ACIDS, BASES AND SALTS
In our day-to-day life we use and see many things like lemon
juice, vinegar, chilly, baking soda, soap and detergent, milk,
orange, caustic soda etc. . Some of these things taste sour and
some bitter. This taste of the things is due to the presence of
acids or bases respectively in them. If someone in the family is
suffering from the problem of acidity due to overeating, we
suggest that person to have baking soda solution. This is
because baking soda is basic in nature and therefore it will
neutralize the effect of an acid giving relief to that person.
Indicators
An indicator is a substance which tells us whether the other
substance is an acid or a base by changing their colour and
smell.
Types Of Indicators
1. Indicators showing different colours in acidic and basic
media. (Colour indicators)
2. Indicators giving different ordour in acidic or basic media.
(Olfactory indicators)
Colour Indicators
(i) Natural Indicators
Litmus Solution
It is a purple coloured dye extracted from lichen plant.
Two types of litmus solutions are used as indicators they
are blue litmus which is obtained by acidifying the purple
litmus and red litmus which is obtained by making the
purple dye alkaline.
Acids turn blue litmus to red whereas bases turn red
litmus to blue.
(ii) Synthetic Indicators
They are methyl orange and phenolphthalein. These are
manufactured in the industry.
Acids turn phenolphthalein colourless whereas bases turn
it pink.
Acids turn methyl orange pink whereas bases turn it
yellow.
Olfactory Indicators
(i) Onion
(ii) Vanilla essence
(iii) Clove oil
The ordour of these substances change when acid or base
is added.
Acids
General Properties Of Acids
(i)
(ii)
(iii)
(iv)
(v)
Acids are sour in taste.
Acids turn blue litmus to red and methyl orange pink.
Acid are oily liquids.
Acids are drying and dehydrating in nature.
Acids can conduct electricity in their aqueous solutions.
Chemical Properties Of Acids
(i)
Reaction With Metals
Acids react with metals to form salts and hydrogen gas is
released.
Metal + Acid → Salt + Hydrogen gas
Zn + 2HCl → ZnCl 2 + H 2
Zn + H 2 SO 4 → ZnSO 4 + H 2
2 K + 2HCl → 2KCl + H 2
2 K + H 2 SO 4 → K 2 SO 4 + H 2
The above reactions are also called displacement reactions.
Note
Metals present in reactivity series below hydrogen do not react
with dilute acids.
(ii) Reaction With Metal Carbonates And Metal
Bicarbonates
Acids react with metal carbonates and metal bicarbonates
to give out carbon dioxide with effervescence (bubbles)
and forming the corresponding salt and water.
Metal carbonate + Acid → Metal salt + CO 2 +
and bicarbonate
H2O
K 2 CO 3 + HCl → KCl + H 2 O + CO 2
KHCO 3 HCl → KCl + H 2 O + CO 2
CaCO 3 + H 2 SO 4 → CaSO 4 + H 2 O + CO 2
2 Ca(HCO 3 ) 2 + 2 H 2 SO 4 → 2 CaSO 4 + 4 H 2 O + 4
CO 2
(iii) Reaction With Bases
Acids react with bases to form salt and water. These types
of reactions are called neutralization reactions.
Acid + Base → Salt + Water
HCl + NaOH → NaCl + H 2 O
(iv) Reaction With Metallic Oxides
As metallic oxides are also basic in nature therefore the
acids react with metallic oxides to form salt and water.
Metallic Oxide + Acid → Salt + Water
CuO + 2 HCl → CuCl 2 + H 2 O
Bases
General Properties Of Bases
(i)
(ii)
(iii)
(iv)
Bases are bitter in taste.
Bases turn red litmus to blue and methyl orange to yellow.
Bases are slippery or soapy to touch.
Some bases are also corrosive in nature; they cause
burning sensation like caustic soda.
(v) Bases conduct electricity in their aqueous solutions.
Chemical Properties Of Bases
(i)
Reaction With Metals
Some bases (strong) like sodium hydroxide and potassium
hydroxide react with strong active metals like aluminium
and zinc to form corresponding salt and water.
Base + Metal → Salt + Hydrogen Gas
2 NaOH + Zn → Na 2 ZnO 2 + H 2
2 NaOH + Al + 2H 2 O → 2NaAlO 2 + 3H 2
(ii) Reaction With Acids
Bases react with acids to form salt and water. This
reaction is also called neutralization reaction.
