aq)
Ionic equation : Pb2+ (aq) + 2I- (aq) PbI2 (s)
Step 1: Preparation
1. 20 cm3 lead(II) nitrate 0.1 mol dm-3 solution is measured with measuring cylinder 50 ml,
and poured into a beaker.2. 20 cm3 potassium iodide 0.1 mol dm-3 solution is measured with measuring cylinder 50 ml
and poured into a beaker contains lead(II) nitrate solution.
3. The mixture is stirred with a glass rod. A yellow precipitate is formed.
4. The mixture is filtered to obtain the yellow solids of lead(II) iodide as the residue.
5
+
20 cm3
Lead(II) nitrat
0.1 mol dm-3
20 cm3
potassium iodide
0.1 mol dm-3
Glass rod
Precipitate of lead(II) iodide
(yellow)
Sodium nitrate solution
Mixture of solutions
Filter funnel
Filter paper
Retort standBeaker
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Step 2: Purification
5. The residue is rinsed with distilled water to remove other ions in it.
6. The yellow solid is dried by pressing between two pieces of filter paper.
EASY LAH !
6
Glass rodDistilled water
Precipitate of lead(II)iodide
Precipitate of lead(II)
iodideFilter paper
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b. Soluble Salt
i. Preparaing Soluble Salt
- Sodium salts
-
Potassium salts Acid + alkali salts + water
- Ammonium salts
Soluble Salts
Acid + metal oxide salts + water
- Others salts Acid + reactive metal salts + hydrogen gas
Acid + metal carbonate salt + water + carbon dioxide
Notes: Reactive metal is magnesium, aluminium, and zinc
Unreactive metal is iron, lead, silver
a. Sodium, potassium or ammonium salts prepared from acid and alkali reaction.
Salt Alkali Acid Chemical equation
NaCl NaOH HCl NaOH + HCl NaCl + H2O
K2SO4 KOH H2SO4 2KOH + H2SO4 K2SO4 + 2H2O
NH4NO3 NH3/NH4OH HNO3 NH3 + HNO3 NH4NO3 + H2O
CH3COONa NaOH CH3COOH NaOH + CH3COOH CH3COONa + H2O
Note: To prepare the above salts, titration technique is use.
b. Soluble salt (except sodium, potassium and ammonium salt) is prepared using these methods
- Acid and metal
- Acid and metal oxide- Acid and metal carbonate
Name of SaltAcid that must be
used
Substance that can be use to react with acid
Metal Metal oxide Metal carbonate
ZnCl2 HCl Zn ZnO ZnCO3
Mg(NO)3 HNO3 Mg MgO MgCO3
CuSO4 H2SO4 CuO CuCO3
7
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Pb(NO3)2 HNO3 PbO PbCO3
Write a chemical equation for each experiment above.
Remember this notes ok1. Metal that is lessreactive from hydrogen such as copper, lead and
silver/argentum didnot react with dilute acid.2. Metal, metal oxide and metal carbonate above is a solid that cannot dissolves in
water, hence during reaction that solid must be added excessively to make sureall hydrogen ions in acid is completely reacted. Excess solid can be expelling
through filtration.
3. Impure soluble salt can be purified through crystallization process.
ii. Preparation and purification of soluble salts
A. Preparing soluble salt through reaction between acid and alkali.
Preparation of Soluble Sodium, Potassium and ammonium Salts
Soluble salts of sodium, potassium and ammonium can be prepared by the reaction between an
acid and alkali.
Acid (aq) + alkali (aq) Salt (aq) + Water (l)Procedure :
Using pipette, 25 cm3 of alkali solution is measured and
transferred into a conical flask.
Two drops of phenolphthalein are added to the alkali solution. Dilute acid is place in a burette. The initial reading is recorded.
Acid is added slowly into the alkali solution while shaking
the conical flaks, until the pink solution turn colourless.
The final reading of the burette is recorded.
The volume of acid added, V cm3 is calculated.
The experiment is repeated by adding V cm3 of acid to
25 cm3 of alkali solution in a beaker without usingphenolphthalein as an indicator.
The mixture is transferred into a evaporating dish.
The mixture is heated until saturated and the saturated solution
is allowed to cool at room temperature. Salt crystals formed are filtered and rinsed with a little of cold distilled water.
Salt crystals are dried by pressing it between filter papers (or in oven)
The reaction between acid and alkali is known as what process?
