Here we have published the 12th class chemistry chapter 3 Group IIIA and IVA Elements important short questions and answers.
Ans: The borate glazes are preferred over the silicate glazes because the borate glasses are
more fusible and possess a higher coefficient of expansion than the borate glass.
Q2 what is vicious/vitreous silica? Give two uses.
Ans: When the crystalline silica is heated to sufficiently high temperature it melts to give
the viscous liquid having a random structure which on cooling does not readily crystallize
and become rigid without having undergone the orientation into regular crystal pattern is
is called viscous/vitreous silica.
Q3 Four uses of Sodium Silicate.
Ans: It is used as filler for soap in soap industry
¡t is used in textile as fireproof
It is used as furniture polish
It is used in calico printing
Q4 Give reaction of Al with nitric acid.
Ans: Aluminum does not react with any concentration of NHO3, probably because of
formation o a protective layer of aluminum oxide. The acid is said to render the aluminum
passive that is why the nitric acid is transported in the aluminum container.
Q5: Give the equation of the reaction of Al with conc. ijSO4 and NaOH.
Ans: Muminum is amphoteric is nature as it dissolves in both acids and base with liberation
of Hydrogen gas. Al does not react with dil H2S04 however it is oxidized by hot conc. H2S04
to displace the H2
ZA1+6H2S04 > Al2(SO)3 + 6H20 + 3S02
Aluminium dissolves in NaOH to sodium aluminate to Hydrogen has
ZA1-i-2NaOH+6H20 > 2NaAI(OH)4 + 3H2
Q6 Boron differs from its family members. Discus.
Boron is the only element of the IIIA group which is non-metallic in nature.
It is the only element with less than four electrons in valence shell which is non-metallic.
Boron uses it’s all the 4 electrons in bond formation so its oxidation state is either +3 or -3.
It gives molecular addition compounds.
Boron doesn’t form ionic compounds with sulphate, nitrate as it does not form the stable cation.
Q7: Write for any uses ofAluniinum?
Because tensile strength it is used in making the air crafts ships and cars.
Being non-toxic in nature it is used for making food and brewing equipment and in packing.
Being non-magnetic if is used in navigational instruments.
Aluminum foils are used fo jam radar.
Q8 Define inert pair effect?
Ans: The ability of s-electron of valence shell of lower members of IV A group fo remain
inert (not involved) in bonding is called inner pair effect. Inert pair effect is mostly shown
by the 15-1 7f h group element s. The reason for this is the inertness of the inner s-electrons
due to poor shielding.
Q9Aluniinum not found in free nature, Comment the statement.
Ans: Due to larger atomic and lower ionization energy, Al readily losses its valence electron
and form the compound that is il not found in Free State.
Q8 Outline the four uses of borax and H3B03
Ans: a) it’s used to prepare the borax glass which is heat resistant.
b) it is used in softening of water.
c) it is used in a metallurgical operation
Uses of Orthoboric acid
a) it is used in pottery as a glaze
b) It is also used in candle industry for stiffening of wicks
c) Boric acid is used in medicines as antiseptic
Q9 Give the names and composition of different boric acids.
Ortho acid H3B03 MetaBoric acid HBO3
Tetraboric acid H2B407 pyroboric acid H6B409
Ql0 State the procedure by which stoneware is made less porous.
Am Stoneware usually glazed to give it a less porous surface by throwing salt upon the
articles while they are hot. This treatment produces sodium aluminate and sodium
aluminum silicate which melt readily and cover the entire surface. When the articles cool,
the covering solidifies, producing compact smooth waterproof surface.
Q11 Aluminum sheets are said to be corrosion free?Comment?
When a piece of Aluminum sheet is exposed to moist air it acquires a thin continuous
coating of Aluminum oxide which prevents further attack on the metal by atmospheric
oxygen and water under normal conditions. Because of this Aluminum sheets are said to be
corrosion free.
Q12 Borax serves as water softening agent.
Ans: The hardness of water is due to presences of Carbonates and Bicarbonates of Ca and Mg. When borax is added to hard water, it replaces the Ca2 and Mg2 ions by Na’ ions.
The resulting Mg borate and Ca Borate sell le down and water becomes soft.
Ql3 H3B03 is monobasic acid..?
Ans: Orthoboric acid is a weak acid and ionizes to veiçy small extent mainly monobasic
acid show by the equation
H3B03+H20 > IB(OH)J’ +H
Ql4 What is the formula unit Silicon Dioxide?
Ans: The formula unit of silicon dioxide is Si02.
Q15 what are Silicones? Give two uses?
Ans: Silicones of O-Si-O chain in which the remaining bonding position of each silicon is
occupied by organic groups like methyl or ethyl. The methyl silicon can be prepared.
Depending upon the length of the chains and degree of cross-linkages between chains
silicones may be liquid or rubber-like materials. They are used as lubricants, Gasket and for
waterproofing of fabrics.
Q16 what are semi-conductors? Give examples Give two uses.
Ans: These are substances have different resistances to the passage of current and
a compound like lead conditions
Semiconductors include elements like Germanium, Selenium, and silicon and
compounds like lead sulphide, silicon carbide, cadmium carbide, lead telluride gallium
arsenide and indium antimonite.
They are used in photoelectric cells and solar batteries
they are used in the radio-television, computer, and calculator.
Q17: CO2isgaswhileSiO2issolid.