Base + Acid → Salt + Water
NaOH + HCl → NaCl + H 2 O
(iii) Reaction With Non Metallic Oxides
As non metallic oxides are acidic in nature, bases react
with them to form salt and water.
Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O
On passing excess of carbon dioxide the following reaction
takes place
CaCO 3 + H 2 O + CO 2 → Ca(HCO 3 ) 2
More About Acids And Bases
Chemical Nature Of Acids
Acids are the substances which contain hydrogen ions
(protons). These hydrogen ions in the form of hydrogen gas
are released out when acids react with active metals.
Conduction Of Electricity By Acids Or Bases
Acids in their aqueous solution conduct electricity. There are
many substances which have hydrogen in them but all of them
do not conduct electricity. It is because hydrogen is not
present in ionic form and these substances do not dissociate in
their aqueous solutions.
Example
Alcohol, Sugar
Acids release H+ ions only in the presence of water.
Experiment To Illustrate Conduction Of Electricity By
An Acid
(i) Take a rubber cork.
(ii) Fix two nails in it.
(iii) Place this cork in a 100 ml beaker.
(iv) Connect the nails to a 6 V battery with the help of wires.
(v) Connect a small torch bulb or an ammeter into the circuit.
(vi) Now add dilute sulphuric acid into the beaker so that the
nails are completely immersed.
(vii) Switch on the battery.
Observation
It is observed that the bulb starts glowing or the needle of the
ammeter shows deflection. This shows that dilute acids
conduct electricity.
Conduction Of Electricity By Bases
Bases in their aqueous solution conduct electricity.
Note
The compound C 2 H 5 OH (ethanol) contains –OH group. But it
does not ionize in the aqueous solution to give OH- ions. Hence
it is not a base.
Dilution OF Concentrated Bases
Just as dilution of concentrated acid is an exothermic process,
similarly if we dissolve bases like NaOH or KOH in water the
solution is found to be hotter. Therefore it is also an
exothermic process.
Effect Of Dilution On OH- Ion Concentration Of A Base
When a base is diluted, the concentration of OH- ions per unit
volume decreases and the solution becomes less basic.
How Strong Are The Acid Or Base Solutions
The strength of acid or base solutions depends upon the
presence of more and more numbers of H+ and OH- ions
respectively. The method to judge the strength of an acid or a
base is as follows: (i) By using universal indicator which is a mixture of several
indicators. It shows different colours at different
concentrations of H ions in the solution.
(ii) By using pH scale where ‘p’ stands for ‘potenz’ in German
meaning power.
pH Scale
A scale for measuring hydrogen ion concentration is called pH
scale. On the scale we can measure pH from zero (very acidic)
to 14 (very basic). Higher is the H+ ion concentration, lower is
the pH value. The pH of a neutral solution is 7. Value less than
7 represents that the solution is acidic, values more than 7
represents that the solution is basic.
pH = - log [H+]
The pH of a solution is defined as the negative log of its
hydrogen ion concentration.
Dilution Of Concentrated Acid
Mixing of an acid with water is called dilution of an acid. It is
an exothermic process.
To dilute an acid it is added to water slowly and is continuously
stirred. It is because dilution of concentrated acid is a highly
exothermic reaction. If water will be added to acid the heat
produced will be so large that the solution may splash out or
the glass beaker may break due to excessive heat. Hence for
dilution, the acid is always added to water and not water into
acid.
Effect Of Dilution On H+ Ion Concentration Of An Acid
When an acid is diluted, the concentration of H+ ions per unit
volume decreases and the solution becomes less acidic.
Chemical Nature Of Base
Bases are oxides and hydroxides of metals. A base is a
substance which when dissolved in water gives hydroxide ions
(OH-) in the solution. Bases which are soluble in water are
called alkalis.
All alkalis are bases whereas all bases are not alkalis.
Because all bases do not dissolve in water therefore they do
not release OH- ions in their aqueous solutions.
Examples Of Some Bases
CaO, MgO, CuO, NaOH, Mg(OH) 2 , Ca(OH) 2 , NH 4 OH.
Strong And Weak Acids And Bases
Strength of an acid or a base depends upon the number of
ions produced in the solution. Greater is the dissociation i.e.,
greater is the amount of H+ or OH- ions produced in the
solution, stronger is the acid or base.
