SOUND

1.            What is the frequency range of audible sound?

                The range of audible frequencies is 20Hz to 20,000Hz.

2.            What are ultrasonic waves?

                Sounds waves of frequencies beyond 20 kHz are called ultrasonic waves.

3.            List any six uses of ultrasonic waves?

·         Study of ultrasonic waves gives information about its physical properties like elasticity, configuration of atoms etc.

·         They are used in the manufacturing of alloys, for mixing of immiscible and to manufacture emulsion for photographic films.

·         They are used in the dry cleaning of clothes to remove dirt.

·         They can be used to detect cracks and flaws in metal molding.

·         They are used for welding, local heating and drilling small holes in hard materials.

·         Ultrasonic waves serve as insect repellants and are used for sterilization purposes.

·         They are used to cure neuralgic and rheumatic pains.

·         Surgical instruments vibrating at ultrasonic frequencies are used in bloodless surgery.

·         They can be used to break gallstones and stones in the kidney

4.            What is SONAR? How does it work?

a)      Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

b)      It can be used to find the distance of an object in water and works as follows.

·         SONAR is installed in a boat or ship. It consists of a transmitter and a receiver

·         The transmitter produces and transmits ultrasonic waves. These waves travel through water until they strike an object, reflect and return to the sonar.

·         The time interval between transmission and reception‘t’ recorded. The detector converts the reflected waves into electrical signals and interprets them.

·         If ‘v’ is the velocity of sound through water, then the distance of the object is given by d = vt/2

5.            Using sonar, ultrasonic waves are emitted at the ocean water surface. The ocean bottom reflects these waves. If                 the time interval between the emission of the waves and the detection of the reflected waves is 3.5 seconds,                 find the depth of the ocean.

                Time ‘t’ between the emission of the waves and detection of reflected waves = 3.5 seconds

                Velocity of sound in water ‘v’ = 1.5km/second

                Distance of the object = vt/2

                = 3.5 x 1.5/2 = 2.625km

6.            What is an ultrasonic scanner?

                Ultrasonic scanners are instruments that use ultrasonic waves for getting image of internal organs of human body.

7.            Write a note on the medical applications of ultrasonic waves

·         They can be directed towards specific area of the body. The waves get reflected and provide information about the change in the density of tissues.

·         They are used in scanning, as they are less harmful than X-rays.

·         They are used to obtain information about the internal organs of a body and more so for fluid filled organs like bladders, kidneys and ovaries.

·         It is used in ECG for diagnosing heart diseases and in foetus examination during pregnancy.

8.            Explain Doppler Effect with a suitable example.

·         Imagine, you are standing in a railway platform and a train is reaching you of moving towards you.

·         The frequency of sound increases as it reaches you.

·         You stand in the same position, and if the train leaves the platform, the frequency of sound again decreases.

·         Similar observations are noticed when you are moving and the source is stationery.

·         This change in the frequency due to the relative motion of the observer and the source.

·         This principle of apparent change in frequency is called Doppler Effect.

9.            Mention three applications of Doppler Effect.

                Doppler Effect of sound can be used to

·         Determine the velocity of submarines

·         Detect velocities of vehicles crossing speed limits

·         Track artificial satellites.

10.          Write a note on application of Doppler Effect in astrophysics?

·         Doppler’s effect is found useful in the study of binary stars, Saturn rings, galaxies etc.

·         It is used to estimate the speed of stars, galaxies and rotation of sun’s disc.

·         The red shift observes in the spectrum of the galaxies helps to determine the velocity of the source.

ADDITIONAL IMPORTANT QUESTIONS

1.            How is sound produced?

                Sound produced by the vibration of a body

2.            How is sound propagated?

                Sound is propagated in the form of a wave

3.            How do we hear sound?

                Sound is produced by the vibrations of a body. When these vibrations are registered in our brain, we hear sound

4.            What is a wave? How is it described?

a)      A wave is a periodic disturbance propagating through a medium, carrying energy.

b)      It is described in terms of its frequency (f), wavelength (l) and velocity (v)

5.            Write the equation for a wave and indicate the notations used.

                The equation for a wave is v = fl, where is the frequency, l is the wavelength and v is the velocity

6.            What is audible range?

                The range of frequencies that can be heard by normal human beings is called audible range.

