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12th Class Chapter 2 Chemistry Short Questions

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Question: 1
Why lime is added to acidic soil?
Answer: 1
1-41
Addition of lime to acidic soil:Large quantities of calcium oxide are used in agriculture for neutralizing acidic soils.It has been found that application of lime to acidic soils increases the amount of readily soluble phosphorus.
Calcium oxide is also used in large amounts for making lime-sulphur sprays which have as strong fungicidal action.The hydroxide of calcium is obtained when the oxide of the calcium is allowed to react with water.The process is called slaking of lime and it is an exothermic reaction.
CaO+H2O------->Ca(OH)2
Question: 2
Why S-block elements are called as alkali metals and alkaline earth metals?
Answer: 2
2-41
The name alkali came from Arabic,which mean The Ashes.The arab used this term for these metals because they found that the ashes of plants were composed chiefly of sodium and potassium,.Elements of group IA are called alkali metals,because they produce alkaline solutions with water.
Question: 3
Give two uses of Lime in industry.
Answer: 3
3-41
i) Large quantities of lime are used in the extraction and refining of metals.
ii) Lime is used in paper,cement and leather industries.
Question: 4
Why lime water turns milky CO2but becomes clear with excess CO2?
Answer: 4
4-41
A saturated solution of Ca(OH)2is called lime water and is used as a test for CO2.When lime water reacts with CO2it turns to CaCO3(lime stone) which is a solid product.Thus lime water turns milky due to the presence insoluble suspension of calcium carbonate,as shown by following reaction.
Ca(OH)2aq+ CO2g------------->CaCO3s+ H2O
Question: 5
Write the formulas of:a) Beryl b) Sylvite.
Answer: 5
5-41
a) Beryl b)Be3Al2(SiO3)2 c) Sylvite d) KCl
Question: 6
Which Elements are called as alkaline earth metals?Why this name is used for these elements?
Answer: 6
6-41
Elements of group IIAare called alkaline earth metals.The alkaline earth metals are beryllium,magnesium,calcium,strontium,barium and radium.They are called alkaline earth metals because they produce alkalies in water and are widely distributed in earth crusts.
Question: 7
Why Calcium is essential for the normal growth of plants?
Answer: 7
7-41
Use of Calcium in normal growth of Plants:The presence of calcium is essential for the normal development of plants.The quantity of calcium required by different plants varies considerably.An adequate supply of calcium appears to stimulate the development of roots hairs and,infect,the entire root system.
Calcium is also necessary for the normal leave development and tends to accumulate in leaves as well as in bark,an adequate supply of calcium is also essential for the optimum activity of microorganisms that produce nitrates.
Question: 8
How Plaster of Paris is formed.Give its two uses?
Answer: 8
8-41
Formation of Plaster of Paris:When gypsum is heated under carefully controlled conditions.it loses three quarters of its water of crystallization,the resulting product is called Plaster of Paris.Calcium sulphate occurs in nature as gypsum CaSO4.2H2O.When it is heated above 100oC,it loses three quarters of its water of crystallization,giving a white powder which is known as Plaster of Paris.
2CaSO4.2H2O------------->(CaSO4)2.H2O+3H2O
Gypsum Plaster of Paris
Question: 9
Why lithium carbonate decomposes on heating while other alkali metal carbonates remain unaffected?
Answer: 9
9-41
Lithium has low electropositive character,thus its carbonate and nitrate are not so stable and therefore decompose giving lithium oxide.Carbonates of other alkali metals do not decompose.
Question: 10
How Gypsum is converted into Plaster of Paris?
Answer: 10
10-41
When gypsum is heated under carefully controlled conditions,It loses three quarters of its water of crystallization,the resulting product is called Plaster of Paris.Calcium sulphate occurs in nature as gypsum CaSO4.2H2O.When it is heated above 100oC,it loses three quarters of its water of crystallization,giving a white powder which is known as Plaster of Paris.
2CaSO4.2H2O--------->(CaSO4)2.H2O+3H2O
Gypsum Plaster of Paris
Question: 11
Write Chemical Formulae of (a) Carnallite (b) Borax.
Answer: 11
11-41
a) Chemical Formula of Carnallite KCI.MgCl2.6H2O
b) Chemical Formula of Borax Na2B4O7.10H2O
Question: 12
Give the name and formula for common minerals of Be.
Answer: 12
12-41
Name Formula
Beryl Be3Al2(SiO3)2
Chrysoberyl Al2BeO4
Question: 13
What is the function of calcium in plant growth.
Answer: 13
13-41
Function of calcium in plant growth:The presence of calcium is essential for the normal development of plants.The quantity of calcium required by different plants varies considerably.An adequate supply of calcium appears to stimulate the development of roots hairs and,infect,the entire root system.