Strong Acids
Acids which completely dissociate into ions, are called strong
acids. For example HCl, H 2 SO 4 and HNO 3 are strong acids
HCl + H 2 O → H+ + ClHNO 3 + H 2 O → H+ + NO 3 -
H 2 SO 4 + H 2 O → 2 H+ + SO 4 2The dissociation of strong acids is represented by putting
single arrow ( → ) towards the ions produced.
Weak Acids
Acids which partially dissociate into ions in their aqueous
solutions are called weak acids. For example Acetic acid,
(CH 3 COOH), Carbonic acid (H 2 CO 3 ), Phosphoric acid (H 3 PO 4 )
etc. are called weak acids.
CH 3 COOH
H 2 CO 3
CH 3 COO- + H+
2H+ + CO 3 2-
3H+ + PO 4 3H 3 PO 4
The dissociation of weak acids is represented by putting a
double arrow (
) one pointing towards the ions
produced and the other pointing towards the undissociated
ions.
Strong Bases
Bases which completely dissociate into their ions are called
strong bases. For example NaOH, KOH.
KOH → K+ + OHNaOH → Na+ + OHWeak Bases
The bases which partially dissociate into their ions are called
weak bases. For example Ca(OH) 2 , NH 4 OH.
Ca(OH) 2
NH 4 OH
Ca2+ + 2OH4+
NH
-
+ OH
Importance Of pH In Every Day Life
Are Plants And Animals pH Sensitive?
Our body works within pH range of 7.0 to 7.8. Living
organisms can survive in only a narrow range of pH change.
When pH of rain water is less than 5.6, it is called acid rain.
When this acid rain mixes with river water, it makes the water
acidic due to which the survival of the aquatic animals
becomes difficult.
pH Of Soil
Plants require a specific pH range for their healthy growth. To
maintain their good health the ph of soil should be maintained
according to the plant’s requirements.
pH In Our Digestive System
As our stomach secretes hydrochloric acid, the ph of our
stomach is acidic. This acid helps in the proper digestion of
food without harming the stomach. During indigestion the
stomach produces too much acid and it causes pain and
irritation. To get rid of the pain the people use bases called
antacids. These antacids neutralize the excess acids.
pH Change As The Cause Of Tooth Decay
Tooth decay starts when the ph of the mouth is lower than
5.5. Tooth enamel made up of calcium phosphate is the
hardest substance in the body. It does not dissolve in water,
but it is corroded in acidic medium that is pH below 5.5.
Bacteria present in the mouth produce acids by degradation of
sugar and food particles remaining in the mouth after eating.
The best way to prevent this is to clean the mouth after
eating. Toothpastes which are basic can also help to prevent
tooth decay.
Self Defense By Animals And Plants Through Chemical
Warfare
Bee sting leaves an acid which causes pain and irritation. Use
of a mild base like baking soda on the stung area gives relief.
Stinging hair of nettle leaves inject methanoic acid which
causes burning pain.
Salts
Salts are the ionic compounds formed by the following
methods: (i) Neutralization of acids and bases
(ii) Action of metals on acids
(iii) Action of metals on carbonates and bicarbonates
(iv) Action of metals on alkalies
Example
NaOH + HCl → NaCl + H 2 O
Zn + H 2 SO 4 → ZnSO 4 + H 2
CaCO 3 + HCl → CaCl 2 + H 2 O + CO 2
NaHCO 3 + HCl → NaCl + H 2 O + CO 2
NaOH + Zn → Na 2 ZnO 2 + H 2
pH Of Salt Solution
Depending upon the nature of the acid and the base reacting
to form the salt, the salts can be classified as follows: (i) Acidic Salts
(ii) Basic Salts
(iii) Neutral Salts
Acidic Salts
A salt of strong acid and weak base is called acidic salt.
Example
NH 4 Cl, CuSO 4 , AlCl 3 , ZnSO 4 , Ca(NO 3 ) 2
NH 4 OH + HCl → NH 4 Cl + H 2 O
Basic Salts
A salt of strong acid and a weak base is called basic salt.
Example
Na 2 CO 3 , NaHCO 3 , CH 3 COONa
NaOH + Na 2 CO 3 → Na 2 CO 3 + H 2 O
Neutral Salts
A salt of strong acid and a strong base is called neutral salt.
