6. Qualitative Analysis

Qualitative Analysis

Acids, Bases, and Salts

Prepared by: Ms Siti Soleha

Qualitative Analysis to
Identify Cations and Anions

in Salts

Qualitative analysis of a salt is a
technique used to identify the cation and
anion present in a salt by analysing its
physical and chemical properties.

Steps involved in the qualitative
analysis of a salt.

Observation on Effect of heat on
the physical the salt
properties of
the salt

Confirmatory Test for anions
tests for cations and cations

and anions

Observations of the Physical Properties of Salts

• Observing the physical properties of salts such as colour and solubility
in water is the first step to make inferences on the possibility of the
presence of cations and anions in the salt.

• Even though the solubility test of the salts does not confirm the
identities of the ions present, it helps us narrow down the possible
identities of the ions present

For example, salt X is soluble in water. Hence, salt X
might contain ANaK nitrate ions, but definitely not
PAH chloride or PCB sulphate and most probably

does not contain the carbonate ion, CO32–.

Observations of the Physical Properties of Salts

• All white soluble salts dissolve in water to form colourless salt
solutions. Salts form coloured solutions due to the presence of ions in
transition elements.

❖ Blue solution : possibly contains copper(II) ion, Cu2+
❖ Brown solution: possibly contains iron(III) ion, Fe3+
❖ Green solution : possibly contains iron(II) ion, Fe2+

Colour of salts in solid state and in aqueous
solution

Effect of Heat on Salts and Gas Tests

• Examples of qualitative analysis based on the effect of heat on salts X and Y and Salt X is a carbonate salt that
the corresponding gas tests. possibly contains Ca2+ ion, Mg2+
ion or Al3+ ion and not K+ ion or
• However, the qualitative analysis carried out could not identify the presence of Na+ ion because potassium
cation in the salts. carbonate and sodium carbonate
are not decomposed by heat.

Salt Y is a nitrate salt that possibly contains Ca2+ ion,
Mg2+ ion or Al3+ ion and not K+ ion and Na+ ion because
potassium nitrate and sodium nitrate do not produce a
brown gas.

Anion Tests

Only four anions are needed to be
identified at this level, which are:



Anion Tests Nitric acid, HNO3 and barium nitrate
solution, Ba(NO3)2 can replace

hydrochloric acid, HCl and barium
chloride solution, BaCl2 to test for the

presence of sulphate ion, SO42–.

• Bcaarsbeodnodniothxeidteesgtafsotrhtahtetucarnrbsolinmaetewiaotne,rCcOlo32u–dtyh.e reaction between acid and carbonate ions, CO32– produces

2H+(aq) + CO3 2–(aq) → CO2 (g) + H2O(l)
• In the test for chloride ion, Cl– , silver ion, Ag+ is used to detect the presence of chloride ions, Cl– .

• If chloride ions, Cl– is present, hence the white precipitate of silver chloride, AgCl is produced.

• Hfoorwmeavtieorn, tohfeacawrhbiotenaptreeicoipni,tCaOte32o–faslislovegrivceasrbthoenasatem, Aego2bCsOe3rv. ation when reacting with silver ion, Ag+ due to the

• Therefore, an excess of nitric acid, HNO3 has to be added before adding silver nitrate solution, AgNO3 .

• If effervescence occurs when nitric acid, HNO3 was added, then, the presence of carbonate ion, CO32– is
confirmed.

• However, if no effervescence occurs, the formation of white precipitate confirms the presence of the chloride ion,
Cl– .

• Freoarctthioentebsettowfeseunlpthhaetbeairoinu,mSOio42n–,, barium ion, Ba2+ used tSoOd42e–tepcrtotdhuecpesreaswenhcieteopf rseuclpiphiatateteioonf ,bSaOri4u2m– bseucalpuhsaetteh, e
BaSO4 . Ba2+ and sulphate ion,

• Hydrochloric acid, HCl iwonas, Cald-d, ethdaitnisextocedsestbeectfoarnedaedldiminignbataerituhme ccahrlboornidaetesoiolunt,iCoOn,3B2–atChla2tfomrigthhet same reason as
in the test for chloride be present.

Qualitative
analysis
based on
anion tests

Cation Tests

❖Alkalis such as sodium hydroxide solution, NaOH, and
ammonia solution, NH3 are two main reagents used to test the
presence of cations.

❖The hydroxide ion, OH– from both solutions combine with most
metal ions to form a precipitate of metal hydroxide.

❖Inference about the cations present can be made based on the
observation on the colour of the precipitate and its solubility in
an excess of alkali solution



Reactions between cations and sodium
hydroxide solution, NaOH

Reaction between cations and ammonia
solution, NH3

Example 1

Example 2

Confirmatory Tests for Cations

❖ Both Al3+ ion and Pb2+ ion give the same observations when
tested with sodium hydroxide solution, NaOH and ammonia
solution, NH3.

❖ Thus, a confirmatory test is required to differentiate between
Pb2+ ion and Al3+ ion.

❖ Other than that, ions such as Fe2+ , Fe3+ and NH4+ too can be
confirmed using specific reagents.





Confirmatory tests for NH4+ ion, Fe2+ ion
and Fe3+ ion

Chemistry
Lense

❖ Potassium hexacyanoferate(II) solution, K4Fe(CN)6 is used
to confirm the presence of iron(III) ion, Fe3+.

❖ If this solution is added to an aqueous solution that
contains iron(II) ion, Fe2+, a light blue precipitate is
formed.

❖ Potassium hexacyanoferate(III) solution, K3Fe(CN)6 is
used to confirm the presence of iron(II) ion, Fe2+ .

❖ If this solution is added to an aqueous solution containing
iron(III), Fe3+ , a greenish brown colour is obtained

Al3+ ion and Pb2+ ion form white precipitates that are insoluble
in an excess of alkali solution. Thus, potassium iodide
solution, KI is used to differentiate between these two ions.

Qualitative Analysis on Unknown Salts

Test yourself!

Thank You…