Borax
👉It is the most important compound of boron.
👉It is a white crystalline solid of formula
Na2B4O7.10H2O.
👉In fact it contains the
tetranuclear units [B₄O₅(OH)₄]²⁻ and correct
formula; therefore, is Na2[B4O5 (OH)4].8H2O.
👉
👉On heating, borax first loses water
molecules and swells up. On further heating it
turns into a transparent liquid, which solidifies
into glass like material known as borax
bead.
👉
👉The metaborates of many transition metals
have characteristic colours and, therefore,
borax bead test can be used to identify them
in the laboratory.
👉For example, when borax is
heated in a Bunsen burner flame with CoO on
a loop of platinum wire, a blue coloured
Co(BO2)2 bead is formed.
Cleansing Agents
👉Two types of detergents
are used as cleansing agents. These are soaps and synthetic detergents.
These improve cleansing properties of water. These help in removal of
fats which bind other materials to the fabric or skin.
👉Soaps used for cleaning
purpose are sodium or potassium salts of long chain fatty acids, e.g.,
stearic, oleic and palmitic acids. Soaps containing sodium salts are
formed by heating fat (i.e., glyceryl ester of fatty acid) with aqueous
sodium hydroxide solution. This reaction is known as saponification.
👉Types of soaps
👉Toilet soaps are prepared by using better grades of fats and oils
and care is taken to remove excess alkali. Colour and perfumes are
added to make these more attractive.
👉Soaps that float in water are made by beating tiny air bubbles
before their hardening.
👉Transparent soaps are made by dissolving the
soap in ethanol and then evaporating the excess solvent.
👉In medicated soaps, substances of medicinal value are added. In
some soaps, deodorants are added.
👉Shaving soaps contain glycerol to
prevent rapid drying. A gum called, rosin is added while making them.
It forms sodium rosinate which lathers well.
👉Laundry soaps contain
fillers like sodium rosinate, sodium silicate, borax and sodium carbonate.
Sodium Carbonate (Washing Soda),
Na2CO3·10H2O
👉Sodium carbonate is generally prepared by
Solvay Process
👉In this process, advantage is
taken of the low solubility of sodium
hydrogencarbonate whereby it gets
precipitated in the reaction of sodium chloride
with ammonium hydrogencarbonate.
👉The
latter is prepared by passing CO2 to a
concentrated solution of sodium chloride
saturated with ammonia, where ammonium
carbonate followed by ammonium
hydrogencarbonate are formed. The equations
for the complete process may be written as :
👉
👉Sodium hydrogencarbonate crystal
separates. These are heated to give sodium
carbonate.
👉In this process NH3 is recovered when the
solution containing NH4Cl is treated with
Ca(OH)2. Calcium chloride is obtained as a
by-product.
👉It may be mentioned here that Solvay
process cannot be extended to the
manufacture of potassium carbonate because
potassium hydrogencarbonate is too soluble
to be precipitated by the addition of
ammonium hydrogencarbonate to a saturated
solution of potassium chloride.
👉Properties : Sodium carbonate is a white
crystalline solid which exists as a decahydrate,
Na2CO3·10H2O. This is also called washing
soda. It is readily soluble in water. On heating,
the decahydrate loses its water of crystallisation
to form monohydrate. Above 373K, the
monohydrate becomes completely anhydrous
and changes to a white powder called soda ash.
👉Carbonate part of sodium carbonate gets
hydrolysed by water to form an alkaline
solution.
👉Uses:
(i) It is used in water softening, laundering
and cleaning.
(ii) It is used in the manufacture of glass,
soap, borax and caustic soda.
(iii) It is used in paper, paints and textile
industries.
(iv) It is an important laboratory reagent both
in qualitative and quantitative analysis.
GROUP 13 ELEMENTS: THE BORON FAMILY
👉This group elements show a wide variation in
properties.
👉Boron is a typical non-metal,
aluminium is a metal but shows many
chemical similarities to boron, and gallium,
indium, thallium and nihonium are almost
exclusively metallic in character.
👉Boron is a fairly rare element, mainly
occurs as orthoboric acid, (H3BO3), borax,
Na2B4O7·10H2O, and kernite, Na2B4O7·4H2O.
👉In India borax occurs in Puga Valley (Ladakh)
and Sambhar Lake (Rajasthan).
👉The
abundance of boron in earth crust is less than
0.0001% by mass. There are two isotopic
forms of boron 10B (19%) and 11B (81%).
👉Aluminium is the most abundant metal and
the third most abundant element in the earth’s
crust (8.3% by mass) after oxygen (45.5%) and
Si (27.7%).
👉Bauxite, Al2O3. 2H2O and cryolite,
Na3AlF6 are the important minerals of
aluminium.
👉In India it is found as mica in
Madhya Pradesh, Karnataka, Orissa and
Jammu.
👉Gallium, indium and thallium are less
abundant elements in nature. Nihonium has
symbol Nh, atomic number 113.
USES OF BORON AND ALUMINIUM
AND THEIR COMPOUNDS
👉Boron being extremely hard refractory solid of
high melting point, low density and very low
electrical conductivity, finds many
applications.
👉Boron fibres are used in making
bullet-proof vest and light composite material
for aircraft.
👉The boron-10 (10B) isotope has high
ability to absorb neutrons and, therefore,
metal borides are used in nuclear industry as
protective shields and control rods.
👉The main
industrial application of borax and boric acid
is in the manufacture of heat resistant glasses
(e.g., Pyrex), glass-wool and fibreglass
👉Borax
is also used as a flux for soldering metals, for
heat, scratch and stain resistant glazed coating
to earthenwares and as constituent of
medicinal soaps.
👉An aqueous solution of orthoboric acid is generally used as a mild
antiseptic.
👉Aluminium is a bright silvery-white metal,
with high tensile strength. It has a high
electrical and thermal conductivity. On a
weight-to-weight basis, the electrical
conductivity of aluminium is twice that of
copper. Aluminium is used extensively in
industry and everyday life. It forms alloys with
Cu, Mn, Mg, Si and Zn. Aluminium and its
alloys can be given shapes of pipe, tubes,
rods, wires, plates or foils and, therefore, find
uses in packing, utensil making,
construction, aeroplane and transportation
industry. The use of aluminium and its
compounds for domestic purposes is now
reduced considerably because of their toxic
nature.
👉What happens when(a) Borax is heated strongly,(b) Boric acid is added to water,(c) Aluminium is treated with dilute NaOH,(d) BF3 is reacted with ammonia ?
👉An aqueous solution of borax is(a) neutral (b) amphoteric(c) basic (d) acidic
