CBSE ANNUAL PAPER - 1999

SCIENCE (THEORY)

(SET-I)

Time Allowed : 3 Hours

Maximum Marks : 75

General Instructions :

(i) All questions are compulsory.

(ii) Marks for each question are indicated against it.

(iii) Question numbers 1 to 10 are very short answer type questions, carrying 1 mark each to be answered in one word or maximum in one sentence.

(iv) Question numbers 11 to 20 are short answer type questions. Carrying 2 marks. answer may not normally exceed 40 words each.

(v) Question numbers 21 to 30 are short answer type questions of 3 marks each. Answer may not normally exceed 60 words each.

(vi) Questions numbers 31 to 33 are long answer type questions, carrying 5 marks each, which should not be answered in more than 100 words each.

(vii) Please write down the serial number of the question before attempting it.

Name the orbit of the satellites that help in satellite communication.

A torch cell converts one form of energy into another form. Name these two forms.

Name the process that forms the basis of a hydrogen bomb.

How does the conductivity of a semi - conductor change when certain impurities are added to it?

Conductivity, that is ability to conduct electricity, or a semi conductor increases considerably when certain impurities are added to it.

Common salt contains some amount of MgCl₂(Magnesium Chloride) which absorbs moisture from air in rainy season, when air has the maximum moisture in it, and becomes moist.

Which property of diamond makes it a suitable material for high precision thermometers ?

Name the Vitamin which gets oxidised when cut fruits are left exposed to air for a long time.

In a good chain comprising lion, grass and dear, which will (i) transfer the maximum amount of energy (ii) receive minimum amount of energy.

(ii) Minimum amount of energy will be received by lion.

Vinegar in water, Aluminum paints, Blood, Muddy water.

The lungs perform 2.4 J of work during each expansion. How many times per minute do they expand if their power is 2 watts ?

Power of lungs = 2 w

Power = Work / Time

Time = Work / Power

Time taken by lungs in expansion = 2.4 2.4 J /2 W = 1.2 Sec.

NO. of expansions in 1 min. or 60 sec.

= 60/1.2 = 50 Expan.

Cadmium rods play an important role in a nuclear reactor. What happens (i) When they are completely inserted into nuclear fuel, and (ii) when they are slowly withdrawn from nuclear fuel.

(i) Nuclear fission is stopped when the cadmium rods are completely inserted into the nuclear fuel as the cadmium rods absorb all the neutrons responsible for fission reaction.

(ii) When cadmium rods are withdrawn slowly from the nuclear fuel, the fission of nuclear fuel starts and goes on increasing as the rods are withdrawn because neutrons will be available for fission reaction.

A compound which is prepared from gypsum has the property of hardening when mixed with proper quantity or water. Identify the compound. Write the chemical equation of its preparation. Mention one important use of the compound.

Preparation - It is prepared by heating gypsum.

Use - It is used in surgery to maintain joints in a fixed position.

Which category of compounds is formed when one hydrogen atom of an alkane molelcule is replaced by a hydroxy1 group ? Name the functional groups is the following compounds.

'Alcohol' is formed when one hydrogen atom an alkane molecule is replaced by a hydroxyl group (-OH).

O O
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(i) In compound R - C - OH - C - OH. or - COOH is the functional group naming Carboxyl group.

O O

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(ii) In compound R - C - O - R', - C - O or - COO. is the functional group naming ester group.

How is the polar nature of water responsible for dissolving (i) Sodium chloride (ii) Sugar ?

Polar Nature of water - Water molecule is made up of one oxygen atom and two hydrogen atoms. Oxygen atom end has some negative charge (d ^- ) while hydrogen atoms end has some positive charge (d ⁺ ) thus water molecule has two ends with different charges.

(ii) Sodium Chloride is an electrovalent compound and Na⁺ and CL ions attach with both ends of unlike charged ends of water molecule resulting the Nacl be dissolved in water due to weakening of ionic bond.

(iii) Sugar is a covalent compound. Hydrogen atoms of water molecule can chemically bind loosely with the strongly electro negative atoms of covalent compound by hydrogen bonds and thus sugar is dissolved in water.

Give an example of a food chain consisting of four organisms at different trophic levels. Give the scientific term used to indicate the first and third trophic level.

