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12th Class
12th Class Punjab
Chemistry
Chemistry Short Question
Group Iiia And Group Iva Elements Short Questions Preparation

Chapter 3 Group Iiia And Group Iva Elements Chemistry 12th Class Punjab Short Questions

Question No. 1 - Aqueous solution of borax is alkaline in nature. Justify the statement.

Answer No. 1 - Aqueous solution is alkaline in nature due to hydrolysis.
Na2B4O7+ 7H2O------->2NaOH +4H3BO3
Borax Strong Alkali Weak acid.

Question No. 2 - How lime and sand are used to make glass?

Answer No. 2 - Water glass or soluble glass Sodium Silicate is prepared by fusing sodium carbonate Lime with pure sand silica. This process is carried out in a furnace called reverberate furnace.
Na2CO3+ SiO2------>Na2SiO3+ CO2

Question No. 3 - Discuss chemistry of borax bead test?

Answer No. 3 - Borax when fused is decomposed into sodium metaborate and boric anhydride.
Na2B4O7----->2NaBO2+B2O3

Question No. 4 - CO2 is a gas while SiO2 is solid at room temperature. Justify?

Answer No. 4 - Silicon atoms are much larger than carbon atoms and thus tend to surround themselves with more oxygen neighbours. Silicon forms only single bonds to oxygen atoms whereas carbon may form double bonds. Carbon in fact forms double bond to each of the two oxygen atoms to produce a small, symmetrical, linear molecules CO2, which is volatile and reasonably reactive.

Question No. 5 - Write any two properties of boron which show peculiar behavior?

Answer No. 5 - 1. Boron is only element in Group IIIA which is non
metallic in behaviour.
2. It is the only element with less that four electrons in
the outermost shell which is not a metal.

Question No. 6 - What are silicates? Give example.

Answer No. 6 - Compounds derived from silicic acid H2SiO3 are calledilicates. For sodium silicate Na2SiO3, it is a sodium salt of metasilicic acid.
Na2CO3+ SiO2-------> Na2SiO3+ CO2

Question No. 7 - How borax is commercially prepared?Give two methods of preparation.

Answer No. 7 - i Borax is prepared by treating a hot solution of boric acid with proper amount of soda ash:
4H3BO3+ Na2CO3--------> Na2B4O7+ 6H2O + CO2

Question No. 8 - Aluminium sheets are said to be corrosion-free. Comment.

Answer No. 8 - When a sheet of aluminium is exposed to moist air it acquires a thin, continuous coating of aluminium oxide, which prevents further attack on the metal by atmospheric oxygen and water under normal conditions. Because of this aluminium sheets are said to be corrosion-free.

Question No. 9 - Boron differs from its family members, Discuss?

Answer No. 9 - 1. Boron is only element in group IIIA which is non
metallic in behaviour.
2. Its is the only element with less than four electron in
the outermost shell which is not a metal.
3. One of the outstanding feature of the chemistry of boron
is its ability to form molecular addition compounds.

Question No. 10 - What is asbestos? Give its two uses.

Answer No. 10 - Asbestos is hydrated calcium magnesium silicate CaMg3SiO34. It commonly used in making incombustible fabrics and hardboards, etc.

Question No. 11 - Give common property of group IVA elements of periodic table.

Answer No. 11 - All the elements of this group show a valency of four.

Question No. 12 - Write any use of borax.

Answer No. 12 - It is used to prepare borate glass, which is heat resistant.

Question No. 13 - Give the formula and use of Talc soap stone?

Answer No. 13 - Formula of soap stone: Mg3H2SiO34

Question No. 14 - What is effect of temperature on semiconductor?

Answer No. 14 - The electrical conductivity of semiconductor depends upon their temperature. When a metal is heated, its resistance increases, when a semiconductor is heated its resistance decreases and vise versa.

Question No. 15 - How Clay Articles are glazed?

Answer No. 15 - Clay articles are glazed by boric acid because borate glazes possesses a higher coefficient of expansion.

Question No. 16 - How weathering of potassium feldspar takes place? Give chemical equation also.

Answer No. 16 - Many important silicate rocks contain aluminium.The weathering of these rocks results in the disintegration of the complex silicates which they contain. The boiling and freezing of water in the rocks and the chemical action of water and carbon dioxide convert these compounds into potassium carbonate, sand and clay. The following reaction explain the weathering of potassium feldspar:
K2O.Al2O3.6SiO2+ H2CO3+H2O------>K2CO3+ 4SiO2+Al2O3.SiO22.2H2O

Question No. 17 - Write the behavior of Al with conc. HNO3?

Answer No. 17 - Aluminium does not react with nitric acid at any concentration, probably because of the formation of protective layer of aluminium oxide.

Question No. 18 - Outline any four uses of aluminium?

