CBSE Set Qa2 Science Class X 1996 Sample Test Papers For Class 10th for students online

Science Class X (CBSE)
You are on Answers 22 - 33

Q22. Why does the iron present in the inner core of the earth remain in solid form despite high Temperature ? How does our earth act like an engine ?
Ans22. Because of the high pressure at the inner core iron remains in the solid form despite the high temperature. The outward flow of energy from the hot interior to the cooler surface of the earth makes it behave as an engine.

Q23. An electric meter shows the consumption of one unit of electrical energy for heating 20 kg of water. What would be the rise in temperature of water if the entire electrical energy is used only to heat the water ? (Specific heat of water = 4200 J/kg/°C)
Ans23. given,
mass of water to be heated,m = 20 kg
Specific heat of water = 4200 J/kg°C
energy consumed = 1 unit = 1000 kWh = 3600,000 J
Say, rise in temperature = t °C

Q = m x s x t
            Q
t °C
         m x s

   3600,000

   20 x 4200

= 42.857 = 42.86 °C
Ans: the rise in temperature of water will be 42.86 °C

Q24. What are enzymes? Name its substituents. How are some fruits affected by the action of enzymes. Give one method to reduce the activity of enzymes on fruits.
Ans24. Enzymes are biological catalysts. They consist of proteins. They speed up and regulate many chemical reactions in living cells which are essential for their survival and growth. Even after a part of the plant or animal has been separated from it, enzymes continue to work, driving chemical reactions whose products may be unpalatable or even dangerous. They are thus continuously at work in fruits, until they are consumed or cooked. Over-ripening and spoilage of fruits is often due to enzymes. Keeping fruits at temperatures lower than the temperature required by enzymes (refrigeration) reduces the activity of enzymes on fruits.

Q25. With the help of a labelled diagram and necessary chemical equations describe the preparation of methane in the laboratory.
Ans25. Methane is prepared by heating the mixture of sodium acetate and soda lime. Soda lime is a mixture of sodium hydroxide and calcium oxide.The gas is collected by downward displacement of water.
CH₃COONa + NaOH CH₄ + Na₂CO₃



Q26. We do not consume harmful chemicals as such, then how do they enter our body? Which of the two persons is likely to have more concentration of harmful chemicals-a vegetarian or a non-vegetarian? Give reasons.
Ans26. The harmful chemicals enter in our body through:
Food:
(a) Vegetarian food: A lot of toxic pesticides, weedicides, and fertilizers are used to increases the yield of food crops. These toxic and harmful chemicals enter in our body through the produce of such crops.
(b) Non-vegetarian food: The toxic chemicals get accumulated in the bodies of poultry, fish, and other sources of non-vegetarian food for animals by bio-accumulation. When such non -vegetarian food is eaten, it causes intake of same toxic chemicals in the human body too.

Water: The drainage, seawage and environmental effluents get added in the source of ground and run-off water and cause entry of those toxic chemicals in the human body as well.
Air: The air which we inhale has load of toxic pollutants released by industrial activities. It causes those toxic chemicals to get into human bodies as well.

A non-vegetarian will have more concentration of harmful chemicals because the toxic chemicals get bio-magnified along the food chain:

plants Primary Consumers Secondary Consumers Man

Q27. Why is replenishment of soil essential? Describe two natural ways of soil replenishment.
Ans27. Replenishment of soil is essential because year-by-year cultivation of same crops causes the nutrients depleated away from the soil, and makes the soil deficient in those nutrients leading to lower crop yield in the subseQnt years. By natural means, the soil can be replenished by:
1. Crop rotation: Different crops have different requirements of nutrients in the soil. Rotating the crops under cultivation in a field will ensure that the utilization of all minerals will be uniform. Rotating leguminous crops with non-leguminous crops will ensure that the nitrogenous nutrients depleated from the soil by the non-leguminous crop get replenished by the nitrogen-fixing leguminous crop.

2. To leave the land fallow: Leaving the land fallow for a season helps the soil to make up for the lost nutrients.

Q28. Distinguish between dry heating and wet heating foodgrains. Write two harmful effects of wet heating.
Ans28. Dry heating is the rise in temperature due to the energy released by the respiration of multiplying insects resident in food-grains.
Wet or Damp heating of grains is the rise in the temperature due to the growth of moulds.

Wet heating causes rise in the temperature and the moisture content of the grains, which:
(i) adversely affects the future germination of seeds, and
(ii) reduces the quality of foodgrains.

Q29. Name the three characteristics which describe the orbit of an artificial satellite around the earth. Illustrate them on a diagram. When is a satellite said to be in geostationary orbit?
Ans29. The three characteristics which describe the orbit of an artificial satallite are: 1. Perigee
2. Apogee
3. Inclination


A satallite is said to be Geostationary when with respect to a place on the earth, its position in the space is fixed. This is achieved by keeping the period of rotation synchronous with the revolution time of the earth, that is, 24 hours.

Q30. How is energy liberated in the Sun ? What would happen when all the hydrogen in the Sun gets consumed ? Describe the two steps involved.