Refer to acids and bases notes ok. Dont worry Ill help you.!
Kita bukan along kita cuma nak tolong.
8
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Example: Preparing sodium chloride
Step 1:Preparation (Titration)
1. 25.0 cm3 sodium hydroxide solutions is pipette into conical flask.
2. Two drops of phenolphthalein indicator are added into conical flask. The colour of solution is
recorded.
3. A 50 cm3 burette is filled with hydrochloric acid. The initial burette reading is recorded.4. Hydrochloric acid is added gradually from a burette into conical flask and swirling the conical
flask.5. Titration is stopped when phenolphthalein changes from pink to colourless. The final burette
reading is recorded.
6. The volume of hydrochloric acid used is calculated.
7. The experiment is repeated by adding hydrochloric acid (known volume) to 25.0 cm3 sodiumhydroxide in a beaker without using phenolphthalein.
Step 2: Preparation (Crystallization)
9
Retort
stand
Burette
Hydrochloric acid
Conical flask
25 cm3 NaOH + phenolphthalein
indicator
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8. The mixture is transferred into a evaporating dish.
9. The colourless solution is slowly heated/evaporated until its saturated or to about one-third (1/3)
of the original volume.10. The saturated solution is then cooled to allow crystallization to occur.
Step 3: Purification
10. The white crystals formed are then filtered, rinsed with a little distilled
water and dried by pressing between filter paper.
Note: Phenolphthalein indicator is used at the beginning of the experiment to determine the volume
of hydrochloric acid that is required to react completely with 25 cm3 of sodium hydroxide.
However experiment is repeated without using phenolphthalein so that the salt prepared willnot contaminated by the indicator.
10
Bunsen burner
Evaporating dishSalt solution
Glass rodDistilled water
Copper(II) sulphate
Filter funnel
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B. Preparing soluble salt through reaction between acid
i. Metal oxide. ii. Metal iii. Metal carbonate
Procedure To Prepare a Soluble Salt (not Na, K or NH4+)
50 cm3 of acid is measured using a measuring cylinder and poured into a beaker. The acid is
heated slowly.
Using a spatula, metal / metal oxide / metal carbonate powder is added a little at a time whilestirring the mixture with a glass rod.
The addition of the solid powder is stopped when some solids no longer dissolve anymore. (the
solid is excess and all the acid is completely neutralised by the solid)
The mixture is filtered to remove the excess solid powder.
The filtrate is transferred to an evaporating dish.
The filtrate is heated until saturated. (The filtrate is evaporated to about one-third (1/3) of theoriginal volume)
11
Heat ing
AcidP o w d e r
o f :
M etal ox ide
M etal carbonM e t a l
Excess of solid powd
Filtrate (Salt solution)
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The saturated solution is then allowed to cool to room temperature and the salt crystals are
formed.
The crystals are filtered and rinsed with a little cold distilled water.
Salt crystals are then dried by pressing it between filter papers.
Example: Preparing copper(II) sulphate
(Sulphuric acid and copper(II) oxide powder)
Step 1: Preparation
1. 50 cm3 sulphuric acid 0.1 mol dm-3 is put in a beaker and is heated.
2. Using spatula copper(II) oxide powder is added a little at a time to the hot sulphuric acid while
stirring continuously with glass rod.3. The addition of copper(II) oxide is stopped when solids powder remain undissolved.
12
xxxxxxxxxxxxxxxx
Copper(II) oxide
Glass rod
Beaker
Wire gauze
50 cm3 sulphuric acid 0.1 mol dm-3
TripodBunsen burner
Spatula
Stir
H ea t ing
S a t u r a t e d s o l u t io n
C ry sta
F i l tra te
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4. The mixture is filtered to remove the excess copper(II) oxide.
5. The filtrate is transferred to an evaporating dish.
6. The filtrate is slowly heated/evaporated until its saturated, or to about one-third (1/3) of theoriginal volume.
7. The saturated solution is then allowed to cool to room temperature.
Step 3: Purification
13
Glass rod
Reactant mixture
Excess copper(II) oxide
Copper(II) sulphate solution
Bunsen burner
Evaporating dish
Copper(II) sulphatesolution
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8. The crystals are filtered and rinsed with a little cold distilled water.