Grain plants ---- Rat --- Snake ---- kite

I II III IV

First trophic level - At first trophic level grain plants are present which synthesise the fod and trap solar energy. Organisms at this level are called producer.

Second Trophic level - Organisms present at IInd trophic level is Rat which feed on grain plants i.e. rat gets its food from plants so, it is called herbivore or first consumer.

Third trophic level - Snake is present at IIIrd trophic level which is IInd consumer and consumers rat as food. Organisms at this level are called carnivores.

What is biological fixation ? How is it different from nitrification ? Give an example of organism involved in each of these.

Biological Fixation - The conversion of nitrogen gas of the atmosphere into nitrogen compound nitrates, easily usable form of nitrogen for plants by the action of bacteria and algae, is called biological fixation. e.g. Rhizobium bacteria present in root nodules of leguminous plants.

Nitrification - It is one step of nitrogen cycle in nature. In this step ammonia is converted first into nitrites and then in nitrates.

Nitrosomonas - bacteria convert ammonia into nitrites.

Nitrobacter - bacteria convert nitrites into nitrates. These two bacteria are called nitrifying bacteria.

Differentiate between arithmatic progression and geometric progression in terms of food and population.

1. Food Production - Food production increases in arithmatic progression. In arithmatic progression the factor simply add up, so the increase is less.

Food Production - (i) Arithmatic progression - 2--4--6--8--10--12--14.....

2. Geometric Progression - In the geometric progression the factor go on multiplying, So the increase is very rapid. Population increases in geometrical progression.

(ii) Population --2--4---8--16---32--64.....

(Geometric Progression )

What is immunity ? Name the diseases against which DPT vaccine acts as a preventive measure.

Immunity - The resistance power of the body against diseases is called immunity, it is natural and created (artificial) . D.P.T. Vaccine prevents the body against following three diseases.

D - Diphtheria

P- Pertusis ( whooping cough)

T-Tetanus.

A 100 watt electric bulb is lighted for 2 hours every day and five 40 watt tubes are lighted for four every day. Calculate (i) the energy consumed for 60 days and (ii) the cost of electricity consumed at the rate of Rs. 1.50 per K.wh.

Time of use = 2 hours perday

Electricity consumed by bulb perday = 100X2 / 1000 kwh.

Electricity consumed by bulb in 60 days = 100 X 2 / 1000 X 60 /1 KWh = 12 Kwh

Power of tube = 40 w

Time of use = 4 hr.

Electricity consumed by 5 tubes per day = 40 X 5 X 4 /1000 kwh

Electricity consumed by 5 tubes in 60 days = 40 X 5 X 4 / 1000 X 60/1 Kwh = 48 kwh

Total consumption of electricity in 60 days = 12+48 = 60 kwh

Cost = 60 x 15 = Rs. 90.00

Describe the sequence of changes that would take place if all the hydrogen present in the sun is converted to helium.

If all the hydrogen of the sun converts into helium then the following changes will occur.

(i) The fusion reaction in the core would stop and pressure in core would drop which would make the sun core begin to contract under its own gravity.

(ii) In the outer shall hydrogen would continue to fuse and will liberate energy. The shell would begin expand, increasing its surface area. Intensity of radiated energy would also be reduced, its colour would begin to appear red. This stage is called Red Giant phase.

(iii) It outer shell would continue expanding and would engulf the sun's planets, ultimately its expanding shall would be lost.

(iv) Its cost left behind would gradually condense into an extremely dense ball of matter. Due to high temperature and pressure helium of its core would begin fuse into higher elements like carbon. The energy liberated thus make the core to glow. This glowing core is called white Dwarf Star. As long as helium lasts the core would convert into a dense lump.

Mass of the earth is optimum to facilitate existence of life on it. What would have happened if the earth had less mass than at present.

Mass of the earth is optimum to facilitate existence of life on it. If the mass of earth had less than at present then the following happenings could be happened.

(i) It would have contained less amount of radio active elements which in turn would have produced less heat which could not be able for differentiation of earth and no atmosphere would had formed.

(ii) The earth kiln would not have fired to release water vapours from hydrated minerals hence formation of oceans - the bed for originating primitive life, could not be happened.