Answer No. 18 - i It is non-magnetic and is thus used in navigational equipment.
ii It is non toxic and can be used for making food and brewing equipment and is packaging.
iii Aluminium readily forms alloys with other metals like copper, magnesium, nickel and zinc.
At home, aluminium is found in the form of cooking utensils, window frames and kitchen foil.

Question No. 19 - White lead is not a good pigment. Give reason?

Answer No. 19 - Basic lead carbonate 2PbCO3.PbOH2 is an amorphous white pigment. White lead is not suitable for use as good pigment since it is darkened by the hydrogen sulphide which is frequently present in the atmosphere.

Question No. 20 - Under what conditions aluminium corrodes?

Answer No. 20 - When aluminium sheet is exposed to moist air it acquires a thin, continuous coating of aluminium oxide, which is product of aluminium corrosion.

Question No. 21 - Which elements and compounds can act as semiconductors?

Answer No. 21 - Elements: Semiconductor include the elements germanium, selenium and silicons.

Question No. 22 - State procedure by which surface of stoneware is made less porous?

Answer No. 22 - Stoneware are 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 aluminium silicate, which melt readily and cover the entire surface. When the article cools, the covering solidifies, producing a compact, smooth and waterproof surface.

Question No. 23 - How does Aluminium react with a NaOH b H2SO4.

Answer No. 23 - Alluminiumis dissolved in sodium hydroxide to give soluble aluminate, with the evolution of hydrogen.
Al + 2NaOH-----> + 6H2O----->NaAlOH4+ 3H2

Question No. 24 - Why liquid silicones are preferred over organic lubricant?

Answer No. 24 - The outstanding physical attribute of silicone oil is its very small change in viscosity with changing temperature, compared with the behavior of other oils of similar viscosity. If the temperature is ped from 100°C to 0°C the viscosity of petroleum oil may increase about one hundred folds, whereas, that of silicons oils will increase less than four folds in the presence of air or oxygen at temperature as high as 300°C silicon oils remain free from acid formation,oxidation and similar phenomenon, which frequently limit the usefulness of petroleum products and other synthetic organic liquids.

Question No. 25 - What happens when borax is treated with HCl and H2SO4 separately?

Answer No. 25 - Aqueous solution of borax reacts with HCl or H2SO4 to form boric acid.
Na2B4O7+ 2HCI + 5H2O------->4H3BO3+ 2NaCI
Na2B4O7 + H2SO4+ 5H2O------>4H3BO3+ Na2SO4

Question No. 26 - Write one point to show peculiar behavior of carbon.

Answer No. 26 - Carbon differs from remaining members of group IV-A the following respects.

Question No. 27 - In what respects, carbon behaves differently from other members of group IV-A?

Answer No. 27 - Carbon differs from the remaining members of Group IVA in following respects. Carbon and silicon are non-metals while the other members of the family are metalloids or metals.

Question No. 28 - Borate glazes are better than silicate glazes. Explain?

Answer No. 28 - Boric acid is used in pottery as a glaze because glazes are more fusible than silicate glazes and possess a higher coefficient of expansion.

Question No. 29 - Describe composition and used of chemical garden?

Answer No. 29 - When crystals of soluble coloured salts like nickle chloride, ferrous sulphate, cooper sulphate or cobalt nitrate, etc. The placed in a solution of sodium silicate, they produced a very beautiful growth, like plant, which is called chemical garden.

Question No. 30 - How does H3BO3 act as an acid?

Answer No. 30 - i Boric acid turns blue litmus red.
ii Boric acid partially neutralized by caustic soda to give borax.
4H3BO3+ 2NaOH------>Na2B4O7+ 7H2O

Question No. 31 - Write the names and chemical formulas of four boric acids?

Answer No. 31 - Name Formulae
i Orthoboric acid H3BO3
ii Metaboric acid HBO2
iii Tetraboric acid H2B4O7
iv Pyroboric acid H6B4O9

Question No. 32 - Show that H3BO3 is mono basic acid?

Answer No. 32 - H3BO3 is a very weak acid and ionizes to a very limited extent mainly as a mono basic acid.
H3BO3 + H2O ----->{BOH4} + H+

Question No. 33 - Under what conditions aluminium corrode.

Answer No. 33 - When aluminium sheet is exposed to moist air it acquires a thin, continuous coating of aluminium oxide, which is product of aluminium corrosion.

Question No. 34 - Write use of Sodium Silicate?

Answer No. 34 - It is used as filler for soap in soap industry.

Question No. 35 - Write the formula of Borax and Chile Saltpeter.

Answer No. 35 - Borax: Na2B4. 10H2O
Chile Saltpeter : NanO3

Question No. 36 - What is the action of an aqueous solution of Borax on litmus.

Answer No. 36 - Aqueous solution of borax is alkaline in nature due to hydrolysis. It will turn red litmus to blue.
Na2B4O7 + 7H2O------>2NaOH + 4H3BO3
Borax Strong alkali Weak acid

Question No. 37 - Aluminium is not found free in nature. Comment the statement?