9. Salt crystals are then dried by pressing it between filter papers.
REMEMBER. THIS NOTES OK
Unreactive metal such as lead (Pb), copper (Cu), and silver (Ag) cannot react with
dilute asid. So to prepare salt contains lead ions (Pb2+), copper ions (Cu2+)or silver ions (Ag+), we must use eitheroxide powder orcarbonate powder only.
Example: CuO + H2SO4 CuSO4 + H2O (ok)
CuCO3 + H2SO4 CuSO4 + H2O + CO2 (ok)
Cu + H2SO4 no reaction (not ok)
B. Physical Characteristics of Crystals.
A salt is made upof positive and negative ions. When these ions are packed closely
with a regular and repeated arrangement in an orderly manner, a solid withdefinite geometry known as crystal lattice is formed.
All crystals have these physical characteristics:a) Reqular geometry shapes, such as cubic or hexagonal.
b) Flat faces, straight edges and sharp angles.
c) Same angle between adjacent faces.d) All crystals of the same salt have the same shape although the sizes may be different.
14
Glass rod
Distilled water
Copper(II) sulphate
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Start to memorize the solubility of a salt in water OK.It will help you a lot to better understand this chapter.
KNOWLEDGE IS POWER
The solubility of a salt in water depends on the types ofcations and anions present.
C. Qualitative
Analysis ofSalts
What is Qualitative
analysis?
Inthe
qualitative analysis of salts, we need to identify the ions that are present in salts. Thiscan be done by analysing theirphysical and chemical properties.
Observations on the physical properties of salts
1. Colour and solubility in water
Certain physical properties of salts such colour and solubitity in water are observed to help us infer certain cations
and anions that are present in salts.The table shows the colour of salts in solid , in aqueous solution and the solubility of salts in water
Salt Colour in solidSolubility inwater
Colour in Aqueous solution
1. Ammonium chloride NH4Cl white soluble colourless
2. Ammonium nitrateNH4(NO3)3 white soluble colourless
15
Salt Solubility in water
Sodium, potassium and
ammonium salts(Na+, K+, NH4+)
All are soluble
Nitrate salt (NO3-) All are soluble
Chloride salt (Cl-) All chloride salts are soluble in waterexcept
PbCl2, AgCl andHgCl2
Sulphate salt (SO42-)
All sulphate salts are soluble in waterexcept
PbSO4, BaSO4andCaSO4
Carbonate salt (CO32-) All carbonate salts are insolubleexcept Na2CO3,
K2CO3 and(NH4)2CO3
Qualitative analysis is a chemical technique used to determine
substances are present in a mixture but not their quantitie
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3. Calcium carbonate CaCO3 white insoluble -
4. Calcium nitrate Ca(NO3)2 white soluble colourless
5. Magnesium sulphate MgSO4 white soluble colourless
6. Magnesium carbonate MgCO3 white insoluble -
7. Zinc sulphate Zn SO4 white soluble colourless
8. Zinc nitrate Zn(NO3)2 white soluble colourless9. Lead(II) chloride , PbCl2 white insoluble -
10. Lead(II) sulphate , PbSO4 white insoluble -
11. Lead(II) carbonate , PbCO3 white insoluble -
12. Copper(II) chloride , CuCl2 Blue soluble Blue
13 Copper(II) sulphate , PbSO4 Blue soluble Blue
14. Copper(II) carbonate , PbCO3 Green insoluble -
15. Iron(II) sulphate , FeSO4 Green soluble Pale green
16. Iron(III) chloride , FeCl3 Brown / Yellow soluble Brown/Yellow/ Yellowish brown
17. Sodium nitrate , NaNO3 white soluble colourless
18, Sodium carbonate , Na2CO3 white soluble colourless
19. Potassium nitrate , KNO3 white soluble colourless
20. Potassium carbonate , K2CO3 white soluble colourless
The table shows the colour of different cations in the solid form or in aqueous solution
Observation Inference
Blue solution Ion copper (Cu2+ ) present
Pale green solution Ion Iron(II) Fe2+ present
Yellow/Yellowish-brown/brown solution
Ion Iron (III) Fe3+ present
Green solid Hydrated Fe 2+, CuCO3
Brown solid Hydrated Fe 3+ salt
White solidSalts of Na+ , K+ ,NH4
+, Mg 2+, Ca 2+ Al 3+ , Zn 2+, Pb 2+ (If the anions are
colourless
Colourless solution Na+ , K+ ,NH4+, Mg 2+, Ca 2+ , Al 3+ , Zn 2+, Pb 2+
The table shows the solubility of different types of salts in water
Compounds Solubility in water
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Sodium saltsPotassium salts
Ammonium saltsAll are soluble
Nitrate saltsAll are soluble
Chloride saltsAll are soluble except AgCl, HgCl and PbCl2 (soluble in hot water)
Sulphate saltsAll are soluble except BaSO4, PbSO4 and CaSO4
Carbonate salts All are insoluble except sodium carbonate, potassium carbonate andammonium carbonate
2. Tests for gases
Gases are often produced from reactions carried out during laboratory tests on salts. By identifying the gasesevolved,it is possible to infer the types of cations and anions that are present in a salt.