7.            What is ultrasonic sound? What is their range?

a)      Sounds of frequencies beyond 20 kHz are called ultrasonic sounds.

b)      Their frequency ranges from 20 kHz to 5 x 10⁵ kHz.

8.            How are the speeds of the two related audible range ultrasonic range?

                Both are equal.

9.            What is infrasonics? How does it differ from supersonics?

a)      Infrasonics refers to sounds of frequencies lesser than 20Hz.

b)      Supersonics refers to waves of velocities greater than that of sound.

10.          Why do ultrasonic waves have high energy?

                Ultrasonic waves have energy because of their high frequency.

11.          What is a radar gun?

                Radar gun is a device used to detect the vehicles crossing the speed limit.

12.          What is SONAR? Briefly explain one of its uses with an example.

·         Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

·         It can be used to find the distance of objects under water

·         The ultrasound signal sent by sonar takes 3 seconds to return.

·         The velocity of sound in water is 1.5km/second.

·         The distance traveled by the signal

                = 1.5 x 3 = 4.5km

·         Hence, the distance of the object

                = 4.5/2 = 2.25km

13.          Who invented Sonar? Why?

                Paul Langevin invented sonar. It was result of the inspiration by titanic disaster.

14.          What is echo ranging?

                It is technique of finding the distance of under water objects using sonar.

15.          Why are ultrasonic waves preferred for X-rays? Name the best-known application of ultrasonics in medicine.

a)      Ultrasonic waves are preferred because they are less harmful than X-rays.

b)      Examination of foetus during pregnancy is the best-known application of ultrasonics in medicine.

16.          What is Doppler Effect? What changes are observed in the case of light waves?

a)      Doppler Effect is the apparent change in frequency of wave motion due to the relative motion between the source and the observer.

b)      Doppler Effect in light can be observed only in celestial bodies or atomic sources that are moving with high velocities. In the case of light waves, there is a shift in the wavelength of light emitted by celestial bodies.

17.          What is red shift?

                The shift in the color of the light towards the red end of the spectrum when a source emits light of particular                 wavelength and moves away from us are called the re shift.       

SOLAR ENERGY

1.            What is solar energy?

                The energy received from the sun in the form of heat and light is called solar energy.

2.            Mention the different forms of energy derived from solar energy?

                The different forms of energy are wind energy, water energy, energy in food, energy of fossil fuels etc.

3.            What is the main constituent of the sun? Mention the basis on which this was established?

             a) The main constituent of sun is hydrogen.

            b) This was established based on spectrum analysis

4.            Name the nuclear reaction that satisfactorily explains the source of solar energy?

                Nuclear fusion satisfactorily explains the source of solar energy.

5.            Name the two types of nuclear fusion reactions considered to be the source of solar energy?

                The two types are:P – P chain or proton-proton chain wherein four hydrogen nuclei fuse to form a helium nucleus liberating huge amount of energy.Carbon cycle in which carbon acts as a catalyst to favor nuclear action.               The two together accounts for sun’s energy

6.            Give an account of the arrangements in nature to transform solar energy into other forms useful to us.

·         Solar energy transforms itself into wind energy, ocean energy, fossil fuel energy, ocean energy etc.

·         Wind energy: Solar energy heats the air near the earth’s surface and the hot air becomes lighter, moves up and the cooler flows to the lower region causing wind.

·         Water energy: Solar energy heats up water in the water bodies, the water evaporates and forms clouds and bring rain. The rainwater flowing down has kinetic energy and helps to generate electricity.

7.Explain briefly how wind energy is due to solar energy?

·         The box is kept outside in the sunlight and the reflector is adjusted such that a strong beam of sunlight is reflected on the box cover.

·         The sunrays reflected by the reflector, pass through the cover and get absorbed by the black surface of the box and food material inside the container.

·         As a result, the temperature inside the box increases and the food gets cooked.

