Alkali metal

Alkali Metals
Dr. Damodar Koirala
Amarsingh Model Secondary School
Pokhara, Nepal

Chemistry
Physical / Inorganic / Organic / Industrial…
Non-metal / Metal / Bio…
Metallurgy / Alkali / Alkaline Earth…
Li / Na / K /Rb / Cs/ Fr
NaOH / Na2CO3
2
Dr. Damodar Koirala koirala2059@gmail.com

Periodic table
3
Periodic table is divided into 4 blocks depending on
where last electron goes to

Periodic table
4

s-block elements
Group 1 (alkali) and Group 2 (alkaline earth)
which have ns1 and ns2 outermost electronic
configuration respectively
All reactive metals with low ionization energy
Lose outermost electron(s) readily to form 1+ ion
(alkali) or 2+ ion (alkaline earth)
Highly reactive hence never found pure in nature
5

Alkali metals
Group 1 element with outermost electronic
configuration of ns1
Sodium and potassium are abundant
Lithium, rubidium and cesium are lower
abundance
Francium is highly radioactive:
6

General characteristics
Electronic configuration
Atomic and ionic radii
Ionization energy
Physical properties
7

Electronic configuration
All alkali metals have 1 valence electron, so
ns1 outer most electronic configuration
8

Atomic and ionic radii
Def: distance from the center of the nucleus to the
boundary of the surrounding shells of electrons
Alkali metals have largest sizes in a particular period
of the periodic table
The monovalent ions (M+) are smaller than the
parent atoms (M)
The atomic and ionic radii of alkali metals increases
on moving down the group ( Li to Ce)
9

Ionization energy
Def: The amount of energy required to remove
loosely bound electron from isolated gaseous
atom
Alkali metals have low I.E (easy to remove
electron)
I.E decreases down the group : Since the
increasing size outweighs the increasing nuclear
charge
10

Physical properties
Silvery white, soft and light metal
Low density and increases down the group
Low mp and bp indicating weak metallic bonding due to only 1
valence electron
They and their salt impart characteristic color in an oxidizing flame
11
Metal Li Na K Rb Cs
Color Crimson Red Yellow Violet Violet Red Blue
nm 670.8 589.2 766.5 780.0 455.5

Extraction of sodium from NaCl :
Challenges / Overcome
Mp of NaCl is 801C. At this temperature, molten NaCl
and Na forms a metallic fog in the container which is
impossible to separate
To overcome this challenge, a mixture of NaCl and
CaCl2 is electrolyzed. The mp of the mixture is 600C ;
no metallic fog is formed at this temperature.
12

Occurrence of sodium
Do not occur in free state
Occurs as compound
NaCl: Sodium chloride as rock salt and sea water
NaNO3: Sodium nitrate, Chile salt petre, Caliche
Na2B4O7.10H2O: Borax
13

Extraction of sodium :
Downs process
On industrial scale, sodium metal is extracted
by “Down’s Process”
Down’s Process is based on the electrolysis of
fused NaCl
Na+ reduced to Na in cathode
Cl- oxidized to Cl2 in anode
14

Construction of Down’s Cell
Down’s Cell is an iron vessel line with fire bricks and
containing the mixture of the salts (NaCl and CaCl2)
The graphite anode is at the centre which rises from
the bottom of the cell
The cylindrical iron cathode surrounds the anode
The cathode and anode are separated by iron wire
gauze which keeps the products (Na and Cl2)
separate from each other
15

16
Fig: Down’s Cell
When an electric current is passed through the molten mixture
of NaCl and CaCl2, NaCl decomposes in to Na+ and Cl-
ion. Na+ ions migrate towards cathode while Cl- ions towards
the anode. The molten sodium collects in the cathode
compartment where it rises to the top and is tapped off by a
pipe. Chlorine is collected at the anode.
Steel
hood
Molten
Sodium
Chlorine
Carbon anode Iron gauze
Iron
cathode
Storage tank
for sodium
Fused NaCl
and CaCl2

Down’s Cell: Reaction
Fused NaCl contains sodium and chloride ions
At Cathode: Na+ ion migrated to cathode and reduces to Na
At Anode: Cl- ion migrates to anode and oxidizes to Cl2
Overall Reaction:
17
2NaCl 2Na+ + 2Cl-
Na+ + e- Na
2Cl- Cl2 + 2e-
2NaCl 2Na + Cl2