The table shows the test and the result of different gases
Gas Test Result
Oxygen gas, O2Test with a glowing woodensplinter
Wooden splinter is rekindled /lighted
Hydrogen gas , H2Test with a lighted woodensplinter
Gas explodes with a pop sound
Carbon dioxide gas , CO2Bubble the gas produced intolime water
Lime water turns milky
Ammonia gas, NH3Test with moist red litmuspaper
Moist red litmus paper turns blue
Chlorine gas, Cl2Test with moist blue litmuspaper
Moist blue litmus paper turns red and thenturns white
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Hydrogen chlorine gas , HClTest with a drop ofconcentrated ammonia NH3solution
Dense white fumes
Sulphur dioxide gas , SO2
Bubble the gas produced intopurple acidified potassiummanganate (VII), KMnO4solution
Purple acidified potassium manganate(VII),KMnO4 solution decolourises
Nitrogen dioxide gas , NO2Test with moist blue litmuspaper
moist blue litmus paper turns red
3. Action of heat on salts
Effect of heat on carbonate salts
Carbonaate saltColour of salt
before heating
Colour of residueEffect on lime water
Hot cold
Copper (II)carbonate, CuCO3
Green powder Black powder Black powder The gas liberated turnslime water milky/chalky
Zinc carbonate ,ZnCO3
White solid Yelow solid White solidThe gas liberated turnslime water milky/chalky
Lead(II) carbonate,PbCO3
White solid Brown sold Yelow solidThe gas liberated turnslime water milky/chalky
Sodium carbonate,Na2CO3
White solid White solid White solid No change
Calcium carbonate,CaCO3
White solid White solid White solidThe gas liberated turnslime water milky/chalky
Potassiumcarbonate, K2CO3
White solid White solid White solid No change
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Magnesiumcarbonate, MgCO3
White solid White solid White solidThe gas liberated turnslime water milky/chalky
Effect of heat on nitrate salts
Nitrate Salt Colour of saltbefore heating
Colour of residueTest on gases liberated
Hot cold
Copper (II) nitrate,Cu(NO3)2
Blue solidBlackpowder
Blackpowder
A brown gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
Zinc nitrate,Zn(NO3)2
White solidYellowsolid
White solid
A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
Lead(II) nitrate,Pb(NO3)2
White solid Brown solidYellowsolid
A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowing
splinter
Sodium nitrate,NaNO3
White solid White solid White solidA colourless gas that rekindles aglowing splinter is liberated
Calcium nitrate,Ca(NO3)2
White solid White solid White solid
A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
Potassium nitrate,KNO3
White solid White solid White solidA colourless gas that rekindles aglowing splinter is liberated
Magnesium nitrate,Mg(NO3)2
White solid White solid White solidA browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
Iron(II) nitrate,Fe(NO3)2
Pale Green solidPale Greensolid
PaleGreensolid
A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
Iron(III) nitrate,Fe(NO3)3
Brown solidReddish-Brown solid
Reddish-Brownsolid
A browan gas that turns blue litmuspaper red is liberated.The gas liberated also ignites a glowingsplinter
The table shows the comparison of the effect of heat on carbonate and nitrate salts
Metal Effect of heat on carbonate salt Effect of heat on nitrate salt
PotassiumSodium
Are not decomposed by heat Decompose to nitrite salt and oxygen gas.
CalciumMagnesium
AluminiumZincIron
Decompose to metal oxide andcarbon dioxide gas.
Decompose to metal oxide, nitrogen dioxidegas and oxygen gas.
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TinLeadCopper
MercurySilverGold
Decompose to metal, carbondioxide gas and oxygen gas.
Decompose to metal , nitrogen dioxide gasand oxygen gas.
