5. Effect of Heat on Salts

Effect of Heat on Salts

Acids, Bases, and Salts
Prepared by: Ms Siti Soleha

Gas Test

1. Put two spatulas of solid potassium chlorate(V),

KClO3 into a test tube.
2. Heat the solid with high heat.

Heat Test for Oxygen (O2) Gas

Method Observation Inference

1. Insert a glowing Glowing wooden Oxygen
wooden splinter into
the test tube splinter ignites/ supports

lights up combustion

1. Put some a few pieces of zinc powder, Zn into

a test tube.
2. Add 4 cm3 of dilute sulphuric acid, H2SO4 into

the test tube.

Test for Hydrogen (H2) Gas

Procedure Observation Inference

Place a lighted wooden ‘Pop’ sound Hydrogen
splinter near the mouth heard gas is a
of the test tube. flammable
gas.

1. Put a spatula of solid zinc

carbonate, ZnCO3 into a test tube.
2. Heat the solid with high heat.

Test for Carbon Dioxide (CO2) Gas

Procedure Observation Inference

1. Flow the gas Limewater change
produced into from colourless to
limewater chalky/cloudy

1. Put a spatula of solid ammonium chloride, NH4Cl into
a test tube.

2. Add 4 cm3 of dilute sodium hydroxide solution, NaOH

into the test tube.

3. Heat the mixture slowly.

Test for Ammonia(NH3) Gas

Procedure Observation Inference

Place a piece of moist red Moist red Ammonia is
an alkaline
litmus paper to the mouth of litmus paper gas

the test tube turns blue

1. Put a spatula of powdered manganate(IV) oxide,

MnO2 into a test tube.
2. Carefully add 2 cm3 of concentrated hydrochloric

acid, HCl.

3. Heat the mixture slowly.

4. Greenish yellow and pungent smell is produced

Test for Chlorine (Cl2) Gas

The greenish Procedure Observation Inference
yellow gas is
the chlorine Place a piece of moist Moist blue litmus Chlorine is
gas.
blue litmus paper to the paper turns red and an acidic

mouth of the test tube bleached. gas

1. Put a spatula of solid sodium chloride, NaCl into a test

tube.
2. Add 2 cm3 of concentrated sulphuric acid, H2SO4

carefully.

3. Heat the mixture slowly.

Test for Hydrogen Chloride (HCl) Gas

Procedure Observation Inference

1. Dip a glass rod into White fumes White fume is

concentrated ammonia are formed. NH4Cl
solution, NH3 .
2. Then, hold the dipped

glass rod to the mouth

of the test tube.

1. Put a spatula of solid sodium sulphite, Na2SO3
into a test tube.

2. Add 4 cm3 of dilute hydrochloric acid, HCl.

3. Heat the mixture slowly

Test for Sulphur Dioxide(SO2) Gas

Turns acidified Procedure Observation Inference
potassium
dichromate(VI) Flow the gas released Turns acidified
solution, K2Cr2O7
from orange to into acidified potassium potassium
green
manganate(VII) solution, manganate(VII)

KMnO4 . solution, KMnO4
from purple to

colorless.

1. Put a spatula of solid lead(II) nitrate, Pb(NO3)2 into a
test tube.

2. Heat the mixture with high heat

3. Brown gas produced.

Test for Nitrogen Dioxide(NO2) Gas

Procedure Observation Inference

The brown gas Place piece of moist blue Turns moist Nitrogen
is the nitrogen dioxide is an
dioxide gas. litmus paper to the blue litmus acidic gas

mouth of the test tube paper to red.

Effect of Heat on Salts

➢ Most salts decompose when heated.
➢ By comparing the colour of the salt and the

residue left behind and the gas released, we can
identify the cation and anion that might be present
in the salt

Action of Heat on Carbonate Salt
and Nitrate Salt

Action of Heat on Carbonate Salts

▪ When heated, most carbonate salts decompose
to produce metal oxides and carbon dioxide
gas.

▪ For example, decomposition of zinc carbonate
salt, ZnCO3 produces zinc oxide, ZnO and
carbon dioxide gas, CO2

Action of Heat on Nitrate Salts

▪ When heated, nitrate salts decompose to
produce metal oxides, nitrogen dioxide gas and
oxygen gas.

▪ The following equation shows the thermal
decomposition of lead(II) nitrate salt, Pb(NO3)2

▪ Only several sulphate salts and chloride salts will decompose
when heated.

▪ The cation or anion of a salt can be identified based on the
gases released when the salt undergoes thermal
decomposition.

Chemistry The cation presents in some salts can be
Lense identified from the colour of the residue
after heating.

Example

Test Yourself!

Thank you…