16. Write a note on solar cooker?

·         Solar cooker is a device used to cook food by directly harnessing solar energy.

·         It works on the principle of thermal conversion and the property of black body to absorb heat.

·         It is pollution free and preserves the nutrients present in the food.

·         It is made of a wooden or an insulating box painted inside with black and covered with a glass sheet that is transparent to infrared radiations of short wavelength and opaque to infrared radiations of longer wavelengths.

·         It cannot be used effectively during night times and on a cloudy day.

18.          Write a note on solar water heater?

·         Solar water heater, as the name suggests is a device used to heat water by directly harnessing solar energy.

·         The water gets heated in the copper tube painted black from outside.

·         Hot water remains in the upper portion of the tank and cold water from the reservoir replaces the hot water and the hot water gets stored in a small cylindrical tank meant for the purpose.

·         The use of solar water heater is pollution free and hence environment friendly, but cannot be used on a cloudy or rainy day.

19.          Write a note on solar cell?

The device that converts solar energy into electrical energy is called a solar device. It consists of a small piece of light absorbing material like silicon Solar energy falling on the material releases electrons from the silicon atoms and produces electricity. It produces a voltage of 0.5V and a power of 0.7W.

Higher voltage and power can be obtained by connecting a series of cells in series. It is used in radio and TV communication, artificial satellites and research centers in remote areas.

ADDITIONAL IMPORTANT QUESTIONS

1.            Mention any two of the characteristics of solar energy?

                The characteristics of solar energy are:

·         It is an inexhaustible source of energy.

·         It is the ultimate source of almost all forms of energy.

2. Why was radioactive decay as the source of sun’s energy rejected?

Solar energy is very much more than the energy that can be released by radioactive decay and hence the  hypothesis was rejected.

3. Who were the first to identify nuclear reaction as the source of solar energy? What was their observation?

a)      Hans Beethe and Cvan Wiezsacker were the first to identify nuclear reaction as the source of solar energy.

b)      They found that hydrogen nuclei fuse to form helium nuclei liberating huge amount of energy as solar energy.

4.            Sun is the ultimate source of almost all forms of energy. Discuss with two examples?

a)      The radiation from the sun provides us heat and light and thus solar energy is converted into heat energy and light energy.

b)      The fossil fuels are formed when living things die and get embedded in the earth’s crust and undergo chemical change. Life forms are due to solar energy and thus fossil fuels are due to solar energy.

c)       The food that we eat is from the plants. Plants need sunlight to prepare their food. Hence solar energy is required for the growth of plants and for the food we eat. Hence, solar energy is the ultimate source of all forms of energy.

7.            The inner surface of a box type solar cooker is painted black. Why?

a)      Black surfaces absorb about 98% of the heat incident on them, while white surfaces do not.

b)      Accordingly, to maximize absorption of heat and minimize heat losses, the inner surfaces of the solar cooker are painted black.

8.            Why are reflectors used in solar heating devices?

Reflectors are used to   Increase the area over which the solar energy is collected.      Focus the sunrays to the required area.

9.            Explain briefly, how the glass sheet used in the solar cooker helps to cook food and increase its efficiency?

a)      The glass sheet used has the following properties:

·         It allows infrared radiation of shorter wave length at high temperature to pass through it.

·         It prevents infrared radiation of longer wavelength at lower temperature to pass through it.

b)      Thus, infrared radiations of shorter wavelength incident on the glass sheet allow them to pass through. When they enter the cooker they heat the body inside and the temperature is reduced resulting in radiations of longer wavelength which are not allowed to go out.

c)       Thus, there is no loss of heat, but the efficiency is increased.

11.          What is a solar cell? On what principle does it work?

a)      Solar cell is a solar electric device by which solar energy is directly converted electrical energy.

b)      It works on the principle of photovoltaic conversion

12.          How are solar cells made?

a)      Solar cells are made using thin wafers of semiconductor material containing impurities.

b)      They are arranged in such a way that when light falls on them, a potential difference is developed between the two regions, which produces electric current.