Most sulphate salts are not decomposed by heat. Only a few sulphate such as iron(II) sulphate,zinc sulphate andcopper sulphate decompose to sulphur dioxide or sulphur trioxide gas when heated.
All chloride salts are stable when heated except ammonium chloride. Ammonium chloride sublimes anddecomposes to produce ammonia gas and hydrogen chloride gas.
The table shows the deduction of the types of ion present based on the gas produced
Type of gas produced Type of ion present(anion)
CO2 Carbonate ion (CO32- ) present except Na2CO3 and K2CO3
O2 Nitrate ion (NO3-) present
NO2 Nitrate ion (NO3-) present except NaNO3 and KNO3
SO2 Sulphate ion (SO42- ) present
NH3 Ammonim ion (NH4+) present
Tests for anions
Reagent / Condition Observation Anion Ionic Equation (if any)
2 cm3 the unknown solution +dilute hydrochloric acid / nitric
acid / sulphuric acid pourinto a test tube gas liberatedis immediately bubbled throughlime water.
Effervescence.Colourless gasturns lime watermilky.
CO32- ion CO3
2- + 2H+ CO2 +H2O
2 cm3 of nitric acid + 2 cm3 of
the unknown solution pourinto a test tube
+ 2 cm
3
silvernitrate solution
White precipitateis formed.
Cl- ion Ag+ + Cl- AgCl
2 cm3 of dilute hydrochloric acid/ nitric acid + 2 cm3 of the
unknown solution pour into atest tube + 2 cm3 of bariumchloride / barium nitrate solution
shake well
White precipitateis formed.
SO42- ion Ba2+ + SO4
2 - BaSO4
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2 cm3 of the unknown solution
pour into a test tube2 cm3 of dilute sulphuric acid +2 cm3 of iron(II) sulphate
solution shake well.Then drop carefully and slowly
a few drops of concentratedsulphuric acid along the side ofa slanting test tube into themixture without shaking it.
Brown ring isformed at theboundarybetween theconcentratedH2SO4 (top layer)
and aqueoussolution of themixture (bottomlayer)
NO3- ion -
Tests for cations
Confirmatory Test for Fe2+, Fe3+, Pb2+, NH4+ Ions
Confirmatory Test for Fe2+
Reagent Observation Conclusion
Potassium hexacyanoferrate(II)solution
Pale blue precipitate Fe2+ ion is present
Dark blue precipitate Fe3+ ion is present
Potassiumhexacyanoferrate(III) solution
Dark blue precipitate Fe2+ ion is present
Greenish-brown solution Fe3+ ion is present
Potassium thiocyanate solution Pale red colouration Fe2+ ion is present
Blood red colouration Fe3+ ion is present
Confirmatory Test for Pb2+
Method Observation Ionic Equation
Using aqueous solution of chloride- 2 cm3 of any solution of Cl-+
2 cm3 of any solution of Pb2+dilute with 5 cm3 of distilled waterheat until no further change occursallow the content to cool to roomtemperature using running water from
- A white precipitate isformed
When heated dissolve inwater to form colourlesssolution
Pb2+ + 2Cl- PbCl2
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the tap
When cooled whiteprecipitate reappear
Using aqueous solution of iodide- 2 cm3 of any solution of I- +
2 cm3 of any solution of Pb2+dilute with 5 cm3 of distilled waterheat until no further change occursallow the content to cool to roomtemperature using running water fromthe tap
- A yellow precipitate isformed
When heated dissolve in
water to form colourlesssolution
When cooled yellowprecipitate reappear
Pb2+ + 2I- PbI2
Confirmatory Test for NH4+
Method Observation
2 cm3 of any solution of NH4+ + 2 cm3 of
NaOH / KOH / Ca(OH)2
heat
put apiece of moist red litmus paper at the mouthof the test tube
- Moist red litmus paper turns blue
Reaction with Nesslers Reagent
2 cm3 of any solution of NH4+ + 2 cm3 of
Nesslers Reagent shake well
- A brown precipitate is formed
Reaction of Cations With NaOH
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Pb2+ Zn2+ Al3+ : White precipitate dissolves/larut in excess NaOHCa2+ Mg2+ : White precipitate insoluble/tidak larut in excess NaOH
Reaction of Cations With NH3
23
Cations
+ NaOH (aq)
Precipitate producedNo precipitate
White precipitate Coloured precipitate
Green Blue Brown
Fe2+ Cu2+ Fe2+NH
4
+K+ Na+
Dissolve in excessNaOH (aq) to formcolourless solution
Sodium hydroxide solution is pouredslowly into 2 cm3 of the solution to betested in a test tube, until in excess.