Example
NaCl, NaNO 3 , KCl, KNO 3
KOH + HNO 3 → KNO 3 + H 2 O
A salt of weak acid and a weak base is also called neutral salt
with pH nearly 7.
Example
CH 3 COONH 4
CH 3 COOH + NH 4 OH → CH 3 COONH 4 + H 2 O
Common Salt
Chemically common salt is sodium chloride (NaCl). Common
salt is a mixture of sodium chloride (main constituent),
magnesium chloride, potassium iodide.
Sources From Where Common Salt Is Obtained
(i) Sea Water
Sea water mostly contains sodium chloride. To extract the
salt from sea water, it is kept to evaporate in shallow
tanks. The salt obtained contains impurities of magnesium
chloride, magnesium sulphate. The salt is therefore
purified.
(ii) Rock Salt
Beds of rock salt have been formed as a result of drying
up of seas.
(iii) Inland Lakes
Large quantities of salts are obtained by the natural
evaporation of water of the inland lakes.
Cl + Cl → Cl 2
Na+ and OH- ions left in the solution combine with each other
to form sodium hydroxide.
Na+ + OH- → NaOH
The sodium hydroxide solution is formed near the cathode.
Uses Of Caustic Soda
(i) It is used in the manufacturing of soaps and detergents.
(ii) It is used for degreasing metals.
(iii) It is used in the paper industry.
(iv) It is used in the manufacturing of dyes.
(v) Used in petroleum refining.
(vi) It is used for making cotton unshrinkable.
(vii) It is used as a laboratory reagent.
Bleaching Powder
Physical Properties Of Common Salt
(i) It is a crystalline colourless solid.
(ii) It is soluble in water.
(iii) It is hygroscopic in nature due to the presence of
magnesium and calcium chloride in it.
(iv) It has a melting point of 8200C.
Note
Common salt is an important raw material for the
manufacturing of a number of other chemicals such as sodium
chloride, hydrochloric acid, sodium hydroxide, washing soda,
baking soda, bleaching powder and many others.
Chemical Name: - Calcium Oxychloride
Chemical Formula: - CaOCl 2 or Ca(OCl)Cl
Manufacturing Process: - Hasenclever Plant
Manufacture Of Bleaching Powder
Bleaching powder is manufactured by passing chlorine gas
over dry slaked lime.
Ca(OH)2
+
Cl2
→
CaOCl2
+
H2O
Slaked
Chlorine
Bleaching
Water
Lime
Gas
Powder
The manufacture of bleaching powder is carried out by two
methods.
1. Hasenclever Method
2. Bachmann’s Method
Caustic Soda
Hasenclever Method
Chemical Name: - Sodium Hydroxide
Chemical Formula : - NaOH
Manufacturing Process : - Chlor Alkali Process
Hasenclever plant consists of a number of cast iron cylinders
each provided with a rotating shaft fitted with blades and
arranged horizontally one above the other.
Process
Caustic soda is manufactured by the electrolysis of an aqueous
solution of sodium chloride called brine.
Steps For The Manufacturing
1. Slaked Lime is introduced through the hopper at the top.
2. Chlorine gas is introduced from the lower most cylinder.
3. The slaked lime is pushed onwards by the rotating shaft
until it falls into the next lower cylinder.
4. The down going lime and upcoming chlorine come in
contact with each other and the reaction take place. By
the time slaked lime reaches the lowest cylinder it has
been completely saturated with chlorine gas and is
converted into bleaching powder. The bleaching powder is
collected in a vessel placed underneath by an outlet in the
lowest cylinder. The waste gases escape through an
outlet at the top.
Physical Properties
In aqueous solution, sodium chloride dissociates
NaCl (aq) → Na+ + ClWater also dissociates to a small extent
H 2 O → H+ + OHAt Cathode the following reaction takes place
H+ + e- → H
H + H → H 2
At Anode the following reaction takes place
Cl- → Cl + e-
1.
2.
3.
4.
It is yellowish white in colour.
It is a powdered solid.
It strongly smells of chlorine.
It is soluble in cold water. The small insoluble portion is
always left behind as the lime present in it.
Chemical Properties
1.
Reaction With Carbon Dioxide
When exposed to air bleaching powder decomposes
gradually due to its reaction with carbon dioxide present
in the atmosphere giving off chlorine.