Ans30. The source of energy in the sun is the process of Nuclear Fusion.
Two very fast moving nuclei of the heavier isotope of hydrogen, Deuterium collide in the sun's interior to produce helium. This fusion of the nuclei liberates a lot of energy which fires up the sun.

As the H-2 (deuterium) in the Sun's core is used up, the fusion reaction stops there, but it still continues in the outer shell. The core gets the pressure lowered and it contracts under its own gravity. The burning shell expands, increasing its surface area and reduces the intensity of
radiated energy. At this stage, the star A enters the Red Giant phase.

Latter the red-giant star will lose its expanding outershell.The core of red giant star left behind would gradually condense into an exremely dense ball of matter. Due to the contraction of condensation, high temperature would be produced in the core. At this high temperature Helium present in the core would fuse to form higher elements like carbon and liberate a lot of energy. The energy liberated by these fusion reactions cause the small core glow as White Dwarf Star until helium lasts into it.

Q31. What is a balanced diet? How does the balanced diet depend on special needs? Explain with the help of two examples. Why the roughage and water are important part of balanced diet. Name two sources of roughage in our diet.
Ans31. Balanced diet is a food which contains the requisite amount of food nutrients - Carbohydrates, proteins, fats, vitamins, minerals, water, and roughage.

The balanced diet depends on the physical and the biological needs of the individual.
#1 A growing-up child will need more carbohydrates and proteins, than an old-aged man.
#2 The pregnant woman has higher requirements of milk, and minerals.
Also a person doing a lot of physical labour will have a different requirement of nutrients than that of some one with a sedentary life style.

Roughage and water help in the proper digestion of the food and in the bowel movement. Water is important as a solvent, temperature regulator, means of excretion, and a medium of biological reactions.
Roughage make the bulk of the diet, and the feces.

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Two sources of roughage in our food are:
1. Fibres in fresh vegetables, and fruits
2. Fibres in unprocessed grains


Q32. With the help of labelled diagrams, explain the construction and working of a diesel engine. State any two differences between a petrol engine and a diesel engine.
Ans32. The working of a diesel engine can be divided into four stages (strokes):

(i) The Intake Stroke
# the diesel engine starts
# the piston P moves downwards in the cylinder
# a region of low pressure is created in the upper part of the cylinder
# the intake valve V₁ opens up
# air enters into the cylinder

(ii) The Compression Stroke
# when a sufficient amount of air has entered the cylinder the intake valve V₁ gets closed
# the piston is forced to move upwards
# the air present in the cylinder gets compressed excessively
# compression produces heat
# the air present in the cylinder becomes very hot

(iii) Expansion Stroke (or Power Stroke)
# having compressed the air, piston P reaches the upper part of the cylinder
# a fine spray of diesel oil is injected into the cylinder through the nozzle N
# due to the high temperature of air in the cylinder, diesel oil burns immediately
# the burning of diesel fuel produces large quantities of gases like CO, CO₂, H₂O
# a large amount of heat is also produced
# due to excessive heat, these gases expand rapidly
# the pressure of rapidly expanding hot gases pushes the piston downwards with a great force
# the moving piston pushes its piston rod R
# the piston rod in turn pushes the crank-shaft
# the crank-shaft turns the motor wheel

(iv) Exhaust Stroke
# the piston has been pushed to the bottom of the cylinder by the hot expanding gases in the expansion stroke
# the exhaust valve V₂ opens up
# due to the momentum of the rotating wheels of the vehicle, the piston is pushed upwards
# when the piston moves upwards, it expels the spent cold gases from the cylinder through the exhaust valve V₂.
# the exhaust valve V₂ gets closed,

the intake valve V₁ opens up again and the above four strokes of the diesel engine are repeated again and again.

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Charging Compression Working Exhaust

Difference between Petrol and Diesel Engine

Q33. Name the chief ore of iron. What are the three raw materials used in the production of iron from its ore? With the help of a labelled diagram of a blast furance, describe the extraction of iron from its ore. Write the chemical equations of the reactions involved
in the furnace.
Ans33. Chief ore of iron is Red Haematite (Fe₂O₃₎, which has sand (SiO₂) as the main impurity in it. The three raw material used in the extraction of iron from Haematite are:
1. Coke,
2. Air blast,
3. Lime Stone (CaCO₃)

Iron ore, limestone, and coke are put together in a big Blast furnace.
The blast furnace is smaller at bottom, widens out in the middle and again narrows down at the top. Blasts of preheated air are forced in from the bottom of the furnace, and the exhaust gases escape out from the top. Powdered charge (Ore + limestone + coke) is fed from the top of the
furnace.

Fig.:- Blast Furnance
Limestone gets dissociated because of intense heat in the furnace:
CaCO₃ CaO + CO₂
Calcium oxide reacts with sand to form calcium silicate:
CaO + SiO₂ CaSiO₃
Iron oxide thus freed from sand gets reduced by the help of carbon monooxide:
2 C + O₂ 2 CO
Fe2O3 + 3CO 2 Fe + 3 CO₂
The calcium silicate formed keeps the freshly formed iron away from oxygen. Calcium silicate being lighter than molten iron floats on the surface, and is separated as scum.