Ques 1: a) Due to which property of metals are metallic foils prepared?
b) Write uses of aluminium foils
Ans: a) Metallic foils are prepared, making use of the malleable property of metals.
b) Aluminium foils are used for
(i) wrapping chocolates and food stuff
(ii) to prepare hydrogen.
Ques 2: Name one non-metal and one metal, which are in liquid state at room temperature.
Ans: Bromine is the non–metal and mercury is the metal which are in liquid state at room temperature.
Ques 3: Give reasons for the following
i) Zinc oxide is considered an amphoteric oxide.
ii) Non-metals in general do not displace hydrogen from dilute acids.
iii) Metals conduct electricity.
Ans: i) Zinc oxide is considered an amphoteric oxide because it shows both acidic and basic behaviour.
ii) Non-metals do not react with dilute acids hence do not displace hydrogen from dilute acids.
iii) thatMetals conduct electricity because they contain free electrons which can move easily through the metal and conduct electric current.
Ques 4: Identify the following oxides with neutral, acidic, basic and amphoteric oxides.
Ans: Neutral oxides: CO; N2O
Acidic oxides: SO2; CO2; SO3
Basic oxides: MgO; Na2O; CaO
Amphoteric oxides: Al2O3 ; ZnO
Ques 5: By what processes do you concentrate the following ores:
iii) Al2O3.2H2O (bauxite).
Ans: i) PbS (galena) is concentrated by froth floatation method.
ii) Fe2O3 (haematite) is concentrated by magnetic separation.
iii) Al2O3.2H2O (bauxite) is concentrated by leaching process (chemical method).
Ques 6: Why is that iron does not occur as a metal in the crust of the earth? What are the common compound forms in which iron occurs? Which of these is more often used for extracting iron? Why are carbon and limestone mixed with iron ore before feeding it into the blast furnace? Write the chemical equations for the reduction step and the slag formation step.
Ans: Iron is quite reactive and so it does not occur as a metal in the crust of the earth. The common compounds formed are its oxide, a carbonate and a sulphide. The oxide ore of iron called haematite is more often used for extracting iron. The carbon and limestone which is mixed with iron ore is called the charge. This charge is responsible for the formation of iron metal. Coke acts the reducing agent and addition of limestone helps to remove the earthy impurities like sand from the blast furnace by forming fusible slag.
Reduction of Iron(III)oxide or haematite to Iron: carbon monoxide reduces iron(III)oxide to iron metal
Reduction of Iron (III) oxide or haematite to Iron: carbon monoxide reduces iron (III) oxide to iron metal
Fe2O3(s) + 3CO(g) → 2Fe + 3Co2(g)
(i) In the blast furnace limestone decomposes to form calcium oxide and carbon dioxide.
CaCO3 (s) → CaO(s) + CO2(g)
(ii) This clacium oxide reacts with sand for form molten calcium silicate called slag.
CaO(s) + SiO2 → CaSiO3(I) (slag.)
Ques 7: By what chemical processes do you obtain the following metals?
i) Mercury from HgO
ii) Iron from Fe2O3
iii) Manganese from MnO2
iv) Sodium form NaCl
v) Aluminium from Al2O3.
Ans: (i) Mercury from mercuric oxide can be obtained by simple heating.
2HgO → 2Hg +O2
(ii) Iron from iron oxide (Fe2O3) can be obtained by carbon reduction method i.e heating with coke.
2C +O2 → 2CO
Fe2O3 +3CO → 2Fe + 3CO2
(iii) Manganese from manganese dioxide is obtained by alumino thermite process, i.e. heating with aluminium.
3MnO2 + 4AI → 2AI2O3 + 3Mn
(iv) Sodium from sodium chloride is obtained by electrolytic reduction (electrolysis) of fused NaCl.
NaCl ⇌ Na+ + Cl-
At anode 2Cl- → Cl2 + 2e-
At cathode 2[Na= + e- → Na]
(v) Al2O3 ⇌2Al3+ + 3(O)2-
At cathode 4[2Al3+ + 6e → 2AI]
At anode 6O2- → 3O2 + 12e-
Ques 8: i) What is the composition of molten slag, formed in the extraction of iron in the blast furnace?
ii) What is the use of slag?
Ans: i) Molten slag in the extraction of iron is calcium silicate(CaSiO3).
ii) Slag is used for constructions of roads.
Ques 9: Write the name of the compound, when iron is corroded?
Ans: When iron is corroded rust is formed which is hydrated iron (III) oxide (Fe2O3.x.H2O)
Ques 10: Give reasons for the following
i. Na, K and Ca metals form hydrides by combination with hydrogen gas, but most other metals do not.
ii. Aluminium easily combines with oxygen but still it can be used for making kitchen utensils.