13.          Explain how the design of a solar cooker ensures minimum loss of heat from its inside?

a)      The thick glass plate used to cover the box ensures minimum loss of heat from inside.

b)      This glass plate has the following properties.

It allows infrared radiations the short wavelengths into the box containing the food to be cooked.When it enters the box, the heat energy is used up by the food for cooking and hence the temperature around it reduces. This results in infrared radiations of longer wavelength, which are not allowed to pass out through the glass plate.

Hence minimum energy is lost from inside

14.          In a solar water heater, copper pipes are bent as a coil. Why?

                Bending copper pipes helps to increase the area of absorption of solar energy and hence are bent.

15.          How are higher voltage and power obtained from solar cells?

                Higher voltage and power are obtained by connecting a number of solar cells in series

16.          What is a solar panel?

                The arrangement of a number of solar cells connected in series is called a solar panel

17.          Mention any four uses of solar cells?

·         Solar cells are used in:  Artificial satellites   Radio and wireless transmission   TV relay stations    Traffic lights.

·         Solar energy heats the air near the earth’s surface.

·         The air becomes warm and lighter

·         It moves up and the cooler air flows to the lower region

·         This causes wind and results in wind energy.

18..  Name the scientists who explained the nuclear reactions as the source of solar energy?

                Hans Bethe and C. Von Weizsacker in 1939

 19..  Name the two types of fusion reactions considered to be the source of Solar energy?

                 (a) Proton – Proton Chain reaction: In which four hydrogen nuclei fuse to form one helium

      (b)Carbon cycle – Here the carbon atom acts as a nuclear catalyst. 

20.  Explain briefly how Solar energy maintains every form of life on the earth

     Basically Solar energy is converted into chemical energy by the plants during photosynthesis. 

    This chemical energy is used by the plants.  A part of this is also flow from plants to herbivorous animals, Man,

    Carnivorous  animals and microbes directly or indirectly depend on plants and  herbivorous animals for their food. 

   This is  how every form   of life on the earth is maintained by solar energy.

21.  Which form of energy is trapped in the fossil fuels?                               Chemical energy

22.  Fossil fuels are non – renewable sources of energy. why?

                Fossil fuels are non-renewable sources of energy, because once we use them they become exhaustible and not

        replenished by the nature immediately, millions of years are required for the formation of fossil fuels.

23.  Name the fossil fuels?          Coal, Petroleum and Natural Gas.

24.  Name the renewable sources of energy.

                Solar energy, Wind energy, Water energy, Atomic energy etc…

25.  Name the component of Solar radiation that mainly carries heat?   Infrared radiation.

26.  Mention the principle on the basis of which solar devices are classified into 2 types?

                (a) In one type of device the solar energy is collected in the form of heat.

                                Ex: Solar cooker, Solar heater, Solar cars etc….

                (b) In the other type Solar energy is converted into electricity.                   Ex: Solar cells

27.  Name the type of mirror present in solar cookers?                  Plane mirror reflector.

28.  Name the type of mirror present in solar water heaters?     Parabolic mirror reflectors (concave mirrors)

29.  What is the function of copper pipe as a coil, in solar water heaters?

                Copper pipes  helps to increase the area for absorption of Solar energy.

metals

Name any two metals that are available in their free state in nature?

                Gold and silver are available in free state in nature

3.            Identify the group and period of the following metals in the periodic table (a) copper (b) iron

a)      Copper belongs to IB group and 4^th period

b)      Iron belongs to V׀׀׀ group and 4^th period

4.            Write the electronic configuration of a copper atom?

                Its electronic configuration is 1s²2s²2p⁶ 3s²3p⁶3d¹⁰4s₁

5.            Write the electronic configuration of an iron atom?

                Its electronic configuration is 1s²2s²2p⁶3s²3p⁶3d⁶4s²

6.            Name the important ores of copper. Write their molecular formula?

                The important ores of copper are:

·         Copper pyrites (CuFeS²)

·         Copper glance (Cu₂S)

·         Cuprite (Cu₂O)

