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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
Ion
Sulphate salt
(From H2SO4)
Chloride salt
(From HCl)
Nitric Acid
(From HNO3)
Carbonate salt
(From H2CO3)
Na+
K+
Zn2+
Mg2+
Ca2+
Fe2+
Fe3+
Cu2+
NH4
+
Ba2+
Al3+
Pb2+
Ag2+
INSOLUBLE SALT
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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.
METHOD 3
METHOD 1 METHOD 2
2
Preparation of salt
Soluble Insoluble
K+
,Na+
NH4
+
Acid + Alkali Salt + H2O
Titration of acid and alkali
- Add acid to the alkali until it is neutral
with the aid of an indicator
- Repeat the procedure without using an
indicator
- 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
Other than K+
,Na+
NH4
+
salts
Acid + basic oxide Salt + water
Acid + metal Salt + Hydrogen gas
Acid + Metal Carbonate Salt + Water + CO2
- Add basic oxide fillings/metals/metal carbonate to the acid and heat
it until some of it no longer dissolves. (This mean all acid has reacted
with the basic oxide/metal/metal carbonate)
- Filter to move excess solid residue
- Mix two solution containing cations and
anions of insoluble salts
- Stir using glass rod
- Filter using filter funnel
- Rinse the residue with distilled water
- Dry the residue with filter paper
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TRY THIS 1
Write all possible chemical equation to prepare soluble salts and chemical equation for 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
*******KEY*******
S = SOLUBLE SALT
IS = INSOLUBLE SALT
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8.2 SYNTHESISING QUALITATIVE ANALYSIS OF SALTS
Colour of Salts
Confirmatory test for several gases
GAS COLOUR SMELL EFFECT ON
DAMP
LITMUS
PAPER
REAGENT
USED
CONFIRMATORY TEST
Hydrogen Colourless Odourless No effect Lighted
splinter
Bring a lighted splinter to the
mouth of test tube. It gives
“pop” sound
Oxygen Colourless Odourless No effect Glowing
Splinter
Bring a glowing splinter to the
mouth of test tube. The
glowing splinter lights up
Carbon
Dioxide
Colourless Odourless Blue red Lime water Bubble the gas produce into
lime water. Lime water will
turns chalky/milky/cloudy
Ammonia Colourless Pungent
Smell
Red blue Concentrated
HCl
Dip a glass rod into
concentrated HCl. White
fumes is released
Chlorine Greenish
yellow
Pungent
Smell
Blue red
white
- -
Nitrogen
Dioxide
Brown Pungent
Smell
Blue red - -
Sulphur
dioxide
Colourless Pungent
Smell
Blue red Acidified
potassium
manganate(VII)
solution
Turns acidified potassium
manganate (VII) solution from
purple to colourless
Hydrogen
chloride
Colourless Pungent
Smell
Blue red Concentrated
ammonia, NH3
aqueous
Dip a glass rod into
Concentrated ammonia, NH3,
white fumes is released
SOLID AQUEOUS SOLID/METAL OXIDE
White salt Colourless
Green Insoluble
Light Green Light Green
Blue Blue
Brown Brown
Black Insoluble
Yellow when hot
White when cold
Insoluble
Brown when hot
Yellow when cold
Insoluble
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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)
c) Test of carbon dioxide gas liberated when the carbonate salt is heated strongly
Types of gas
released
Can predict the
identify of anions
presence in salt
Colourless
residue
Can predict the
identify of cations
presence in salt
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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
Mg2+
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
+ H2SO4 dilute
+ dilute +HNO3 + HNO3 + FeSO4
acid + AgNO3 + Ba(NO3)2 + H2SO4 conc
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
Unknown Salt Solution
Gas turns
limewater
__________
__________
Precipitate
formed
__________
precipitate
formed
________
________
__
The function of the alkalis is to produce a precipitate that is
Metal hydroxide
METAL + HYDROXIDE ION METAL HYDROXIDE
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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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NH4
+
Ca2+
, Fe2+
,,
Fe3+
, Zn2+
, Al3+
, Pb2+
Cu2+
, Mg2+
No Formation of Formation of white
Precipitate precipitation & precipitate & then
Non-soluble in soluble in excess
excess
Fe2+ ,
Fe3+
K2Fe(II)(CN)6 Light Blue Blue
precipitate precipitate
K2Fe(III)(CN)6 Dark Blue Brown
Precipitate Solution
KSCN No Change Red solution+NaOH a little
and then in
excess
+NH4OH a little
and then in
excess
NH4
+
, Ca2+ Fe2+
,,
Fe3+
, Al3+
Zn2+
Cu2+
Pb2+
, Mg2+
No Formation of precipitate is
Precipitate precipitation & formed & dissolve
Not dissolve in in excess
excess
Examples
Anion Test Observation
CO3
2-
+ HCl Gas form white
precipitate with lime
water
SO4
2-
+ HCl White precipitate is
+ BaCl2/ Ba(NO3)2 formed
Cl-
+ HNO3 White precipitate is
+ Ag(NO3)2 formed
NO3
-
+ H2SO4 (Dil) Brown ring is formed
+ FeSO4
+ H2SO4 (conc)
Anion to be test:
CO3
2-
SO4
2-
Cl-
NO3
-
CATIONS TEST
Pre-Test
Confirmatory test
ION TEST
Gas evolved from the
reaction with salt
NH4
+
+ Nessler reagent, brown
precipitate is form
+ KI, yellow precipitate
occurs and dissolved in
hot water
Pb2+
,
+ HCl, white precipitate
occurs and dissolved in
hot waterFe2+
Fe3+
ANION TEST
Confirmatory test
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Test for cations
Cations Test with a small amount of NaOH solution
until in excess
Test with a small amount of NH4OH until in
excess
Al3+
White precipitate soluble in excess. NaOH
solution
White precipitate, insoluble in excess NH4OH
solution
Pb2+
White precipitate, soluble in excess NaOH
solution
White precipitate, insoluble in excess NH4OH
solution
Zn2+
White precipitate, soluble in excess NaOH
solution
White precipitate, soluble in excess NH4OH
solution
Mg2+
White precipitate, insoluble in excess NaOH
solution
White precipitate, insoluble in excess NH4OH
solution
Ca2+
White precipitate, insoluble in excess NaOH
solution
No precipitate
Cu2+
Blue precipitate, insoluble in excess NaOH
solution
Blue precipitate, soluble in excess NH4OH
solution
Fe2+
Green precipitate, insoluble in excess NaOH
solution
Green precipitate, insoluble in excess NH4OH
solution
Fe3+
Brown precipitate, insoluble in excess
NaOH solution
Brown precipitate, insoluble in excess NH4OH
solution
NH4
+
No precipitate No precipitate