Am: CO2 exits tiny individual molecule as being smaller in size it accommodates only two
oxygen atom hence found in the gaseous state whereas Silicon being larger in size can
accommodate four oxygen atoms simultaneously forming the three-dimensional network
and hence found in solid state
Chapter 03
Ql Borate glazes are preferred over the silicate glazes.Ans: The borate glazes are preferred over the silicate glazes because the borate glasses are
more fusible and possess a higher coefficient of expansion than the borate glass.
Q2 what is vicious/vitreous silica? Give two uses.
Ans: When the crystalline silica is heated to sufficiently high temperature it melts to give
the viscous liquid having a random structure which on cooling does not readily crystallize
and become rigid without having undergone the orientation into regular crystal pattern is
is called viscous/vitreous silica.
Q3 Four uses of Sodium Silicate.
Ans: It is used as filler for soap in soap industry
¡t is used in textile as fireproof
It is used as furniture polish
It is used in calico printing
Q4 Give reaction of Al with nitric acid.
Ans: Aluminum does not react with any concentration of NHO3, probably because of
formation o a protective layer of aluminum oxide. The acid is said to render the aluminum
passive that is why the nitric acid is transported in the aluminum container.
Q5: Give the equation of the reaction of Al with conc. ijSO4 and NaOH.
Ans: Muminum is amphoteric is nature as it dissolves in both acids and base with liberation
of Hydrogen gas. Al does not react with dil H2S04 however it is oxidized by hot conc. H2S04
to displace the H2
ZA1+6H2S04 > Al2(SO)3 + 6H20 + 3S02
Aluminium dissolves in NaOH to sodium aluminate to Hydrogen has
ZA1-i-2NaOH+6H20 > 2NaAI(OH)4 + 3H2
Q6 Boron differs from its family members. Discus.
Boron is the only element of the IIIA group which is non-metallic in nature.
It is the only element with less than four electrons in valence shell which is non-metallic.
Boron uses it’s all the 4 electrons in bond formation so its oxidation state is either +3 or -3.
It gives molecular addition compounds.
Boron doesn’t form ionic compounds with sulphate, nitrate as it does not form the stable cation.
Q7: Write for any uses ofAluniinum?
Because tensile strength it is used in making the air crafts ships and cars.
Being non-toxic in nature it is used for making food and brewing equipment and in packing.
Being non-magnetic if is used in navigational instruments.
Aluminum foils are used fo jam radar.
Q8 Define inert pair effect?
Ans: The ability of s-electron of valence shell of lower members of IV A group fo remain
inert (not involved) in bonding is called inner pair effect. Inert pair effect is mostly shown
by the 15-1 7f h group element s. The reason for this is the inertness of the inner s-electrons
due to poor shielding.
Q9Aluniinum not found in free nature, Comment the statement.
Ans: Due to larger atomic and lower ionization energy, Al readily losses its valence electron
and form the compound that is il not found in Free State.
Q8 Outline the four uses of borax and H3B03
Ans: a) it’s used to prepare the borax glass which is heat resistant.
b) it is used in softening of water.
c) it is used in a metallurgical operation
Uses of Orthoboric acid
a) it is used in pottery as a glaze
b) It is also used in candle industry for stiffening of wicks
c) Boric acid is used in medicines as antiseptic
Q9 Give the names and composition of different boric acids.
Ortho acid H3B03 MetaBoric acid HBO3
Tetraboric acid H2B407 pyroboric acid H6B409
Ql0 State the procedure by which stoneware is made less porous.
Am Stoneware usually glazed to give it a less porous surface by throwing salt upon the
articles while they are hot. This treatment produces sodium aluminate and sodium
aluminum silicate which melt readily and cover the entire surface. When the articles cool,
the covering solidifies, producing compact smooth waterproof surface.
Q11 Aluminum sheets are said to be corrosion free?Comment?
When a piece of Aluminum sheet is exposed to moist air it acquires a thin continuous
coating of Aluminum oxide which prevents further attack on the metal by atmospheric
oxygen and water under normal conditions. Because of this Aluminum sheets are said to be
corrosion free.
Q12 Borax serves as water softening agent.
Ans: The hardness of water is due to presences of Carbonates and Bicarbonates of Ca and Mg. When borax is added to hard water, it replaces the Ca2 and Mg2 ions by Na’ ions.
The resulting Mg borate and Ca Borate sell le down and water becomes soft.
Ql3 H3B03 is monobasic acid..?
Ans: Orthoboric acid is a weak acid and ionizes to veiçy small extent mainly monobasic
acid show by the equation
H3B03+H20 > IB(OH)J’ +H
Ql4 What is the formula unit Silicon Dioxide?
Ans: The formula unit of silicon dioxide is Si02.
Q15 what are Silicones? Give two uses?
Ans: Silicones of O-Si-O chain in which the remaining bonding position of each silicon is
occupied by organic groups like methyl or ethyl. The methyl silicon can be prepared.
Depending upon the length of the chains and degree of cross-linkages between chains
silicones may be liquid or rubber-like materials. They are used as lubricants, Gasket and for
waterproofing of fabrics.
Q16 what are semi-conductors? Give examples Give two uses.
Ans: These are substances have different resistances to the passage of current and
a compound like lead conditions
Semiconductors include elements like Germanium, Selenium, and silicon and
compounds like lead sulphide, silicon carbide, cadmium carbide, lead telluride gallium
arsenide and indium antimonite.
They are used in photoelectric cells and solar batteries
they are used in the radio-television, computer, and calculator.
Q17: CO2isgaswhileSiO2issolid.
Am: CO2 exits tiny individual molecule as being smaller in size it accommodates only two
oxygen atom hence found in the gaseous state whereas Silicon being larger in size can
accommodate four oxygen atoms simultaneously forming the three-dimensional network
and hence found in solid state
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