CHAPTER 8.2: QUALITATIVE ANALYSIS

NURUL ASHIKIN BT. ABD RAHMAN PART 6

Learning Outcome

State the meaning of qualitative analysis.

Make inferences on salts based on their colour and solubility in water.

Describe tests for the identification of gases.

What is qualitative analysis…???

Qualitative analysis is a chemical method to

determine the substances present in a compound but not their

quantities.

The ions present in salt are need to

identify in this qualitative analysis

Qualitative Analysis Steps

Observation physical properties of salts

Action of heat on salt

Make aqueous solution of the salt to test for anions and cations present

Carry out confirmatory tests

How to identify cation and anion in salt???

Click to add Title1 Colour and solubility of the salt1

Click to add Title2 Gas test2

Click to add Title1 Effect of heat on salt3

Click to add Title2 Confirmatory test for anions4

Click to add Title1 Confirmatory test for cations5

SALT COLOURSOLID AQUEOUS SOLUTION

Ca2+ , Mg 2+ , Al3+ , Pb2+ , NH4+ white colourless

CuSO4, Cu(NO3)2 Blue Blue

CuCl2 Green Blue

FeSO4, Fe(NO3)2, FeCl2 Green Green

Fe(SO4)3, Fe(NO3)3, FeCl3 Brown Yellow/BrownishCuCO3 Green (Insoluble)PbO Brown when Hot &

Yellow when cooledInsoluble

CuO black InsolubleZnO Yellow when Hot &

White when cooledInsoluble

PbCl2 white Insoluble in cold water but soluble in hot water

PbI2 Yellow Insoluble in cold water but soluble in hot water

Colour and solubility of the salt

ACTIVITY TO INVESTIGATE THE

COLOUR AND SOLUBILITY OF SALT

IN WATER

Gas TestGas Colour Smell Confimatory Test

O2colourless Odourless Light up a glowing wooden splinter

H2colourless Odourless Produces a ‘pop’sound with lighted wooden

CO2colourless Odourless Turn lime water cloudy

NH3colourless Pungent smell Turn moist red litmus paper blue

Cl2Grenish Yellow

Pungent smell Bleaches moist red litmus paperTurn moist blue LP to red and bleaches it.

HCl colourless Pungent smell Form dense white fumes with ammonia gas

NO2Brown Pungent smell Turn moist blue litmus paper to red

SO2colourless Pungent smell Turn moist blue litmus paper to red

Methods Used For Identifying

Gases

MEMORY TEST…

Learning Outcome Describe the action of heat on salts. Describe the tests for anions. State observation of reaction of cations with

sodium hydroxide solution and ammonia solution. Describe confirmatory tests for Fe2+ , Fe3+ ,Pb2+ and

NH4+

Plan qualitative analysis to identify salts.

Action Of Heat On Salts

A colour change Release a certain gas

Release of water vapour

When Salt are Heated

• All carbonates are decomposed by heat to release CO2 except K2CO3 and NaCO3.•MCO3 MO + CO2

• CO2 will turn lime water,Ca(OH)2 milky (CaCO3 +H2O)

•Most metal nitrate decompose to produce a metal oxide, nitrogen oxide and oxygen.• KNO3 & NaNO3 produced Oxygen gas and nitrites when

heated• NO2 (brown gas: acidic) , turn moist blue litmus paper

red.• O2 relight glowing wooden splinter.

Heating CO3 salt

Heating NO3 salt

• All suphate salt are not decomposed by heat.• Some (Fe, Zn, Cu) will decomposed during strong

heating producing sulphur trioxide gas.• Ex: ZnSO4 ZnO + SO3

• All chloride salts are not decomposed by heat except ammonium chloride.• NH4Cl produced white fumes.• Ex: NH4 NH3 + HCl

Heating SO4 salt

Heating Chloride salt

Deduction Of Types Of Ion Present From Gas Produced

Gas produced Types of ion

CO2 CO3 2- (except Na2CO3, K2CO3)

O2 NO3-

NO2 and O2 NO3- (excepts NaNO3, KNO3)

SO2 SO4 2-

NH3 NH4 +

Test for Anion

Anion Confirmatory TestCO3

2- • Bubbles with dilute acid and the gas produced will cause limewater milky

SO42- •Mixed with dilute sulphuric acid and

barium chloride and a white precipitate is formed.

Cl- •Mixed with dilute nitric acid followed by silver nitrate solution and a white precipitate is formed

NO3- • Brown ring test and a brown ring will be

formed.

Test for CationCation NaOH Solution NH3 Solution

Ca2+ • White precipitate formed.• Not soluble in excess

• No reaction

Mg2+ • White precipitate formed.• Not soluble in excess

• White precipitate formed.• Not soluble in excess

Al3+ • White precipitate formed.• Soluble in excess

• White precipitate formed.• Not soluble in excess

Zn2+ • White precipitate formed.• Soluble in excess

• White precipitate formed.• Soluble in excess

Cation NaOH Solution NH3 Solution

Pb2+ • White precipitate formed.• Soluble in excess

• White precipitate formed.• Not soluble in excess

Fe2+ • Green precipitate formed.• Not soluble in excess

• Green precipitate formed.• Not soluble in excess

Fe3+ • Brown precipitate formed.• Not Soluble in excess

• Brown precipitate formed.• Not soluble in excess

Cu2+ • Blue precipitate formed.• Not soluble in excess

• Blue precipitate formed.• Not Soluble in excess and a

dark blue solution is produced

NH4+ • White precipitate formed.

• Soluble in excess• No reaction

Confirmatory Tests for Fe2+ , Fe3+ ,Pb2+, NH4+

Cation Specific reagent Observation

Pb2+ • KI, NaI • Yellow precipitate, soluble in hot water and recrystallises when cooled

• KCl, NaCl,HCl • White precipitate, soluble in hot waterand recrystallises when cooled

• K2SO4, Na2SO4, H2SO4

• White precipitate, insoluble in hot water

Confirmatory Tests for Fe2+ , Fe3+ ,Pb2+, NH4+

Cation Specific reagent Observation

Fe2+ • Potassium hexacyanoferreta (II) K4Fe(CN)6

• Light blue precipitate

• Potassium hexacyanoferreta (III) K3Fe(CN)6

• Dark blue precipitate

• Acidified KMnO4 • Purple colour decolourises

Confirmatory Tests for Fe2+ , Fe3+ ,Pb2+, NH4+

Cation Specific reagent Observation

Fe3+ • Potassium thiocyanate, KSCN

• Brown precipitate formed.

• Not soluble in excess

• Potassium hexacyanoferrate (II) , K4Fe(CN)6

• Dark blue precipitate

• Potassium hexacyanoferrate (II) , K4Fe(CN)6

• Greenish-brown solution

NH4 + • Nessler reagent • Brown precipitate

AObservation on the physical properties of salt

BAction of heat on salt

CTest for cations and anions

DConfirmatory test for cation and anions

PLAN QUALITATIVE ANALYSIS TO IDENTIFY SALTS

End of slide… Thank you..

UPSI