Set-2

CBSE 2009 Science X (SET 2) SCIENCE (Theory)

Time allowed: 2

1 hours 2

Maximum Marks: 60

General Instructions: (i)

The question paper comprises of two sections, A and B. You are to attempt both the sections.

(ii)

All questions are compulsory.

(iii)

There is no overall choice. However, internal choice has been provided in all the three questions of five marks category. Only one option in such questions is to be attempted.

(iv)

All questions of Section A and all questions of Section B are to be attempted separately.

(v)

Questions number 1 to 6 in Section A and 17 to 19 in Section B are short answer type questions. These questions carry one mark each.

(vi)

Questions number 7 to 10 in Section A and 20 to 24 in Section B are short answer type questions and carry two marks each.

(vii)

Questions number 11 to 14 in Section A and 25 and 26 in Section B are also short answer type questions and carry three marks each.

(viii)

Questions number 15 and 16 in section A and question number 27 in section B are long answer type questions and carry five marks each.

CBSE 2009 Science X (SET 2) Section A 1. What happens when a small piece of sodium is dropped into ethanol? Answer: When a small piece of sodium is dropped into ethanol, sodium reacts with ethanol to give sodium ethoxide. Hydrogen gas is evolved in the process. This reaction can be represented by the following equation. 2Na

2CH3CH 2 O Na + +

+ 2CH3CH 2 OH

Sodium

Ethanol

Sodium ethoxide

H2 Hydrogen

2. Which one of these has a higher concentration of H+ ions? 1 M HCl or 1 M CH3COOH Answer: HCl is a stronger acid than CH3COOH. When added to water, HCl dissociates almost completely to give H+ ions. In contrast, in the case of CH3COOH, only partial ionisation occurs. This is why 1 M HCl solution has a higher concentration of H+ ions than 1 M CH3COOH solution.

3. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas collected over the other electrode? Answer: The balanced chemical equation for the electrolysis of water is: 2 H 2O (l ) Water

Electricity H2SO4

2 H 2 (g ) Hydrogen

O2 ( g ) Oxygen

It can be observed from the balanced chemical equation that the volumes of hydrogen and oxygen produced during electrolysis are in the ratio 2: 1. Thus, the volume of hydrogen gas collected in the process is double than that of oxygen. 4. State the rule which gives the direction of magnetic field associated with a current-carrying conductor.

CBSE 2009 Science X (SET 2) Answer: The direction of the magnetic field produced around a current-carrying conductor is determined by the right-hand thumb rule. According to this rule: If one holds a current-carrying conductor with the right hand, such that the thumb points in the direction of the current flowing through the conductor, then the other fingers will wrap around the conductor in the direction of the field lines of the magnetic field due to the conductor.

5. Define the term ‘induced current’. Answer: If a conducting wire is placed in a changing magnetic field or if a conducting wire moves in a magnetic field, then a current is generated in the conducting wire. This electric current generated in the conducting wire because of changing magnetic field is known as induced current.

6. Draw a schematic diagram of an electric circuit consisting of a battery of two cells each of 1.5 V, 5 , 10 and 15 resistors and a plug key, all connected in series. Answer: The emf of each cell is 1.5 V. When the two cells are connected in series, the emf of the battery becomes (1.5 + 1.5) V = 3 V. Therefore, the schematic diagram of the series circuit is as follows:

7. Crystals of copper sulphate are heated in a test tube for some time (a)

What is the colour of copper sulphate crystals (i) before heating, and

CBSE 2009 Science X (SET 2) (ii) after heating? b)

What is the source of liquid droplets seen on the inner upper side of the test tube during the heating?

Answer: (a)

(i) (ii)

The colour of copper sulphate crystals before heating is blue. The colour of copper sulphate crystals after heating is white.

(b)

The source of liquid droplets seen on the inner upper side of the test tube during heating is the water of crystallisation present in the copper sulphate crystals before heating.

8. (i)

What is observed when a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube?

(ii)

What type of reaction is this?

(iii)

Write a balanced chemical equation to represent the above reaction.

Answer: (i)

When a solution of potassium iodide is added to a solution of lead nitrate taken in a test tube, the precipitation of a yellowish solid is observed. This yellowish solid is lead iodide. Potassium nitrate is formed along with lead iodide.

(ii)

This is a double displacement reaction.