Ans: i. Metals like Na, K and Ca can force the hydrogen atoms to accept electrons given by them and form hydrides.
ii. Aluminium forms a protective oxide layer when it combines with oxygen and hence it is used for making kitchen utensils.
Ques 11: i) Among iron and aluminium which rusts easily?
ii) What are the conditions, necessary for rusting of iron?
Ans: i) Among iron and aluminium, iron rusts easily. It forms Al2O3. That is why iron pipes are wrapped with aluminium metal to prevent rusting of iron.
ii) 1) Air or oxygen 2) Water, containing dissolved air.
These are necessary conditions for rusting of iron.
Ques 12: Name an ore of zinc other than zinc oxide. By what process can this ore be converted to zinc oxide.
Ans: Zinc blende (ZnS) is an ore of zinc other than zinc oxide. Roasting is the process by which ZnS can be converted into zinc oxide.
Ques 13: What property of hydrogen is observed in the following experiments?
i) Balloon, filled with hydrogen, floats.
ii) Pop sound is heard when a burning splint is introduced at the mouth of hydrogen filled jar.
iii) When black cupric oxide is heated in a stream of hydrogen, reddish colour is obtained.
Ans: i) Hydrogen is light. So hydrogen filled balloons float.
ii) Pop sound is due to the combustible property of hydrogen. Hydrogen burns with oxygen at the mouth of the hydrogen filled jar.
iii) Hydrogen has reducing property. Hence it reduces black cupric oxide to red copper metal.
Ques 14: Select the non-metals amongst the following
Ans: Hydrogen and Sulphur are the non-metals.
Ques 15: How do you test ammonia gas?
Ans: Ammonia gas is tested, by showing a drop of conc. HCl by means of a glass rod to it, when dense white fumes of ammonium chloride are formed.
Ammonium chloride (dense white fumes).
Ques 16: Write chemical equations for reactions taking place when
i) Cinnabar is heated in air.
ii) Concentrated sulphuric acid and sulphur are heated together. Calcium metal reacts with water.
Ans: (i) Cinnabar is heated in air
2HgS + 3O2 (g) → 2HgO (s) +2SO2
(ii) Calcium metal reacts with water.
Ca(s) + 2H2O(I) → Ca(OH)2(aq) + H2(g).
Ques 17: What are the uses of ammonia?
Ans: i) Ammonia is used in the manufacture of fertilizers like ammonium sulphate and ammonium nitrate.
ii) To manufacture nitric acid by Ostwald’s process.
iii) To prepare dyes, explosives, cellulose acetate etc.
Ques 18: Why do some metals like, Na, K, Ca, Mg not occur in nature as free elements?
Ans: Metals like Na, K, etc (alkali metals) and Ca, Mg etc (alkaline earth metals) are very reactive and hence they react with atmospheric oxygen and carbon dioxide and also with other non-metals like sulphur present in the earth’s crust to form compounds like oxides, carbonates, sulphides, sulphates and chlorides. So they do not occur in free state, but are found in the form of the above compounds.
Ques 19: Write chemical equations for reactions taking place when:
i) Manganese dioxide is heated with aluminium powder.
ii) Steam is passed over hot iron.
iii) A mixture of ammonia and oxygen is passed over platinum heated to 1073 K.
(i) Manganese dioxide is heated with aluminium powder.
(s) + 4AI(s) → 3Mn(I) + 2Al2
(ii) Steam is passed over hot iron.
3Fe(s) + 4H2
O → Fe3
(s) + 4H2
(iii) A mixture of ammonia and oxygen is passed over platinum heated to 1073K
(g) + 5O2
(g) → 4NO(g) + 6H2
O.Ques 20: Why are metals like sodium, calcium, magnesium, aluminium etc. obtained by electrolytic reduction?
Metals like Na, Ca, Mg, Al etc, which are high up in the activity series are electropositive elements and possess a high affinity for oxygen. So their oxides are very much stable and cannot be reduced with common reducing agents like carbon. So carbon reduction process cannot be applied to prepare these metals. They can only be prepared by electrolytic reduction of their fused chlorides or oxides.Ques 21: State briefly how you will extract iron from its ore. Draw a neat and labelled diagram. Write all the chemical reactions involved in it.
Iron is usually extracted from its chief ore, Haemitite.
The various steps involved in the production of iron metal from haematite are as follows:
1. Concentration of ore
The concentration of haematite or is done by the method of hydraulic washing. The ore is spilt into small pieces and then washed in a stream of water to remove sand, clay. In this way ,a fairly concentrated ore is obtained and usually there is no need of any further concentration.
The washed iron ore is then strongly heated in the absence of air to expel water sticking to it.
