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1. STUDYSMART
CHEMISTRY FORM 4
CHAPTER 8 : SALTS
8.1 Synthesising Salts
8.2 Synthesising qualitative analysis of salts
8.3 Practising to be systematic and meticulous when carrying
out activities
8.1 SYNTHESISING SALTS
A salt is a compound formed when the hydrogen
ion, H+ from an acid is replaced by a metal ion
or an ammonium ion, NH4+
Examples
HCl + NaOH  NaCl + H2O
2HNO3 + Zn  Zn(NO3)2 + H2
H2SO4 + MgCO3  MgSO4 + H2O + CO2
Complete the table below
Metal Sulphate salt Chloride salt Nitric Acid Carbonate salt
Ion (From H2SO4) (From HCl) (From HNO3) (From H2CO3)
Na+
K+
Zn2+
Mg2+
Ca2+
Fe2+
Fe3+
Cu2+
NH4+
Ba2+
Al3+
Pb2+
Ag2+
INSOLUBLE SALT
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2. Solubility of salt.
All K+ , Na+ and NH4+ salts are soluble
All nitrate salts are soluble
All carbonate are soluble except K2CO3, Na2CO3 and (NH4)2CO3
All Sulphate salts are soluble except BaSO4 , CaSO4, and PbSO4
All chloride salts are soluble except AgCl2 and PbCl2
The preparation of salt on its solubility of the salt and the nature of the reaction.
Preparation of salt
METHOD 3
Soluble Insoluble
METHOD 1 METHOD 2
K+ , Na+ NH4+ Other than K+ , Na+ - Mix two solution containing cations and
NH4+ salts anions of insoluble salts
- Stir using glass rod
Acid + Alkali  Salt + H2O - Filter using filter funnel
Acid + basic oxide  Salt + water - Rinse the residue with distilled water
Acid + metal  Salt + Hydrogen gas - Dry the residue with filter paper
Titration of acid and alkali
Acid + Metal Carbonate  Salt + Water + CO2
- Add acid to the alkali until it is neutral
with the aid of an indicator - Add basic oxide fillings/metals/metal carbonate to the acid and heat
- Repeat the procedure without using an it until some of it no longer dissolves. (This mean all acid has reacted
indicator with the basic oxide/metal/metal carbonate)
- Filter to move excess solid residue
2
2
- Gently heat the filtrate to obtain a saturated solution (one-third of its original volume remains)
- Cool the hot saturated solution to allow it to crystallize
- Filter and dry the crystals by using filter paper Study Smart
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3. TRY THIS 1
Write all possible chemical equation to prepare soluble salts and chemical equation for insoluble salt
*******KEY*******
S = SOLUBLE SALT
IS = INSOLUBLE SALT
SALT SOLUBILITY CHEMICAL EQUATION
Zinc Chloride
Sodium
Nitrate
Silver Chloride
Copper(II)
Sulphate
Lead(II)
Sulphate
Aluminium
Nitrate
Lead(II)
Chloride
Magnesium
Nitrate
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4. Potassium
Chloride
Lead(II)
Nitrate
Barium
Sulphate
Ammonium
Sulphate
Numerical problem involving stoichiometry reactions in the preparation of salts
A student prepare copper(II) nitrate, Cu(NO3)2 by reacting copper(II) oxide, CuO with 100 cm3 of 1.5
mol dm-3 nitric acid, HNO3. Calculate the mass of copper(II) oxide, CuO needed to react
completely with the acid. [RAM : Cu,64 ; O,16]
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5. 8.2 SYNTHESISING QUALITATIVE ANALYSIS OF SALTS
Colour of Salts
SOLID AQUEOUS SOLID/METAL OXIDE
White salt Colourless
Green Insoluble
Light Green Light Green
Blue Blue
Brown Brown
Black Insoluble
Yellow when hot Insoluble
White when cold
Brown when hot Insoluble
Yellow when cold
Confirmatory test for several gases
GAS COLOUR SMELL EFFECT ON REAGENT CONFIRMATORY TEST
DAMP USED
LITMUS
PAPER
Hydrogen Colourless Odourless No effect Lighted Bring a lighted splinter to the
splinter mouth of test tube. It gives
“pop” sound
Oxygen Colourless Odourless No effect Glowing Bring a glowing splinter to the
Splinter mouth of test tube. The
glowing splinter lights up
Carbon Colourless Odourless Blue  red Lime water Bubble the gas produce into
Dioxide lime water. Lime water will
turns chalky/milky/cloudy
Ammonia Colourless Pungent Red  blue Concentrated Dip a glass rod into
Smell HCl concentrated HCl. White
fumes is released
Chlorine Greenish Pungent Blue  red - -
yellow Smell  white
Nitrogen Brown Pungent Blue  red - -
Dioxide Smell
Sulphur Colourless Pungent Blue  red Acidified Turns acidified potassium
dioxide Smell potassium manganate (VII) solution from
manganate(VII) purple to colourless
solution
Hydrogen Colourless Pungent Blue  red Concentrated Dip a glass rod into
chloride Smell ammonia, NH3 Concentrated ammonia, NH3,
aqueous white fumes is released
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6. Action of heat on salts
a) Most compound which decomposes leave behind oxides
Salt metal oxide + gas
(residue identification (gas identification
refers to specific cations refers to anion)
only)
b)
Types of gas Colourless
released residue
Can predict the Can predict the
identify of anions identify of cations
presence in salt presence in salt
c) Test of carbon dioxide gas liberated when the carbonate salt is heated strongly
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7. d) Write down the chemical equation for the reactions that occur.