Action of sodium with
Oxygen
Water
Acids
Nonmetals
Ammonia
18

Na with O2
Sodium burns in air with golden yellow
flame producing the mixture of its normal
oxide and peroxide
19

Na with H2O
Sodium reacts readily with water forming
sodium hydroxide and hydrogen gas. The
reaction is highly exothermic so that
hydrogen at once catches fire
20

Na with acids
21

Na with non-metals
Reacts with H2 to produce sodium hydride
22
Reacts with Halogens to produce respective
halides

Na with ammonia
Dissolves in liquid ammonia producing the
deep blue coloration.
23
The blue color of the solution is due to the
ammoniated electron which absorbs energy
in the visible region of light.

Uses of sodium
In sodium vapour lamp which gives yellow
light and in photoelectric cell
In nuclear reactor as a heat exchanger
In production of artificial rubber, dyes, drugs
and perfumes
24

Sodium hydroxide
Common name: Caustic soda
Molecular formula : NaOH
1 mole of NaOH has 40 g NaOH
1 mole NaOH contain 23g Na, 16g oxygen, 1g hydrogen
1mole NaOH contain 1 mole Na atom, 1 mole oxygen atom,
and 1 mole hydrogen atom
1 mole NaOH contains 0.5 mole oxygen molecules and 0.5
moles hydrogen molecules
25

NaOH: Manufacturing
Demand of NaOH is very high
Primarily manufactured by electrolysis of
NaCl solution
Mercury Cathode is used
Castner - Kellner’s process
Kellner-Solvay process
26

27
Graphite
electrode
Eccentric
Wheel
Mercury
Graphite
electrode
Caustic soda solution
Iron cathode
Slate partitions brine
Cl2
H2 (-)
(+) (+)
Fig: Castner-Kellner cell for manufacturing of NaOH
Cl2
- - - - - - - -
+ + + + + + +

It consists mercury cathode cell which is a large rectangular
iron vessel divided into three compartments by a non-porous
slate partition. The partition do not touch the bottom of the
cell.
The two outer compartments contain the concentrated brine
solution with graphite anode. The central compartment
contains dilute sodium hydroxide solution with iron cathode.
The bottom of the cell contains the layer of mercury, which
serves as cathode in outer compartments and as anode in
central compartment. The mercury is allowed to move from
one compartment to another by means of an eccentric wheels.
28

On passing electricity:
At outer compartments, sodium ions are discharged at
mercury cathode and form amalgam.
Thus formed amalgam passes into central compartment due
to rocking motion and reacts with water to produce NaOH
solution and H2 gas. From this reaction, Hg is regenerated .
Solid NaOH is obtained by evaporating the solution from
central compartment and then it is cast to sticks to get its
pellets
29

Reaction (Side compartment)
At cathode
At anode
Reaction (Central compartment)
At anode
At cathode
30
Na+ + e- + Hg NaHg
NaHg Na+ + Hg + e-
Na+ + e- Na
2Cl- Cl2(g) + 2e-
2Na + 2H2O 2NaOH + H2

31
Fig: Kellner-Solvay cell for manufacturing of NaOH
Cl2
(+) Anode Brine in
Mercury in
Amalgam out
Spent
brine
(-) Cathode

Kellner-Solvay cell has replaced Castner-Kellner cell to some extent
This cell has single compartment without any partition.
The cell consist of a big rectangular from through, called
electrolyzer, at the basis of which there is a thin layer of mercury
flowing from one end to the other.
The layer of mercury acts as cathode.
A concentrated brine solution flows slowly through the cell in the
same direction as Hg flows and is maintained at a constant level.
The graphite anodes are suspended into the brine.
32

33
On passing electricity:
Cl- oxidizes to Cl2 in an anode
Sodium ions are reduced at the mercury cathode and form
sodium amalgam
Sodium amalgam flows into iron tank called decomposer, where
NaHg is decomposed by calculated amount of water to produce
caustic soda and regenerating mercury.
Solid NaOH is obtained by evaporating the solution from
central compartment and then it is cast to sticks to get its pellets.