CaOCl2
CO2
+
→
Calcium oxychloride
Carbon dioxide
(Bleaching powder)
(From air)
CaCO3
Cl2
+
Calcium carbonate
Chlorine
Bleaching powder always smells of chlorine because the
carbon dioxide present in air decomposes it slowly to
produce chlorine gas.
2.
Reaction With Acids
(i) Reaction With Dilute Sulphuric Acid
When bleaching powder is treated with an excess of
dilute sulphuric acid, then all the chlorine present in it
is liberated.
CaOCl2
H2SO 4
+
Calcium oxychloride
(Bleaching powder)
→
Cl2
+
+
Chlorine
Gas
Calcium sulphate
Water
Reaction With Dilute Hydrochloric Acid
When bleaching powder is treated with an excess of dilute
hydrochloric acid, all the chlorine present in it is liberated.
CaOCl2
HCl
+
Calcium oxychloride
(Bleaching powder)
Calcium Chloride
6.
Cl2
+
Uses Of Bleaching Powder
5.
→
Hydrochloric acid
(Dilute)
CaCl2
2.
3.
4.
+
Chlorine Gas
H2O
Water
Bleaching powder is used for bleaching cotton and linen in
textile industry and for bleaching wood pulp in paper
industry. It is also used for bleaching clothes in laundry.
It is used for the manufacture of Chloroform (CHCl 3 )
Bleaching powder is used for making wool unshrinkable.
It is used as an oxidizing agent in many chemical
industries.
It is used for disinfecting lavatories, drainages and
ditches.
It is used as disinfectant and germicide in sterilization of
water.
Plaster Of Paris (POP)
Chemical Name: - Calcium Sulphate Hemi hydrate
1
H2O
Chemical Formula: - CaSO 4 .
2
Preparation Of Plaster Of Paris
It is prepared from Gypsum ( CaSO 4 .2H2O ) at 1000C (373 K)
in a kiln. At 1000C gypsum looses three fourth of its water of
crystallization and forms plaster of paris.
CaSO 4 .2H2O
1.
2.
It is a white powder
It can settle into hard mass.
Chemical Properties
1.
Reaction With Water
When water is added to plaster of Paris it set into a hard
mass in about half an hour due to dehydration.
CaSO 4 .
H2O
Available Chlorine
The amount of chlorine which is liberated during reaction
of bleaching powder with acid is called available chlorine.
Greater the amount of available chlorine more superior
the bleaching powder would be. A good sample of
bleaching powder contains 35 to 38 percent of available
chlorine.
1.
Physical Properties
Sulphuric acid
(Dilute)
CaSO 4
2.
Plaster Of Paris
Water
Heating of Gypsum should be controlled carefully. The
temperature should not be allowed to go beyond 1000C
because above 1000C all water of crystallization is eliminated
and anhydrous calcium sulphate called dead burnt plaster
(CaSO 4 ) is formed. It does not have the properties of plaster
of paris.
1
H2 O
2
    →
1
H2O
2
CaSO 4 .
1
H2O
2
+
1
1
H2O ↑
2
CaSO 4 .2H2O
Water
Uses Of Plaster Of Paris
1.
2.
3.
4.
5.
6.
It is used in making cast of statues, toys, models, and
decorative articles.
It is used for making fire proof materials.
It is used for making chalks for writing on the blackboard.
It is used for setting fractured bones.
It is used in dental surgery for making casts of denture.
It is used for sealing air gaps.
Baking Soda
Chemical Name: - Sodium Hydrogen Carbonate
Sodium Bicarbonate
Chemical Formula: - NaHCO 3
Or
Preparation Of Sodium Hydrogen Carbonate
In the laboratory and on a small scale baking soda is prepared
by passing carbon dioxide gas through a cold saturated
solution of sodium carbonate. Being less soluble, sodium
bicarbonate settles down as white crystals.
Na 2 CO 3 + H2 O + CO 2 → 2NaHCO 3
Sodium Bicarbonate
Manufacture Of Sodium Hydrogen Carbonate (Baking
Soda)
Raw Materials
1. Concentrated Solution Of Sodium Chloride (NaCl)
Common Salt (Brine).