Insoluble inexcessNaOH (aq)
NH3
gas produced
warm
Zn2+
Al3+
Pb2+
Ca2+
Mg2+
Easylah
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Zn2+ : White precipitate dissolves/larut in excess NH3Pb2+Al3+ Mg2+ : White precipitate insoluble/tidak larut in excess NH3
24
Cations
Precipitate producedNo precipitate
White precipitate Coloured precipitate
Green Blue Brown
Fe2+ Cu2+ Fe2+NH
4
+K+ Na+
Aqueous ammonia solution is pouredslowly into 2 cm3 of the solution to betested in a test tube until in excess.
NH3
gas produced
warm
Zn2+
Al3+
Pb2+
Ca2+
Mg2+
Easylah
+ NH3
(aq)
+ excessNH
3(aq)
Dark bluesolution
Dissolve in excessNH
3(aq) to form
colourless solution
Insoluble inexcess NH
3(aq)
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Zn2+ ion is the only cation that form white precipitate and dissolves in
both excess NaOH and NH3 solutions.
Mg2+ ion is the only cation that form white precipitate and insoluble in
both excess NaOH and NH3 solutions.
Ca2+ ion in the only cation that form white precipitate in NaOH
solutions, but no precipitate in NH3 solution.
Fe2+ , Fe3+ and Cu2+ ions is easy to spot because the ions shows
coloured precipitate.
Pb2+ ion and Al3+ ion form white precipitate and dissolves in excess
NaOHsolution, but insoluble in excess NH3 solutions.
Example: lead(II) nitrate solution and aluminium nitrate solution
Sodium sulphate solution is added slowly into 2 cm3 of the solution to be tested in atest tube.If a white precipitate is formed, then then the solution tested is lead(II) nitrate.If no change occurs, then the solution tested is aluminium nitrate.
25
Based from the observation, I can conclude that
How to differentiate between Pb2+ and Al3+?
A chemical tests can be carried out in
the laboratory to differentiate between
Pb2+ and Al3+.
(Please refer to Confirmatory Test for
Pb2+, in ealier notes).
Now let see some questions about salt.
Try to solve it by yourself first and then
compare with the answers provided.
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Example 1:
Describe chemical tests that can be carried out in the laboratory to differentiate between
(a) lead(II) nitrate solution and aluminium nitrate solution
Sodium sulphate solution is added slowly into 2 cm3 of the solution to be tested in a test tube.If a white precipitate is formed, then then the solution tested is lead(II) nitrate.If no change occurs, then the solution tested is aluminium nitrate.
(b) aluminium nitrate solution and zinc nitrate solution
Aqueous ammonia solution is pouredslowly into 2 cm3 of the solution to be tested in a test tubeuntil in excess.If a white precipitate that dissolves in excess aqueous ammonia solution is formed, than thesolution tested is zinc nitrate.If a white precipitate that is insoluble in excess aqueous ammonia solution is formed, than thesolution tested is aluminium nitrate.
(c) ammonium chloride solution and potassium chloride solution
Nesslers Reagent is added to 2 cm3 of the solution to be tested in a test tube.
If a brown precipitate is formed, then the solution tested is ammonium chloride.If no change occurs, then the solution tested is potassium chloride
(d) iron(II) sulphate solution and iron(III) sulphate solution
Potassium hexacyanoferrate(II) solution is poured into 2 cm3 of the solution to be tested in atest tube.If a dark blue precipitate is formed, then the solution tested is iron(III) chloride.If no change occurs, then the solution tested is iron(II) chloride.
Or
Potassium hexacyanoferrate(III) solution is poured into 2 cm3
of the solution to be tested in atest tube.If a greenish-brown solution is formed, then the solution tested is iron(III) chloride.If no change occurs, then the solution tested is iron(II) chloride.
Or
Potassium thiocyanate solution is poured into 2 cm3 of the solution to be tested in a test tube.If a blood red colouration is formed, then the solution tested is iron(III) chloride.If no change occurs, then the solution tested is iron(II) chloride.
26
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(e) sodium chloride and sodium sulphate
Silver nitrate solution is poured into 2 cm3 of the solution to be tested in a test tube.If a white precipitate is formed, then the solution tested is sodium chloride.If no change occurs, then the solution tested is sodium sulphate.