Reaction
At cathode
At anode
At decomposer
34
Na+ + e- + Hg NaHg
2NaHg + 2H2O 2NaOH + 2Hg + H2
2Cl- Cl2(g) + 2e-

NaOH by Diaphragm Cell
Principle
Electrolysis of brine solution is carried out between graphite anode
and steel mesh cathode
Cell consist of two compartment separated by a permeable asbestos
diaphragm. Ions can pass through diaphragm but gas molecules
cannot.
Anodic compartment is supplied with brine solution and cathodic
compartment with water
During electrolysis, Cl2 is discharged from anode and H2 from
cathode
35

36
Hydrogen
gas
Chlorine
gas
Graphite
anode
Steel
cathode
Brine containing
NaOH
Brine
Brine
Brine
Brine
Asbestos diaphragm
Fig: Manufacturing of NaOH by diaphragm cell

Reaction
At cathode
At anode
Na+ travel through the diaphragm and combine
with OH- to form NaOH
37
2H2O + e- H2(g) + 2OH-
Na+ + OH- NaOH
2Cl- Cl2(g) + 2e-

NaOH: Physical properties
White deliquescent solid
Soluble in water and alcohol
Solution is soapy to touch
Mp: 318C
Corrosive action on skin
38

Action of NaOH with
Carbon monoxide
Precipitation reaction
39

NaOH with CO
NaOH reacts with Carbon monoxide to
produce sodium formate.
40
Reaction takes place on high pressure,
120-130°C and in presence of catalyst.

NaOH precipitation reaction
Certain metal hydroxide precipitate:
41
In some cases, ppt dissolves in excess NaOH
FeCl3 + 3NaOH Fe(OH)3 + 3NaCl
Brown ppt
ZnSO4 + 2NaOH Zn(OH)2 + Na2SO4
White ppt
Zn(OH)2 + 2NaOH Na2ZnO2 + 2H2O
Sodium zincate
Al(OH)3 + NaOH NaAlO2 + 2H2O
Sodium meta aluminate

NaOH uses
In refining petroleum products and vegetable
In manufacturing of soap, paper, cellulose, artificial
silk
For the extraction of sodium metal by Castner’s
process
For testing wool as NaOH dissolves pure wool
giving a gelatinous mass
42

Sodium carbonate
43
Common name: Washing soda (Na2CO3 .10 H2O)
1 mole of Na2CO3 has 106 g Na2CO3
1 mole Na2CO3 contain 46g Na, 12g carbon, 48g
oxygen
1mole Na2CO3 contain 2 mole Na atom, 1 mole
carbon atom and 3 mole oxygen atom
1 mole Na2CO3 contains 1.5 mole oxygen molecules

Na2CO3 Manufacturing
44
Primarily manufactured by Solvay’s ammonia
process, which is also called ammonia soda
process
Raw materials:
Brine, NaCl
Lime Stone, CaCO3
Ammonia, NH3

Solvay Process: Principle
45
Brine solution is saturated with ammonia and excess carbon
dioxide gas is passed through it
Sodium bicarbonate is produced
Sodium bicarbonate is removed by filtration and then ignited to
get sodium carbonate
Thus formed sodium carbonate solution is crystalline to get the
washing soda crystals
NH3 + H2O + CO2 NH4HCO3
NaCl + NH4HCO3 NaHCO3 + NH4Cl
2NaHCO3 Na2CO3 + H2O + CO2

46
Fig: Solvay process for manufacturing of Na2CO3
NH3 + a little CO2
Brine
Filter
Filter
Water
Steam
NH4Cl + a little NH4HCO3
NaHCO3 (For ignition)
Ca(OH)2
Tower
CaCl2
CO2
Ammonia
Absorber
Ammonia
Recovery
tower
Lime
Klin
Carbonation
tower
Ammoniacal
brine
CaO

1. Saturation of brine with
ammonia
47
Brine is pumped into the ammonia absorber.
Ammonia mixed with a little carbondioxide from the
ammonia generating tower enters the ammonia absorbing
tower and saturates the in coming brine.
Impurities of calcium or magnesium salts in brine are
precipitated as hydroxides or carbonates.
NH3 + CO2 + H2O (NH4)2CO3
CaCl2 + (NH4)2CO3 CaCO3ppt + 2NH4Cl
NH3 + H2O NH4OH
MgSO4 + 2NH4OH Mg(OH)2ppt + (NH4)2SO4

2. Carbonation
48
The ammonical brine solution is filtered and allowed to
enter carbonating tower from its top
The down coming ammonical brine solution meets an
upward stream of CO2 gas coming from the lime klin.
Small crystals of sodium bicarbonate are formed.
CaCO3 CaO + CO2
NH4HCO3 + NaCl NaHCO3 + NH4Cl
NH3 + H2O + CO2 NH4HCO3