2. Ammonia Gas (NH 3 )
3. Carbon Dioxide (Obtained By Heating Limestone CaCO 3 )
On large scale sodium hydrogen carbonate is obtained as an
intermediate product in the Solvay process of manufacture
of washing soda by passing carbon dioxide through brine
solution saturated with ammonia. The reaction for the
preparation of baking soda can also be written as: Carbonation Of Ammoniacle Brine
NaCl
+
NH3
Ammonia
(373 K )
Gypsum
→
Gypsum
(sets as hard mass)
The process is known as setting of plaster of Paris. It is an
exothermic reaction.
Plaster Of Paris
Sodium
chloride
Heat to 100 o C
+ 1
Ammoniacal brine
+
H2O
Water
+
CO2
Carbon
Dioxide
NaH CO3
→
NH4 Cl
+
Sodium hydrogen
Carbonate
Ammonium
Chloride
Physical Properties
1.
2.
3.
4.
Sodium Bicarbonate is a white crystalline solid and is
stable in air.
It is sparingly soluble in water.
When baking soda is heated it gives out carbon dipxide.
The solution of sodium hydrogen carbonate in water is
mildly alkaline.
1.
2.
Action Of Heat
On heating sodium hydrogen carbonate releases carbon
dioxide and water forming sodium carbonate.
Heat
2NaHCO3
 
→
Sodium hydrogen carbonate
(Baking soda)
Na2CO3
Sodium
Carbonate
2.
+
CO2
Carbon
dioxide
+
Reaction With Acids
Sodium hydrogen carbonate is decomposed on reaction
with acids and gives effervescence with the evolution of
carbon dioxide.
NaHCO3 + HCl → NaCl + H2O + CO2
Uses Of Baking Soda
1.
2.
3.
4.
5.
It is used as a mild antiseptic
It is used in foam type fire extinguisher
It is used for neutralizing stomach acidity
It is used in aerated water (Soda Water)
It is used in baking powders of sodium hydrogen
carbonate.
+
Water
CO2
Carbon
dioxide
NaH CO3
+
Sodium hydrogen
Carbonate
NH4 Cl
Ammonium
chloride
3.
Filtration
Sodium hydrogen carbonate forms a suspension in
ammonaical chloride solution so it is separated by
filtration.
4.
Calcination Of NaHCO 3
The filtered out sodium hydrogen carbonate is dried and
heated. On heating sodium hydrogen carbonate
decomposes to form sodium carbonate.
2NaHCO3
Heat
 
→
Sodium Hydrogen
carbonate
Na2CO3
CO2
H2O
+
+
Sodium carbonate
Carbon
Water
(Soda ash)
Dioxide
This process gives anhydrous sodium carbonate called
soda ash.
Occurrence
5.
Manufacture Of Sodium Carbonate Decahydrate
Recrystallization Of Sodium Carbonate (Soda Ash)
Anhydrous sodium carbonate is dissolved in water and
recrystalized to get washing soda crystals containing 10
molecules of water of crystallization.
Na2CO3
+
10H2O
Anhydrous
sodium
carbonate
(Soda ash)
Sodium Carbonate is manufactured on large scale by Solvay
Process (Ammonia – Soda Process)
Solvay Process
Ammonia
→
Chemical Name: - (Sodium Carbonate Decahydrate)
Chemical Formula: - (Na 2 CO 3 .10H 2 O)
Washing soda is sodium carbonate containing 10 molecules of
water of crystallization. Sodium carbonate which does not
contain any water of crystallization is called anhydrous sodium
carbonate or Soda Ash (Na 2 CO 3 ).
Raw Materials
1. Concentrated Solution Of Sodium Chloride (NaCl) i.e.,
Common Salt (Brine).
2. Ammonia Gas (NH 3 )
3. Carbon Dioxide (Obtained By Heating Limestone CaCO 3 )
H2O
+
Ammoniacal brine
Washing Soda
Sodium Carbonate occurs in crude form as deposits in the
lakes of many dry regions such as East Africa, Egypt, and USA.
In India sodium carbonate is found in Dehradun, Mathura,
Jaunpur, Varanasi etc. in the form of ‘reh’ and ‘sajji’. About
1.54 million tonnes of soda ash are produced in India every
year.