Or
Barium chloride solution is poured into 2 cm3 of the solution to be tested in a test tube.If a white precipitate is formed, then the solution tested is sodium sulphate.If no change occurs, then the solution tested is sodium chloride.
Example 2:
1. State three examples ofa) soluble salts b) insoluble salts
Potassium carbonate Magnesium carbonateLead(II) nitrate Lead(II) sulphateAmmonium chloride Argentum chloride
2. Which of the following salts is soluble
3. Identify the gas that turns moist red litmus paper blue
Ammonia gas
4. Gas X has the following properties
Gas X is carbon dioxide gas
5. Heat +
27
Lead(II) chloride Sodium carbonate
Calcium sulphate Barium sulphate
Colourless
Acidic gas
Turns lime water milky
Salt P Metal oxide X Gas Y
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Colour of metal oxide X is yellow when hot and white when cold. Gas Y turns lime water milky.
a) Name gas Y : carbon dioxide gas
b) Name metal oxide X : zinc oxide
c)Name salt P : zinc carbonate
d) Write an equation to represent the action of heat on salt P
ZnCO3 (s) ZnO (s) + CO2 (g)
6. A sample of copper(II) nitrate, Cu(NO3)2 was heated strongly. Write down the expected observation.
Copper(II) nitrate decompose to produce black colour of residue when hot and cold. A browngas that changed moist blue litmus paper to red and colourless gas that lighted up a glowing
wooden splinter are produced.
D. Numerical problem involving stoichiometric reaction in the
preparation of salt
28
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Example 1;
Ammonium phosphate, (NH4)3PO4 is use as a fertilizer. 29.8g of this salt is prepared by neutralizingphosphoric acid, H3PO4 with ammonium gas, NH3. Calculate the volume of ammonium gas, NH3 reacted
at room conditions.
( Relative atomic mass; H, 1: N, 14: P, 31; O, 16; Molar volume; 24 dm3 mol-1 at room conditions)
Solutions;
a. Calculate the number of moles
2.88 g
[3(14) + 12(1) + 31 + 4(16)
= 0.2 mol
b. Write a balanced chemical equation
Compare the mole ratio of NH3 and(NH4)3PO4
H3PO4(aq) + 3NH3(aq) (NH4)3PO4(aq)
c. Calculate the number of moles of NH3 base onthe mole ratio
= 3 X 0.2 mol
= 0.6 mol
d. Calculate the volume of NH3
Volume = number of mole X volume
= 0.6 mol X 24 dm3 mol -1
= 14.4 dm3
Example 2:
3.9 g of potassium is burnt completely in the air as shown in the following equation;
4K(s) + O2(g) 2K2O(s)
29
A balanced chemical equation for a reaction in preparation of a salt canbe used to calculate the stoichiometric quantities of the followingMasses of reactantsVolumes and concentrations of reactantsMasses of productsVolumes of products
=
3 mol 1 mol
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What is the mass of potassium oxide produced?[Relative atomic mass: K, 39; O, 16]
Solutions
Tip: Solve the question step by step
Step 1: Write Chemical Equation
4K(s) + O2(g) 2K2O(s)
4 mol of K react with 1 mol of O2 produce 2 mol K2O
Step 2:Calculate the number of mole
[Get the information from the question]
Step 3: Find the coefficient From Balance Chemical Equation
FBCE;
4 mol of K produce 2 mol K2O
Thus;
0.1 mol of K produce 2/4 mol K2O = 0.2 mol K2O
FBCE;
[Sebelah kiri] [Sebelah kanan]Bil. mol yang telah dikira Bil. Mol yang hendak ditentukan
4 mol K = 2 mol K 2O
0.1mol K = 2/4 x 0.1mol K 2O = 0.05 mol K2O
No. of mol of K2O = 0.05 mol
Step 4: Solve the questionsThus;Mass of K2O = 0.05 mol Molar mass
= 0.05 mol 55 g mol-1
= 2.75 g
Example 3:
Acids reacts with calcium carbonate, CaCO3 in limestone to form a salt and carbon dioxide, CO2.
A piece of limestone reacted completely with 100 cm3 of 31.5 g dm-3 nitric acid, HNO3.