3. Filtration
49
The thick milky liquid from carbonating
tower is filtered by rotary vacuum filter
The solid sodium bicarbonate left on the filter
cloth is scrapped periodically
The filtrate and the mother liquor are
pumped to the top of the ammonia recovery
tower

4. Recovery of ammonia
50
The filtrate containing ammonium chloride with a little
ammonium bicarbonate flows down the ammonia
recovery tower while slaked lime is admitted into the
tower and steam is admitted from the bottom of tower.
Ammonium bicarbonate decomposes due to heat and
ammonium chloride combine with the lime.
NH4HCO3 NH3 + H2O + CO2
Ca(OH)2 + 2NH4Cl 2NH3 + CaCl2 + 2H2O

5. Calcination
51
Sodium bicarbonate obtained from filtration is
calcined to get sodium carbonate
Carbondioxide obtained from this reaction is reused in
carbonation tower.
Crystallization of sodium carbonate solution is carried
out to get sodium carbonate crystals.
2NaHCO3 Na2CO3 + H2O + CO2

Advantages of Solvay process
52
The materials are cheap and the product
obtained is of high purity

Action of Na2CO3 with
Carbondioxide
Sulphur dioxide
Water
Precipitation reaction
53

Na2CO3 with CO2
Sodium bicarbonate is formed when CO2 is
passed into aq. Na2CO3
54
Na2CO3 + CO2 + H2O 2NaHCO3
(aq)

Na2CO3 with SO2
55
Sodium sulphite is formed when SO2 is
passed into aq. Na2CO3
Sodium bisulphite is formed when SO2 is
passed into Na2CO3
Na2CO3 + SO2 + H2O 2NaHSO3
(aq)
Na2CO3 + SO2 2Na2SO3 + CO2

Na2CO3 with H2O
It produces NaOH and H2CO3, the solution is
alkaline
56
Hence, the aqueous Na2CO3 turns red litmus
to blue and phenolphthalein to pink
Na2CO3 + 2H2O 2NaOH + H2CO3
Strong base Weak acid

Na2CO3 precipitation reactions
It precipitate the carbonates of non-alkali
metals from their salt solution
57
CaCl2 + Na2CO3 CaCO3 + 2NaCl
ppt
BaCl2 + Na2CO3 BaCO3 + 2NaCl
ppt
2AgNO3 + Na2CO3 Ag2CO3 + 2NaNO3
Ppt

Uses Na2CO3
As washing soda for washing clothes
In softening of water
In manufacturing of glass, borax and caustic
soda
As a household cleansing agent
58

Flow Chart
Shows steps as box in sequential order of the processes.
59

60
Flow Chart

NaCl
Na+
+
Cl-
2Cl-
Cl
2
+
2e-
2H
2
O
+
2e-
H
2
+
2OH-
Brine
precipitation
Brine
heating
Brine
purification
Salt
Dissolving
Salt
Water
Evaporation
Liquification
Compression
Drying
Cooling
Step 1: Brine Production
Step 2: Brine
Electrolysis Step 3: Cl2 and H2 processing
DC
AC
Concentration
Cooling
Storage
Step 4: Caustic evaporation
Caustic soda
(NaOH)
Cooling
Depleted
Brine
Cl2
H2
Fig: Flow chart for
manufacturing of NaOH
by Diaphragm cell
NaOH

Lime stone
(CaCO3)
Lime kiln tower
CaCO3 CaO + CO2
Lime slaker
CaO + H2O Ca(OH)2
Carbonation tower
NH3 + CO2 + H2O NH4HCO3
NH4HCO3 + NaCl NaHCO3 + NH4Cl
Filter
Intermediate Product
(NaHCO3)
Product (Na2CO3)
Ammonia recovery tower
2NH4Cl + Ca(OH)2.
CaCl2 + 2NH3 + 2H2O
By product
(CaCl2)
Brine
NaCl(aq)
Ammonia
NH3(g)
Ammonia absorber tower
NaCl, NH3, H2O
300 C (ignition)
NH3
NH4Cl
Ca(OH)2
CaO
CO2
H2O
Fig: Flow chart for
manufacturing of Na2CO3
by Solvay process

Alkali metal

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