(iii) The core and mantle would not have formed which release energy and which make the earth dynamic through volcano eruptions, earthquakes, formation of new rocks etc.

List the characteristics which define the orbit of a satellite. Show their position in a diagram. When is a satellite is said to be in a sun synchronous orbit ?

To define an orbit of earth a satellite following characteristics are taken in to consideration :

1. Apogee : It is the farthest point on orbit of a satellite from the earth.

2. Perigee : It is the nearest point on the orbit of a satellite from the earth.

3. Angle of Inclination : It is the angle of inclination of an orbit i.e. the angle between orbit and the equator.

Sun synchronous orbit - When the orbit of a satellite is such that the satellite passes over a particular latitude at approximately the same local time. In other words, the position of the sun with respect to a point on earth remains approximately the same as the satellite passes over it. OR we can say that the satellite in this orbit always laces the sun.

Name the main constituents of liquefied petroleum gas. Why is this gas considered a better domestic fuel than others ? (Give any four points) Give the calorific value of LPG.

The main constituents of LPG are butane, isooctane, propane and a very small amount of ethane.

LPG is an ideal fuel because - (i) IT has high calorific value i.e. approximately 55 KJ/g.

(ii) It's ogmotopm temperature is proper.

(iii) It does not produces smoke, harmful gases on burning i.e. does not produce pollution.

(iv) It does not leave solid residue behind as ash.

(v) It does not blaken the utensils.

(vi) It's combustion is regualr and moderate.

(vii) It's transportation and storage is easy.

Calorific value of LPG is 55 K.J./g.

Explain how the following metals are obtained from their compounds by the reduction process.

(a) Metal X which is low in the reactivity series.

(b) Metal Y which is in the middle of the series.

(c) Metal Z which is high up in the reactivity series.

(a) Metal X - Metal ! x is low in the reactivity series i.e. it is very less reactive metal, so it can be obtained by direct heating in air.

(b) Metal Y - Metal Y is the middle of the series, it an be obtained by heating with a reducing agent like carbon or highly reactive metals like Na, Ca, Al.

(c) Metal Z - Metal Z is high up in the reactivity series. It can be obtained by electrolytic reduction.

What are thermosetting polymers ? Give two examples. Why can they be not processed again ?

Thermosetting plastics : It is the plastic which do not soften on heating and can not be remolded on heating in the desired shape.

Example : Bakelite, Melamine.

Can't be processed again - Thermosetting plastics are the polymers which contain long chain of monomers which are cross linked with each other.This linkage prevents the displacement of individual chain on being heated. Thus thermosetting plastics do not suffer change in shape once they have been set.

Describe with the help of a flow diagram the transfer of energy from sun to top carnivores.

The source of energy on earth is the only sun. Only green plants are capable to trap the solar energy coming on earth. Only 1 % of the total coming energy in trapped by the green plants during photosynthesis and converted into chemical energy started in the food while the rest of the energy is radiated back into the environment.

At each tropic level 10 % of the obtained energy is passed on to the next. Tropic level and 90 % of that obtained energy is utilized at that very level. This utilized energy is lost to environment in the form of heat energy during its metabolic activities. In this way it goes on decreasing at each level and as result very less energy is obtained by the last tropic level. Suppose 1000 J of energy comes to earth then how much energy will be available at different tropic levels of a food chain, has been shown in the following diagram :

A doctor examined a child below the age of five years and found cracks and scaly skin apart from wasting of muscles. Name the disease the child is suffering from. Mention two causes of it s occurrence. What diet should be given to over come this disease.

The symptoms, (i) cracks and scaly skin (ii) loss of muscles in a child below the age of 5 years, are the symptoms of Marasmus.

causes of marasmus -

(i) Weanation of children from Protein in rich breast milk.

(ii) Diet of child deficient in proteins and carbohydrates due to poverty or lack of education.

Remedies - (i) By giving a sufficient protein and carbohydrates rich diet such as a combination of wheat, gram, peanuts, soyabean and jaggery.

(ii) The diet should contain animal protein. Child should be given a sufficient amount of milk, curd, egg or cheese with carbohydrates.

Distinguish between bactericidal and bacteriostatic methods of food preservation. Give one example each of a food material preserved by these methods.