Calcium is also necessary for the normal leave development and tends to accumulate in leaves as well as in bark,an adequate supply of calcium is also essential for the optimum activity of microorganisms that produce nitrates.The effect of calcium on the supply of available phosphorus in the soil is of special significance.Soils containing sufficient calcium are slightly alkaline in nature.
Question: 14
How Portland cement is made?Why Gypsum is added in the cements?
Answer: 14
14-41
Portland cement:Portland cement is made by strongly heating a finely powdered mixture of clay and limestone.The final product is known as clinker,is cooled and then ground into a very fine powder.
Question: 15
What happen when beryllium react with sodium hydroxide and lithium hydride reacts with water?
Answer: 15
15-41
Beryllium reacts with alkalies to give hydrogen as:
Be+2NaOH---------------------->Na2BeO2+ H2
Question: 16
Lithium is least reactive element of all alkali metals.
Answer: 16
16-41
Lithium is least reactive element of all alkali metals because of its small radius and high charge density.The nuclear charge of Li+ion is screened only by a shell of two electrons.The so called anomalous properties of lithium are due to the fact that lithium is unexpectedly far less electropositive than other alkali metals.
Question: 17
What is the action of litmus with aqueous solution of Na2CO3?
Answer: 17
17-41
The solution of Na2CO3in water is basic due to hydrolysis of carbonate ion.So,it will turn red litmus to blue.
Na2CO3+2H2O------------>2NaOH + H2CO3
Question: 18
When sodium reacts with water,hydrogen which evolves catches fire,Why?
Answer: 18
18-41
A small piece of sodium floated on water reacts vigorously to liberate hydrogen and produce metal hydroxide.The reaction is highly exothermic.The energy produced by the reaction may even ignite the hydrogen.
2Na + 2H2O----------->2NaOH+H2
Question: 19
Write any two points of difference of Be with its family members.
Answer: 19
19-41
Beryllium is the lightest member of the series,.The main points of difference are:
1) Beryllium metal is almost as hard as iron and hard enough to scratch glass.The other alkaline earth metals are much softer than beryllium but still harder than the alkali metals.
2) The melting and boiling points of beryllium are higher than other alkaline earth metals.
Question: 20
Why aqueous solution of Na2Co3is alkaline in nature?
Answer: 20
20-41
The solution of Na2CO3in water is alkaline due to hydrolysis of carbonate ion.So it will turn red litmus to blue.It produces an acid and base,but the base is stronger than that of acid.So the aqueous solution of Na2CO3is alkaline in nature.
Na2CO3+ 2H2O -----------> 2NaOH + H2CO3
Question: 21
What happens when: 1) Li2CO3 2) Na2CO3is heated.
Answer: 21
21-41
Lithium has low electropositive character,thus its carbonate are not so stable and therefore decomposed giving lithium oxide on heating.
Li2CO3----------------->Li2O + CO2
Question: 22
Give reactions of BeO with a) NaOH b) H2SO4.
Answer: 22
22-41
a) Reactions of BeO with NaOH:BeO + 2NaOH------>Na2BeO2+ H2O
b) Reactions of BeO with H2SO4:BeO + H2SO4--------->BeSO4+ H2O
Question: 23
Why group II-A elements are called Alkaline Earth Metals.
Answer: 23
23-41
Group IIA elements are called alkaline earth metals because they produce alkalies in water and are widely distributed in earth's crusts.
Question: 24
Write a brief note on the occurrence of alkaline earth metals?
Answer: 24
24-41
Occurrence of alkaline earth metals:Being very reactive,alkaline earth metals also do not occur in free state,The compounds of these metals occur widely in nature.Magnesium and calcium are very abundant in earth's crust.The outer portion of the earth was originally in the form of silicates and alumino-silicates of alkaline earth metals.Calcium is an essential constituent of many living organisms.It occur as skeletal material in bones,teeth,sea shells and egg shells.Radium is a rare element.It is of great interest because of its radioactive nature.
Question: 25
Complete the reactions: i)Mg3N2+ H2O---->? ii) KO2+ CO2--->?
Answer: 25
25-41
i) Mg3N2+ 6H2O--->2NH3+ 3Mg(OH)2
ii) 4KO2+ 2CO2---->2kO2+ 2CO2---->2K2CO3+3O2
Question: 26
What happened when (a) Lithium Carbonate is heated (b) Beryllium is treated with sodium Hydroxide.
Answer: 26
26-41
Chemical reactions:
(a)Lithium Carbonate is heated:Lithium has low electropositive character,thus its carbonate are not so stable and therefore decomposed giving lithium oxide on heating.
Li2CO3----------------> Li2O + CO2
Question: 27
Give advantages of Down's cell.
Answer: 27
27-41
i) Metallic fog is not produced.
ii) Liquid sodium can easily be collected at 600oC.
iii) Material of cell is not attacked by the products formed during the electrolysis.