30
No. of mol K
=mass
Molar mass
=3.9 g
39 gmol-1
0.1 mol=
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[Relative atomic mass: H, 1; C, 12; N, 14; O, 16; Ca, 40. Molar volume: 24 dm3 mol-1 at roomconditions]
a. Calculate the mass of salt produced.
b. What is the volume of carbon dioxide, CO2 liberated at room conditions?
Step 1: Write Chemical Equation
Chemical Equation: 2HNO3 + CaCO3 Ca(NO3)2 + CO2 + H2O
Step 2:Calculate the number of mole
Get the information from the question;
FBCE; 2HNO3 + CaCO3 Ca(NO3)2 + CO2 + H2O
2 mol HNO3 = 1 mol Ca(NO3)2
0.05 mol HNO3 = x 0.05 mol Ca(NO3)2 = 0.025 mol Ca(NO3)2
No. of mol of Ca(NO3)2 = 0.025 mol
Mass of Ca(NO3)2 = 0.025 mol 40 + 2[14 + 3(16)] g mol-1
= 4.1 g
FBCE; 2HNO3 + CaCO3 Ca(NO3)2 + CO2 + H2O
31
No. of mole ofHNO3
=Molarity Volume
1000
=
0.5 mol dm-3 100 cm3
1000
= 0.05 mol
Concentration of HNO3 = 31.5 g dm
3
=Molar mass ofHNO
3
31.5 g dm3
= 0.5 mol dm-3
= 31.5 g dm3
1 + 14 + 48 g mol-1
Change theconcentration
given in g dm-3
to mol dm-3 first
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2 mol HNO3 = 1 mol CO2
0.05 mol HNO3 = x 0.05 mol CO2 = 0.025 mol CO2
No. of mol of CO2 = 0.025 mol
Volume of CO2 = 0.025 mol 12 + 2(16) dm3 mol-1= 1.1 dm3
Example 4:
Pb(NO3)2 compound decomposes when heated as shown in the following equation.
If 6.62 g of Pb(NO3)2 compound is heated, calculate;
[Relative atomic mass: N, 14; O, 16; Pb, 207; 1 mol of gas occupies 22.4 dm3 at s.t.p.](i) mass of PbO that is produced
(ii) volume of nitrogen dioxide produced at s.t.p
(ii) volume of oxygen produced at s.t.p
Solution:
FBCE; 2Pb(NO3)2 2PbO + 4NO2 + O2
2 mol Pb(NO3)2 = 2 mol PbO
0.02 mol Pb(NO3)2 = 0.02 mol PbO
No of mol PbO = 0.02 mol
Mass of PbO = 0.02 x 223 = 4.46 g
FBCE; 2Pb(NO3)2 2PbO + 4NO2 + O2
32
No of mol Pb(NO3)
2
=mass
Molar mass
=6.62 g
331 gmol-1
0.02 mol=
2Pb(NO3)2 2PbO + 4NO2 + O2
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2 mol Pb(NO3)2 = 4 mol NO2
0.02 mol Pb(NO3)2 = 4/2 x 0.02 mol O2 = 0.04 mol O2
No of mol O2 = 0.04 mol
Volume of O2 = 0.04 x 22.4 dm
3
= 0.896 dm3 // 896 cm3
FBCE; 2Pb(NO3)2 2PbO + 4NO2 + O2
2 mol Pb(NO3)2 = 1 mol O2
0.02 mol Pb(NO3)2 = x 0.02 mol O2 = 0.01 mol O2
No of mol O2 = 0.01 mol
Volume of O2 = 0.01 x 22.4 dm3
= 0.224 dm3 // 224 cm3
Numerical Problems involving stoichiometric reactions in the precipitation of salts
Question 1:
A student prepare copper(II) nitrate, Cu(NO3)2 by reacting copper(II) oxide, CuO with 200 cm3 of 2.0
moldm-3 nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to react completely with
the acid.
[Relative atomic mass: Cu, 64 ; O, 16]
Question 2:
X cm3 of 0.5 moldm-3 sulphuric acid, H2SO4 is added to 100 cm3 of 1.0 moldm-3 lead(II) nitrate solution
to produce lead(II) sulphate, PbSO4.
[Relative atomic mass: Pb, 20; O, 16; S, 32]
Calculate the value of X.Calculate the mass of lead(II) sulphate obtained.
Start to do exercises from any book.
I will help and guide you to master this topic.
Prepared by;
Kamal Ariffin Bin SaaimSMKDBL
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