Bactericidal Method : In bactericidal method food is preserved by killing the bacteria ( microbes).

Example : Canning, cooking are the bactericidal methods. jam, jelly boiling of milk are the food material preserved by this method.

Bacteriostatic Method :- In bacteriostatic method food is preserved by checking the actives of bacteria, enzymes. In this method enzyme and microbes are made inactive or is stopped their growth.

Example : Dehydration, salting, pickling etc. are the bacteriostatic methods. Mango pickle, Murata, Leafy vegetables are preserved by this method.

Explain the working of four - stroke engine using petrol as fuel. Draw a neat labeled diagram of the ignition stage.

Working : Its working can be explained with the help of five following stages of its working :

(a) Intake Stroke : As shown in the fig (a) piston moves outward the mixture of fuel and air enters the cylinder through in-take value.

(b) Compression : Now piston moves inside and the fuel + air mixture is compressed, as shown in fig.

(c) Ignition : As the mixture of fuel and air is compressed fully, the spark plug produces an electric spark which ignites the fuel.

(d) Expansion : Hot vapours of gases on ignition expand and push the piston outside which make the crank to move. This is power stroke of the engine.

(e) Exhaust :- In this stroke burnt gases as smoke is exhausted through exhaust value.

Name the chief impurity present in iron ore. What are the two requirements to obtain iron from its ore. Draw a labelled diagram of a blast furnace. State the main reactions that take place in the blast finance. Write the chemical equations involved.

The chief impurity - Sand i.e. silicon dioxide (SiO₂ ) is the chief impurity present in iron ore.

Requirement - (i) A suitable reducing agent to reduce iron oxide to iron. Carbon monoxide (CO) is the reducing agent which is obtained by burning of coke in an insufficient supply of air in the blast furnace.

(ii) Suitable solvent to dissolve ( remove ) silicon dioxide (sand). Silicon dioxide is separated using molten calcium oxide(CaO). It is obtained by heating of lime stone CaCo₃) in the best furnace.

Ore : Most of the iron is obtained from the ore Hematite and magnetite which are iron oxides. (Fe₂O₃)

Structure of furnace : It is a big furnace smaller at the bottom, widens in the middle and again narrow at the top. Finely frinded concentrated ore, sand (SiO₂) lime stone (CaCo₃) and coke is mixed together and furnace is charged by this mixture from the top in a regulated manner. Once started the furnace can continue up to 5 years.

Process : Process is completed in to following steps :

(I) Lime stone (CaCo₃ ) dissociate because of intense heat in the furnace.

CaCO3 --------------- CaO + CO2

(ii) Thus formed CaO removes the sand in the form of calcium silicate which floats over the molten iron at the bottom of the furnace.

CaO = Sio2 -- CaSiO3

Calcium Silicate (slag)

(iii) Reduction of iron oxide occurs by the CO formed by heating of coke in insufficient supply of oxygen. Thus molten iron is obtained at the bottom of the furnace.

2C + O2 ---------------- 2CO

Fe2O3 + 3CO --- 3CO2 + 2Fe.

Role of Slag or Calcium silicate : Lime stone dissociates in to Cao which remove sand in the form of ( Calcium silicate). It is interesting to note that formation of calcium silicate not only removes the sand rather protects the molten iron from oxygen and avoid further oxidation of molten iron.

Place of iron Extraction in India : Jamshedpur, Rourkela, Bhilai, Durgapur.

Which nutrient serves as a ready source of energy in our body ? Write its chemical formula Write down the balanced equation for its complete oxidation . What test will you perform for its presence in a food sample ? Where is this nutrient stored in the body when present in excess ?

Nutrient -Glucose is the nutrient which serves as a ready source of energy in our body.

Test for Glucose - Take some pieces of the given food sample and crush them. Add few drops of Benedict's solution to the crushed food sample in a test tube and heat it. If the colour changes to red it shows the presence of glucoose in the given food sample.

Storage of Glucose in the body - Excess amount of glucose is stored in the liver in the form of Glycogen . Excess amount of glucose is converted by Insulin Harmone - secreted by pancreas, into glycogen and slycogen stored in the liver is utilised by the body later on for the production of energy for body activities when ever we are on fast.