The washed and dried ore is mixed with weighed quantities of coke and limestone and put into a blast furnace from the top. A blast of hot air is blown into the furnace from near its bottom. This air is to supply for the burning of coke.
The two reactions which take place in the blast furnace leading to the formation of iron metal are: formation of carbon monoxide and reduction of haematite.
1) Formation of carbon monoxide
Carbon monoxide is the main reducing agent in the extraction of iron by blast furnace. Carbon monoxide is formed from coke in two steps:
Near the bottom of the furnace coke burns in air to form carbon dioxide and a lot of heat is produced
C(s) + O2
In the center of the furnace, carbon dioxide reacts with white hot cake to form carbon monoxide.
+ C(s) → 2CO
2) Reduction of Iron (III) oxide to Iron
In the upper part of the furnace, carbon monoxide reduces iron (III) oxide to iron metal
+ 3CO → 2Fe(I) + 3CO2
Iron metal is produced as a grey solid which melts as it comes down in the furnace where the temperature is very high. Molten iron collects at the bottom of the furnace.
Ques 22: Write the chemical formula for the following.
f) Sodium amalgam
|a) Alumina||– Al2O3|
|b) Silica||– SiO2|
|c) Rust||– Fe2O3. xH2O|
|d) Oleum||– H2S2O7 (SO3, dissolved in H2SO4)|
|e) Slag||– CaSiO3|
|f) Sodium amalgam||– Na – Hg (an alloy of sodium with mercury)|
|g) Bauxite||– Al2O3.2H2O|
|h) Haematite||– Fe2O3|Ques 23: In Frasch process of digging out sulphur from a deep underground, how has it made possible to life sulphur from the bed to surface of each? What is the basic principle on which extraction of sulphur is based? Draw a neat and labelled diagram. Besides elemental form, in what compound forms is sulphur found. Give two physical properties of sulphur.
In the Frasch process in order to bring out sulphur from the underground deposits, a hole of about 30 cm diameter is bored up to the sulphur bed. It is based on the principle that sulphur has a comparatively low melting point of 1150
due to which it can be melted by introducing super-heated water in the underground sulphur deposits. This mixture of molten sulphur and water is then brought out by the force of hot, compressed air.
Three concentric pipes A, B, C of different diameters are put down in the boring.
The three pipes are arranged one inside the other as shown in the above figure. Super-heated water under pressure is forced down through the outermost pipe A. The heat given out by hot water melts the underground sulphur. A jet of hot, compressed air is then sent down through the innermost pipe C. The force of compressed air brings the mixture of molten sulphur and water through the central pipe B. The sulphur water emulsion is kept in settling tanks when sulphur gets cooled and separates from water in the form of a yellow solid. The sulphur obtained by this method is 99.5% pure.Ques 24: The copper vessels used in homes are found to be coated with green colour. Answer the following.
a) What is the chemical composition of the green coating?
b) Why do copper vessels form such a green coating?
c) What is the name of the phenomenon, responsible for the green coating?
d) Copper vessels are best cleaned with tamarind or lemon juice, but not with soap. Why?
a) Green coloured coating on copper is due to the formation of basic copper carbonate, CuCO3
b) Copper forms green coating of basic copper carbonate as it reacts with water, atmospheric oxygen and carbon dioxide.
c) Corrosion phenomenon is responsible for the formation of basic copper carbonate (green).
d) Since basic copper carbonate is basic in nature, it can be removed by tartaric acid present in tamarind or citric acid, present in lemon. Soap is basic in nature. So copper vessels are best cleaned with tamarind or lemon.Ques 25: Give reasons for the following
(i) Silicon counts among metalloids
(ii) Carbon is not used for making aluminium from aluminium oxide.
(iii) For making hydrogen by reaction with hydrochloric acid, granulated zinc is preferred to a block of zinc.
(i) Silicon shows properties of both metals and non-metals and hence silicon counts among metalloids.
(ii) Carbon has less affinity for oxygen than Aluminium and hence it cannot eliminate oxygen from Aluminium oxide.
(iii) Zinc granules are preferred to a block of zinc because it offers a large surface area for the reaction with the acid.Ques 26: Explain
(i) Why sugar chars (turns black) when conc. H2SO4 is added to it?
(ii) What is the blue colour of crystalline copper sulphate due to?Ans:
ii) Blue colour of crystalline copper sulphate is due to five water molecules of hydration in CuSO4
O.Ques 27: Write chemical equations for reactions taking place when
(i) Zinc carbonate is calcined.
(ii) Ammonia gas is passed over heated copper (II) oxide.
Ques 28: (i) What is the colour of potassium dichromate solution?
(ii) What is the colour of Cr3+ ion?