NH3
+
Sodium
Chloride
Water
H2O
+
Sodium
Ammonia
Water
Chloride
Carbonation Of Ammoniacle Brine Solution
The ammoniacal brine is dropped from the top of a tower
called carbonating tower or Solvay tower packed with
perforated plates. These partitions are to slow down the
down coming ammoniacal brine solution. Carbon dioxide
is introduced from the base of the tower. As the slow
down coming ammonaical brine comes down from the top
of a carbonating tower, tt reacts with upcoming Carbon
dioxide to form sodium hydrogen carbonate. Ammoniacal
brine is made to come down slowly so that the upcoming
carbon dioxide has enough time to react with it
completely.
NaCl
H2O
NH3
+
NaCl
Chemical Properties
1.
Saturation Of Brine With Ammonia
A cold and concentrated solution of Sodium Chloride
called brine is salted with ammonia to obtain ammoniacal
brine.
→
Water
This is how washing soda is obtained.
Physical Properties
1.
2.
Washing Soda is a white crystalline solid
Efflorescence
Na2CO3 .10H2O
Sodium carbonate
decahydrate
(Washing soda)
On exposure to air it looses nine molecules of water of
crystallization to form white powder of sodium carbonate
monohydrate.
Na2CO3 .10H2O
Expose to air
   →
Sodium carbonate
Decahydrate
(Washing soda)
(Efflorescence
Na2CO3 .H2O
9 H2O ↑
+
Sodium carbonate Monohydrate
Water
(White powder)
(Goes to air)
The phenomenon of losing water of crystallization partly
or completely on exposure to air is called efflorescence.
3.
Washing soda is one of the few metal carbonates which
are soluble in water. Its aqueous solution is alkaline due
to hydrolysis and formation of sodium hydroxide. The
solution of washing soda in water is alkaline which turns
red litmus to blue.
Chemical Properties
1.
Effect Of Heat
Washing soda is stable below 373 K. It looses all the
water of crystallization and form anhydrous sodium
carbonate.
Na2CO3 .10H2O
Heat
Water
Action Of Acids
It is readily decomposed with mineral acids giving
effervescence (bubbles) due to evolution of carbon
dioxide.
Na2CO3 + 2HCl
3.
+ 10H2O ↑
Anhydrous
sodium
carbonate
Sodium carbonate
decahydrate
2.
Na2CO3
 
→
→
2NaCl
+
H2O
+
CO2
Sodium Chloride
Detergent Properties
Washing soda has detergent properties because it can
remove dirt and grease from dirty clothes etc.
Uses Of Sodium Carbonate Decahydrate
1.
2.
3.
4.
5.
6.
It is used in laundry and in softening of water as washing
soda.
It is used as a laboratory reagent in qualitative analysis as
fusion mixture (a mixture of sodium carbonate and
potassium carbonate).
It is used in paper, paints, petroleum and textile industry.
It is used in the preparation of carbonates of metals.
It is used in large quantities in the manufacture of glass,
borax, soap, detergents and caustic soda.
It is used in quantitative analysis to standardize acid
solution.
Water Of Crystallization
Water of crystallization is fixed number of water molecules
present in one formula unit of a salt. These water molecules
have a very weak bonding with the salt and hence they can be
easily removed.
Are The Crystals Of Salts Really Dry?
No the crystals of salts are not really dry because they contain
water of crystallization, they only seem to be dry.
Examples Of Salts Containing Water Of Crystallization
(i) Hydrated Copper Sulphate CuSO 4 .5H 2 O
(ii) Gypsum Or Hydrated Calcium Sulphate CaSO 4 .2H 2 O
(iii) Washing Soda Or Hydrated Sodium Carbonate
Na 2 CO 3 .10H 2 O
(iv) POP Or Hydrated Calcium Sulphate CaSO 4 .1/2 H 2 O
(v) Bauxite Or Hydrated Alluminium Oxide Al 2 O 3 .2H 2 O
(vi) Magnesium Or Epsom Salt Or Hydrated magnesium
Sulphate MgSO 4 .7H 2 O
(vii) Limonite Or Hydrated Iron Oxide Fe 2 O 3 .3H 2 O
To know about the fact that the crystals of salts are not really
dry, we can heat the crystals of copper sulphate. We will see
that on heating the water of crystallization is removed and the
salt turns white. If we moisten the crystals again with water,
we will find that blue colour of the crystals reappear. It shows
that the crystals only seem to be dry they are not actually dry.