Ion Carbonate Salt Nitrate Salt
Is not decomposed by heat Decompose into O2 gas and metal nitrate
K+
Na+
Ca2+
Decompose into metallic oxide and CO2 Decompose into metal oxide, NO2 and O2
2+
Mg
Al3+
Zn2+
Fe2+
Fe3+
Pb2+
Cu2+
Sulphate salts usually do not decompose
Chloride salts do not decompose except NH4Cl
NH4Cl (s) NH3 (g) + HCl (g) [sublimation]
Confirmatory test for anions
Unknown Salt Solution
+ H2SO4 dilute
+ dilute +HNO3 + HNO3 + FeSO4
acid + AgNO3 + Ba(NO3)2 + H2SO4 conc
Gas turns __________ __________ ________
limewater Precipitate precipitate
__________ formed formed
________
__
Confirmatory test for cations
a) The presence of cation can be detected by using two common bench alkalis namely
i) _____________________________ solution
ii) _____________________________ solution
b) Write the ionic equation for the reaction of cations and sodium hydroxide
The function of the alkalis is to produce a precipitate that is
Metal hydroxide
METAL + HYDROXIDE ION  METAL HYDROXIDE
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8. Ion Ionic equation for the reaction of cations and sodium hydroxide
Aluminium ion Al3+ + 3OH-  Al(OH)3
Lead (II) Ion
Zinc Ion
Magnesium Ion
Calcium Ion
Copper (II) Ion
Ferrum (II) Ion
Ferrum (III) Ion
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9. NH4+ Ca2+ , Fe2+ ,,Fe3+ , Zn2+ , Al3+, Pb2+
Cu2+ , Mg2+
No Formation of Formation of white Fe2+ ,
Fe3+
Precipitate precipitation & precipitate & then K2Fe(II)(CN)6 Light Blue Blue
Non-soluble in soluble in excess precipitate precipitate
excess K2Fe(III)(CN)6 Dark Blue Brown
Precipitate Solution
+NaOH a little KSCN No Change Red solution
and then in
excess
+ HCl, white precipitate
CATIONS TEST
occurs and dissolved in
+NH4OH a little Fe2+ Fe3+ hot water
and then in
excess
NH4+, Ca2+ Fe2+ ,,Fe3+, Al3+ Zn2+ Cu2+ Confirmatory test Pb2+
Pb2+, Mg2+ ,
No Formation of precipitate is
Precipitate precipitation & formed & dissolve
Not dissolve in in excess + KI, yellow precipitate
excess NH4+ occurs and dissolved in
ION TEST hot water
Anion to be test:
Examples CO32- SO42- Cl- NO3-
+ Nessler reagent, brown
Anion Test Observation precipitate is form
CO32- + HCl Gas form white
precipitate with lime ANION TEST
water
Pre-Test
SO42- + HCl White precipitate is
+ BaCl2/ Ba(NO3)2 formed
Cl- + HNO3 White precipitate is
+ Ag(NO3)2 formed Confirmatory test Gas evolved from the
NO3- + H2SO4 (Dil) Brown ring is formed reaction with salt
+ FeSO4 9
+ H2SO4 (conc)
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10. Test for cations
Cations Test with a small amount of NaOH solution Test with a small amount of NH4OH until in
until in excess excess
Al3+ White precipitate soluble in excess. NaOH White precipitate, insoluble in excess NH4OH
solution solution
Pb2+ White precipitate, soluble in excess NaOH White precipitate, insoluble in excess NH4OH
solution solution
Zn2+ White precipitate, soluble in excess NaOH White precipitate, soluble in excess NH4OH
solution solution
Mg2+ White precipitate, insoluble in excess NaOH White precipitate, insoluble in excess NH4OH
solution solution
Ca2+ White precipitate, insoluble in excess NaOH No precipitate
solution
Cu2+ Blue precipitate, insoluble in excess NaOH Blue precipitate, soluble in excess NH4OH
solution solution
Fe2+ Green precipitate, insoluble in excess NaOH Green precipitate, insoluble in excess NH4OH
solution solution
Fe3+ Brown precipitate, insoluble in excess Brown precipitate, insoluble in excess NH4OH
NaOH solution solution
NH4+ No precipitate No precipitate
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