·         Malachite [CuCO₃ Cu(OH)₂]

·         Azurite [2CuCO₃ Cu(OH)₂]

7.            Name the important ores of iron. Write their molecular formula?

                The important ores of iron are:

·         Haematite (Fe₂O₃)

·         Magnetite (Fe₃O₄)

·         Limonite (Fe₂O₃H₂O)

·         Siderite (FeCCO₃)

ADDITIONAL IMPORTANT QUESTIONS

1.            Name two major sources of metals?

                Earth’s crust and seawater are major source of metals

2.            Write the atomic number and mass number of copper?

                The atomic number of copper is 29 and its mass number is 64.

3.            What is rust? Write its chemical formula?

1.       Rust is hydrated oxide of iron.

2.       Its chemical formula is Fe₂O₃2H₂O

4.            Name a metal that does not react with water under any condition?

                Copper does not react with water under any condition.

5.            Name the largest source of metals?

                The earth’s crust is the largest source of metals.

6.            Name two metals that do not react with air?

                Gold and platinum do not react with air.

7.            Name ant two transition elements?

                Copper and iron are transition elements.

8.            Name any two places in India where copper ores are found?

                Copper ores occur in India in Karnataka, Rajasthan, Sikkim and Bihar.

9.            Name the physical nature and the composition of the compound formed on copper when it is burnt in air?

                The compound is a black layer of cuprous oxide.

10.          How do you prevent of rusting of iron?

                Rusting of iron can be prevented by coating it with a layer of zinc or painting.

11.          What happens when sodium is burnt in excess of oxygen?

                When sodium is burnt in excess of oxygen, sodium peroxide is formed

                2Na+O₂⟶Na₂O₂

12.          How does iron react with dry air and pure water?

                Iron does not react in both cases

13.          What is the general product obtained when metals react with oxygen?

                Metals react with oxygen to produce respective oxides.

14.          How does magnesium react with air?

                Magnesium burns in air forming magnesium oxide. 2MG+O₂⟶2MgO

15.          What is a solid solution? How is it prepared?

1.       A solid solution is a homogenous mixture of a metal with one or more metals and nonmetals.

2.       It is prepared in molten state and solidified.

16.          How is copper oxide formed?

                When a foil of copper is burnt in a flame and allowed to cool, after sometime, a black layer is seen on the copper                 foil. This is copper oxide. 2Cu+O₂⟶2CuO

17.          Name the arrangement used to extract iron. Why is it so called? What do you call the iron extracted in it? In                 what form is it obtained?

1.       Iron is extracted using a blast furnace.

2.       It is called so because a blast of hot air is blown into it.

3.       The iron so extracted is called cast iron or pig iron.

4.       It is in molten form.

18.          Mention any two physical properties of iron?

·         Iron is a grayish white solid metal

·         In its pure form it is soft

·         It has a melting point of 1808K

·         It is a ferromagnetic substance

19.          Mention any four physical properties of copper?

·         It is a rose red heavy metal

·         It is malleable and ductile

·         It has high thermal conductivity

·         It has high melting and boiling point.

20.          Describe briefly the reaction of metals with chlorine?

·         All metals react with chlorine to form their respective chlorides.

·         More reactive metals react at room temperature, whereas less reactive metals react on heating the metal.

                Na+CI₂⟶2NaCI

                2AI+3CI₂⟶2FeCI₃

21.          How do metals react with nitric acid?

·         Metals react with very dilute nitric acid to form respective nitrates liberating hydrogen

                Mg+HNO₃⟶Mg (NO₃)₂+H₂↑

·         Metals react with moderately concentrated nitric acid to form respective nitrates liberating nitric oxide

                3Cu+8HNO₃⟶3Cu (NO₃)₂+2NO+4H₂O

·         Metals react with concentrated nitric acid to form metallic nitrates liberating nitrous oxide

                Cu+4HNO₃⟶Cu (NO₃)₂+2NO₂ ↑+2H₂O

22.          Name any three alloys of iron. Mention any two of their uses?

                The alloys of iron are:

·         Stainless steel used in utensils and surgical instruments.