Question: 28
How potassium superoxide KO2has very interesting use in breathing equipment for mountains and space crafts?
Answer: 28
28-41
Potassium superoxide KO2has very interesting use in breathing equipment for mountaineers space crafts because it has ability to absord carbon dioxide while giving out oxygen at the same time as: KO2+ 2CO2---> 2K2CO3+ 3O2
Question: 29
Write the advantages of Nelson's cell.
Answer: 29
29-41
i) By using this method sodium hydroxide is manufactured on large scale.
ii) Sodium hydroxide is product of this process but some by products are also achieved like hydrogen gas and chlorine gas.
iii) It is very cheap process because its raw material is sodium chloride which is not costly.
Question: 30
Write the formulae of 1) Natron 2) Dolomite.
Answer: 30
30-41
Formulae of 1)Natron 2) Dolomite
Formula of Natron: Na2CO3.H2O
Formula of Dolomite: MGCO3.CaCO3
Question: 31
Why is CaCl2added in molten Nacl in Down's cell?
Answer: 31
31-41
CaCl2added in molten NaCl in Down's cell: Sodium chloride is used as raw material in Down's cell.The melting point of sodium chloride is 801oC. Some calcium chloride is added to lower the melting point of sodium chloride.Calcium chloride permits the furnace to operate at about 600oC.
Question: 32
Alkali and alkaline earth metals are reactive elements of periodic table.Justify it.
Answer: 32
32-41
Alkali and alkaline earth metals are reactive elements of periodic table because,these elements are most electropositive elements.Alkali metals have only one electron in their valence shell.Ionization energy values of alkali metals are very low.
Question: 33
Mention two major problems that may arise in Nelson's cell.
Answer: 33
33-41
i) Chlorine produced can react with hydroxide ions in cold giving hypochlorite ions.
ii) Hydroxide ions may be attracted toward anode.where they can be discharged releasing oxygen gas.This oxygen gas may contaminate the chlorine and renders it impure.
Question: 34
What is cement plaster and Hard finish plaster?
Answer: 34
34-41
Cement Plaster:It is Plaster of Pairs to which usually glue or other oils have been added as retarders to prolong the time of setting.
Question: 35
Write points to show peculiar behavior of Berylium.
Answer: 35
35-41
1) Beryllium metal is almost as hard as iron and hard enough to scratch glass.
2) Melting and boiling points of beryllium are higher than other alkaline earth metals.
3) Beryllium is least reactive metal in the group.It is resistant to complete oxidation and stable in air a ordinary temperature but oxidize rapidly at about 800oC.
4) Beryllium is not tarnished by atmospheric attack but the metal soon loses the silvery appearance.
2Be + O2800 2BeO
Question: 36
What is mil;k of Magnesia and for which treatment it used.
Answer: 36
36-41
A suspension of Mg(OH)2in water is called milk of magnesia and it is used for the treatment of acidity in stomach.
Question: 37
Give reason that alkali metals are strong reducing agents?
Answer: 37
37-41
The reducing property of an element depends on the magnitude of its ionization energy.Reducing agent is a substance which can lose electron.Since alkali metals have got low ionization energies,so they are strong reducing agents.They are highly electropositive. They react readily with halogens giving alkali metal halides.
Question: 38
What is the role of Gypsum in Agriculture.
Answer: 38
38-41
Role of Gypsum in Agriculture: Gypsum is applied to the soil as source of calcium and sulphur. The calcium supplied by gypsum in fertilizer is of importance in crop production in area where soils are subject to extensive leaching. Sulphur compounds had been applied to soils because of their observed beneficial effect on plants,sulphur has an influence on chlorophyll development in plant leaves.Although not a constituent o chlorophyII,plants deficient in sulphur exhibits a pale green color.The root system of several plants have been observed to be greatly enlarged by the application of sulphur containing materials such as gypsum.
Question: 39
How chlorine produced in Diaphragm cell,is protected to react with Hydroxide ions?
Answer: 39
39-41
Chlorine produced can react with hydroxide ions.To prevent this problem asbestos diaphragm is used.This keeps the two solutions separate while allowing sodium ions to move towards the cathode.This movement of ions keep the current following through the external current.
Question: 40
2% gypsum is added in the cement.Justify.
Answer: 40
40-41
2% gypsum is added in the cement which prevents the cement from hardening too rapidly.The additions of gypsum increases the setting time of cement.
Question: 41
What are main uses of Plaster of Paris?
Answer: 41
41-41
1) Plaster of Paris is used for making plaster walls,casts of statuary,coins,etc.
2) It is used in surgery,Plaster of Paris bandages are used for holding in Place fractured bones after they have been set.
3) It is also used in cement Plaster in which usually glue or other oils have been added as retarders to prolong the time of setting.

12th Class Chemistry Chapters Short Questions