Answer No. 37 - It occurs primarily as alumino-silicate minerals found in the rocks of the outer portion of the earth. So, Aluminium is not found free in nature.

Question No. 38 - What is meant by chemical garden?

Answer No. 38 - When crystals of soluble coloured salts like nickle chloride ferrous sulphate, copper sulphate or cobalt nitrate, etc. Are placed in a solution of sodium silicate, they produced a very beautiful growth, like plant, which called chemical garden.

Question No. 39 - Boric acid can be converted to borax and vice versa. Give reaction?

Answer No. 39 - Conversion of boric acid into borax: Borax is prepared by treating a hot solution of boric acid with proper amount of soda ash:
4H3BO3+ Na2CO3-------> Na2B4O7+ 6H2O +CO2

Question No. 40 - Write use of silicons.

Answer No. 40 - They are used in hydraulic brakes and other hydraulic system.

Question No. 41 - Give reaction of Aluminium with dilute and concentrated H2SO4?

Answer No. 41 - Reaction with dilute H2SO4: Aluminium does not react with dilute sulphuric acid.

Question No. 42 - Why Boric acid cannot be titrated by NaOH?

Answer No. 42 - Boric acid is partially neutralized by caustic soda to give borax so, boric acid cannot be titrated by NaOH.
4H3BO3+ 2HaOH------->Na2B4O7+ 7H2O

Question No. 43 - What is vitreous silica? Give its two uses?

Answer No. 43 - When crystalline silica is heated sufficiently it melts to give a viscous liquid having a random structure, presumably with the silicon atoms still on the average closed to four oxygen atoms and the oxygen atoms close to two usually it under cools tremendously and eventually becomes rigid without having undergone orientation into a regular crystal pattern.

Question No. 44 - How semiconductors are used in transistors?

Answer No. 44 - Semiconductors may joined to other material, which may be a metal or a different semiconductor. The junction between the different materials form a boundary. It allows electricity to pass more properly and is used in transistors.

Question No. 45 - Give uses of Lead Suboxide?

Answer No. 45 - It is back powder obtained on heating plumbous oxalate in the absence of air. Other than pigments, it is used in the manufacture of lead storage batteries.

Question No. 46 - How Aluminium reacts with aqueous sodium hydroxide?

Answer No. 46 - Aluminium dissolves in sodium hydroxide to form a soluble aluminate with the evolution of hydrogen.
2AIs+ 2NaOHaq+ 6H2OI------->2NaAIOH4aq+3H2g

Question No. 47 - Justify that solubility of borax changes with change in temperature.

Answer No. 47 - It is sparingly soluble in cold water but is more soluble in hot water: 100 grams of water dissolve 3 gram of decahydrate at 10°C and 99.3 grams at 100°C.

Question No. 48 - Give two similarities between carbon and silicon.

Answer No. 48 - Carbon and silicon both form acidic oxides where as other oxides areamphoteric in nature.

Question No. 49 - What happens when borax is heated with NH4CI?

Answer No. 49 - When borax is heated when ammonium chloride boron nitridride is produced.

Question No. 50 - Discuss use of PbCrO4 in paints?

Answer No. 50 - It is used as a pigment under the name of chrome yellow. Orange or red basic lead chromates are formed when lead chromate is boiled with dilute alkali and are used as pigments. The stable yellow modification of lead chromate is monoclinic Mixture of lead chromate with lead sulphate or barium sulphate are also used as yellow pigments.

Question No. 51 - Discuss that CO2 is acidic in character.

Answer No. 51 - CO2 gas when dissolved in water gives H2CO3 an acid. The reaction is given below as:
CO2+ H2O------->H2CO3

Question No. 52 - In which way Al becomes water soluble by using NaOH?

Answer No. 52 - Aluminium dissolves in sodium hydroxide to form a soluble aluminate, with the evolution of hydrogen.
2Als+ 2NaOHaq+ 6H2OI---->2NaAIOH4aq+ 3H2g

Question No. 53 - Write down the use of boric acid.

Answer No. 53 - Boric acid are used in medicines as an antiseptic, e.g dusting powder, boric ointment and boric solution is used as an eye wash.

Question No. 54 - What is reaction of heat on orthoboric acid, H3BO3?

Answer No. 54 - When orthoboric acid is heated strongly, it swells to frothy mass losing water molecules. It is first converted into metaboric acid then to tetra boric acid and finally to boric anhydride.

Question No. 55 - How is borax converted into boric acid vice versa?

Answer No. 55 - A hot concentrated solution of borax is treated with a calculated quantity of concentrated H2SO4. On cooling, crystals of boric acid formed separated out.
Na2B4O7 + H2SO4 + 5H2O------>Na2SO4 + 4H3BO3
Borax Boric acid

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