·         Nickel steel used in utensils and drilling instruments.

·         Steel used pipes, nails, sheets and cutting tools.

23.          Mention any two alloys of copper and their uses?

                The alloys of copper are:

·         Brass used for making utensils, electrical appliances, machinery parts etc.

·         Bronze, used for statues, bells coins and utensils.

·         German silver used for utensils, resistance coils and ornamental wares.

·         Gun metal used for barrels of guns, gears and castings.

24.          How do metals react with water? Give two examples?

·         Metals react with water or steam to form respective oxide or hydroxides and liberating hydrogen.

·         Sodium reacts with cold water to produce sodium hydroxide liberating hydrogen.

                2Na+ H₂O⟶2NaOH+H₂↑

·         When steam is passed over hot iron, zinc or magnesium, forming respective oxide and liberating hydrogen.

                3Na+4 H₂O⟶Fe₃O₄+4H₂↑

25.          Write balanced chemical equations for the following: (a) reaction of magnesium with dilute hydrochloric acid.                 (b) Iron with dilute sulphuric acid. (c) Zinc with dilute nitric acid.

a)      Mg+2HCI⟶MgCI₂+H₂↑

b)      Fe+ H₂SO₄⟶FeSO₄+ H₂↑

c)       Zn+2HNO₃⟶Zn (NO₃)₂+H₂↑

26.          Under what conditions do the following react with water (a) magnesium (b) zinc? Write the chemical equations?

a)      Both magnesium and zinc react with water when

·         The metal is hot

·         Steam is passed over them

b)      Magnesium reacts with steam to give magnesium oxide liberating hydrogen

                Mg+H₂0⟶MgO+H₂↑

c)       Zinc reacts with steam to give zinc oxide liberating hydrogen

                Zn+H₂0⟶ZnO+H₂↑

27.          Explain briefly an experiment to demonstrate the reaction of a metal with different components of air?

·         Cut a small piece of sodium and place it on a watch glass

·         The interior surface of the metal that is shining becomes slowly dull forming sodium oxide

·         4Na+O₂⟶2Na₂O

·         Further, sodium oxide reacts with carbon dioxide to form sodium carbonate.

_·          Na₂O+CO₂⟶Na₂CO₃

·         Thus sodium oxide reacts with air to form sodium oxide first and subsequently sodium carbonate.

28.          Name the mineral acid. How do metals react with them? Give one example each?

·         Hydrochloric acid, sulphuric acid and nitric acid are mineral acids.

·         Metals react with dilute hydrochloric acid to form respective chlorides liberating hydrogen

                Mg+2HCI⟶MgCI₂+H₂↑

·         Metals react with dilute sulphuric acid to form respective sulphates liberating hydrogen

                Mg+ H₂SO₄⟶MgSO₄+ H₂↑

·         Metals react with very dilute nitric acid to form respective nitrates liberating hydrogen

                Mg+HNO₃⟶Mg (NO₃)₂+H₂↑

29.          Name the most commonly used ore for extracting copper. Describe the process of extraction in brief?

a)      Copper is extracted from its sulphides ore copper pyrites.

b)      Following are the steps involved in the extraction.

·         Concentration of the ore:

This is done by froth floatation. The finely powdered ore is mixed with pine oil and water in a large tank.

The water in the tank is agitated by blowing in air due to which froth is formed. The sulphide ore mixes with the oil and forms a thin film and the remaining particles get wetted by water and remain at the bottom.

When air is babbled through this froth particles containing the copper particles floats on the top of water and are skimmed off. Foam settles down and concentrated sulphides ore is obtained.

·         Roasting of the ore:

                The concentrated ore is roasted in air in a blast furnace. It reacts with oxygen to form copper sulphide and ferrous                 oxide

                2CuFeS₂+4O₂⟶Cu₂S+2FeO+3SO₂↑

The product is mixed with sand and heated in a furnace. Ferrous oxide forms ferrous silicate, which is removed as slag. The remaining copper sulphides is further roasted to form cuprous oxide.