(iii) What property of SO2 is responsible for bringing change of colour of potassium dichromate?
(i) Potassium dichromate solution is orange yellow colour.
(ii) The colour of Cr3+
ion is green.
(iii) Reducing property of sulphur dioxide is responsible to change the orange yellow colour of K2
to green colour.Ques 29: How is chloride of lime chemically different from calcium chloride? Why does chloride of lime gradually lose its chlorine when kept exposed to air?
Chemically, chloride of lime is calcium oxy chloride, CaOCl2,
also called bleaching powder. When exposed to air it gradually lose its chlorine because it reacts with carbon dioxide present in air to produce calcium carbonate and chlorine gas.Ques 30: Write short notes on the bleaching action of sulphur dioxide.
a) Sulphur dioxide bleaches the vegetable colours in the presence of moisture.
b) It bleaches the vegetable colours by reduction. It removes oxygen from coloured material.
c) Its bleaching action is temporary, because atmospheric oxygen again oxidises the bleached article back to its original colour.
is used to bleach delicate fabrics like wool, silk etc.Ques 31: (a) What is the atomicity of sulphur?
(b) How do you bring the change of rhombic sulphur to monoclinic sulphur and vice versa?
(c) What is the action of conc. HNO3 on sulphur?
(a) Atomicity of sulphur is 8. Its formula is S8
(b) Rhombic sulphur, when heated to above 369K, reverts back to rhombic sulphur.
(c) Conc. HNO3
oxidises sulphur to sulphuric acid while the former is reduced to NO.
S(s) + 6HNO3
(aq) → H2
(aq) + 6NO2
(g) + 2H2
O(I)Ques 32: Name two metals used in making fuse wires.
Copper and Aluminium are the two metals used in making fuse wires.Ques 33: (i) How can ammonia be converted to NO2 and nitric acid?
(ii) What is liquor ammonia?Ans:
(i) When ammonia is oxidised by heating with oxygen to 1073 K in the presence of platinum gauze, reddish brown vapours of NO2
dissolves in water, nitric acid is formed.
O + O → 2HNO3
is manufactured from ammonia.
(ii) A saturated solution of ammonia is known as liquor ammonia.Ques 34: Complete the following reactionsAns:
COONa + C2
CHO + H2
O.Ques 35: Define the following terms
i) The inorganic elements or compounds which occur naturally in the earth’s crust are known as minerals.
ii) The minerals from which a metal can be profitably extracted are called ores.
iii) The impurity of sand and rocky materials present in the ore is known as gangue.Ques 36: a) State why hydrogen is said to be a clean fuel?
b) What property of hydrogen is involved in being a good fuel?
c) What is hydrogenation of oils? Write one application.
a) Hydrogen is a clean fuel because its reaction with oxygen produces only water. It does not form gases like CO2
etc, which pollute air.
b) Hydrogen, on combustion with oxygen, produces water and a lot of heat. This is an exothermic reaction.
c) Oils are unsaturated molecules, containing double bond. So hydrogen atoms are added at the double bonds of the molecules of oil. The reaction of hydrogen with oils is known as hydrogenation.
The hydrogenation reaction takes place at 473 K and in the presence of nickel catalyst.
Vanaspati or dalda ghee is prepared by hydrogenation of vegetable oils.Ques 37: What is the formula of Ammonia? Write the flow diagram for the manufacture of ammonia by Haber’s process. State any two of its physical properties. Write the equation for its reaction with HCl.
The formula of Ammonia is NH3
The flow diagram of the manufacture of ammonia by Haber’s process is given below:
1. Ammonia is a colourless gas having a characteristic pungent smell.
2. Ammonia is highly soluble in water.Ques 38: How do metals react with hydrogen? Explain with an example.Ans:
Only very few reactive metals like sodium, potassium, calcium and magnesium react with hydrogen to form metal hydrides. Example when hydrogen gas is passed overheated sodium, sodium hydride is formed.Ques 39: Name a metal which is stored in kerosene oil.Ans:
Sodium is a metal which is stored in kerosene oil.Ques 40: Metals are electropositive in nature. Explain.
Metals are electropositive in nature because they can form positive ions by the loss of electrons.Ques 41: Explain the displacement of hydrogen by a metal from an acid with an example. Give the equation to support the same.
Ans:Ques 42: Why is sodium kept in kerosene?Ans:
Sodium reacts so vigorously that they catch fir if it is kept in the open air and hence sodium is kept in kerosene.Ques 43: Name the element or compound which is associated with Hall’s process.Ans:
Aluminium is associated with Hall’s process.Ques 44: Which metal is used in nuclear reactors and aerospace projects?Ans:
Aluminium is used in nuclear reactors and aerospace projects.