FeO+SiO₂⟶FeSiO₃

2Cu₂S+3O₂ ⟶2Cu₂O+2SO₂

Supply of air is stopped. Remaining cuprous sulphides reacts with cuprous oxide and forms molten copper.

Cu₂S+2Cu₂O⟶6CU+SO₂↑

This molten copper is allowed to cool and purified to get pure copper.

30.          What is electrolytic refining? Describe the electronic refining of copper?

a)      The process of obtaining a metal of very high purity from a sample of impure metal by the process of electrolysis is called electrolytic refining.

b)      The electrolytic refining of impure copper is carried out in an electrolytic tank containing acidified copper sulphate solution as the electrolyte.

·         A thick block of impure metal is made the anode and a thin strip of pure copper is made the cathode.

·         Both the cathode and the anode are immersed in the acidified copper sulphate solution

·         On passing electric current, impure copper from the anode dissolves and goes into copper sulphate solution and pure copper from the solution deposits on the cathode.

·         The impurities collect below the anode as anode mud.

31.          Explain the process of extracting iron in brief?

a)      Iron is extracted from its oxide ore haematite. It is composed mainly of ferric oxide and silica.

b)      Following are the important steps involved.

·         Concentration: The ore is concentrated by hydraulic washing. The crushed ore is washed with a stream of water. Heavier particles settle at the bottom, while the lighter gangue is washed away.

·         Roasting: the concentrated ore is mixed with limestone and coke in the ratio 8:1:4 and is introduced into a furnace through the cup and cone arrangement at the top of the furnace.

                Hot air is blown from the bottom of the furnace.

·         Lima decomposes to form calcium oxide and carbon dioxide and further forms calcium silicate.

·         Carbon dioxide is reduced to carbon monoxide which reduces iron oxide to iron and the molten iron is collected at the bottom of the furnace as pig iron or cast iron.

32.          Write the important reactions that take place in the extraction of iron?

                Following reactions take place.

·         Due to the intense heat limestone is decomposed into calcium oxide and carbon dioxide.

                CaCO₃⟶CaO+CO₂

·         Calcium oxide formed during the reaction reacts with silicon dioxide present in the ore as impurity to form molten calcium silicate.

                CaO+SiO₂⟶CaSiO₃

·         Coke combines reacts with oxygen to form carbon dioxide.

                C+O₂⟶CO₂+Heat

·         Carbon dioxide reacts with more coke to form carbon monoxide.

                CO₂(g)+C(s)⟶2CO(g)

·         Carbon monoxide reduces iron (׀׀׀) oxide to liquid iron. The molten iron collects at the bottom of the furnace.

                Fe₂O₃+3CO⟶2Fe+3CO₂

33.          Explain the method of concentration of copper ore?

·         Copper is concentrated by froth floatation.

·         The finely powered ore is mixed with pine oil and water in a large tank.

·         The water in the tank is agitated by blowing in air due to which froth is formed.

·         The sulphide ore mixes with the oil and forms a thin film and the remaining particles get wetted by water and remains at the bottom.

·         When air is bubbled through this, froth particles containing the copper particles floats on the top of water and is skimmed off.

·         Foam settles down and concentrated sulphide ore is obtained.

34.          How does iron react with water? Write the chemical equation?

a)      Iron does not react with cold water.

b)      When steam is passed over hot iron, hydrogen gas is liberated and ferric oxide is formed.

                3Fe+4H₂O⟶Fe₃O₄+4H₂↑

35.          How do the products differ when copper reacts with moderately concentrated nitric acid and concentrated                 nitric acid? Write the balanced chemical equations?

a)      In both the cases cupric nitrate and water are formed. With moderately concentrated nitric acid copper liberates nitric oxide, where with concentrated nitric acid, copper gives nitrogen dioxide.

b)      With moderately concentrated nitric acid the reaction is as follows

3Cu+8HNO₃⟶3Cu (NO₃)₂+2NO+4H₂O

With concentrated nitric acid the reaction is as follows

Cu+4HNO₃⟶Cu (NO₃)₂+2NO↑+2H₂O