(iii)

The balanced chemical equation for the above reaction is:

2KI(aq ) Potassium iodide

+

Pb(NO3 )2(aq )

2KNO3(aq )

Lead nitrate

Potassium nitrate

+

PbI2(s ) Lead iodide

9. A lamp rated 100 W at 220 V is connected to the mains electric supply. What current is drawn from the supply line if the voltage is 220 V? Answer: The electric power (P) is related to potential difference (V) and current (I) as:

CBSE 2009 Science X (SET 2) P=V×I The power of the lamp, P = 100 W Potential difference across the lamp, V = 220 V Therefore, the current drawn by the lamp from the supply line is: I

P V

100 220

0.45 A

10. What is an electric circuit? Distinguish between an open and a closed circuit. Answer: An electric circuit consists of electric devices (bulb, fan, etc.), switching devices (key, fuse, etc.) and source of electricity (electric cell, battery, etc.). These are connected by conducting wires. An open circuit is an incomplete circuit and current does not flow through it, while a closed circuit is a complete circuit and current flows through it.

11. (a)

What is a homologous series of substances?

(b)

In an organic compound, which parts largely determine its physical and chemical properties?

(c)

Write a chemical equation to represent the reaction of ethanol with acidified solution of potassium dichromate?

Answer: (a)

A homologous series is a series of carbon compounds that have different numbers of carbon atoms, but contain the same functional group. All the functional groups form a homologous series.

(b)

The physical properties of an organic compound are determined by both the number of carbon atoms and the functional group. Its chemical properties are determined only by the functional group.

(c)

Acidified potassium dichromate is a strong oxidising agent. It oxidises ethanol to ethanoic acid.

CH3CH2OH Ethanol

Δ Acidified K2Cr2O7

CH3COOH Ethanoic acid

CBSE 2009 Science X (SET 2) 12. (a)

What is meant by periodicity in properties of elements with reference to the periodic table?

(b)

Why do all the elements of the same group have similar properties?

(c)

How will the tendency to gain electrons change as we go from left to right across a period? Why?

Answer: (a)

The properties of elements are not distinct and recur from time to time. In the periodic table, elements are arranged in such a manner that the elements with similar properties are present in the same group.

(b)

The properties of elements depend upon their electronic configurations. The elements having similar electronic configurations have similar properties. As the elements of the same group have similar electronic configurations, they have similar properties.

(c)

As we move from left to right across a period in the periodic table, the tendency to gain electron increases. On moving from left to right across a period in the periodic table, there is an increase in the nuclear charge of the elements. At the same time, the size of the elements decreases. As a result, the effective nuclear charge acting on the valence electrons increases. Hence, the tendency to gain electrons increases.

13. (a) (b)

Define the term ‘coulomb’. State the relationship between the electric current, the charge moving through a conductor and the time of flow. Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA.

Answer: (a)

Coulomb: Coulomb is the unit of electric charge. The amount of charge that passes through a conductor when 1 ampere current flows through the conductor for 1 second is defined as 1 coulomb. 1C=1A×1s

(b)

If a net charge Q, flows across any cross-section of a conductor in time t, then the current I flowing through the cross-section is:

CBSE 2009 Science X (SET 2) Q t

I

In the given problem: Current flowing through the bulb, I = 200 mA = 0.2 A Time of flow of current, t = 20 min = 1200 s Therefore, Q = I × t = 0.2 × 1200 = 240 C Hence, 240 C charge is passed through the bulb.

14. For which position of the object does a convex lens form a virtual and erect image? Explain with the help of a ray diagram. Answer: When an object is placed between the focus and the optical centre of a convex lens, a virtual and erect image of the object is formed. When the object is placed between the focus F1 and optical centre O: In this case, the image is formed on the same side as the object. This image is virtual, erect, and very large in size. It is formed behind 2F1.

P’Q’ is the image. PQ is the object. F2 is the focus on the other side of the lens.

15. (a)

Distinguish between ionic and covalent compounds under the following properties:

CBSE 2009 Science X (SET 2)

(b)

(i)

Strength of forces between constituent elements

(ii)

Solubility of compounds in water

(iii)

Electrical conduction in substances

Explain how the following metals are obtained from their compounds by the reduction process: (i)

Metal M which is in the middle of the reactivity series.

(ii)

Metal N which is high up in the reactivity series.

Give one example of each type OR (a)

Distinguish between ‘roasting’ and ‘calcination’. Which of these two is used for sulphide ores and why?

(b)

Write a chemical equation to illustrate the use of aluminium for joining cracked railway lines.

(c)

Name the anode, the cathode and the electrolyte used in the electrolytic refining of impure copper.

Answer: (a)

(b)

(i)

The forces of attraction between the constituent elements (positive and negative ions) of ionic compounds are stronger than the forces of attraction between the constituent elements of covalent compounds.

(ii)

Ionic compounds are soluble in polar solvents such as water and are insoluble in non-polar solvents such as petrol, kerosene, etc. Covalent compounds on the other hand dissolve readily in organic solvents such as alcohol and acetone, but are insoluble in polar compounds.

(iii)

Ionic compounds conduct electricity in their molten state or aqueous form, whereas covalent compounds do not conduct electricity.

(i)

Metals that are present at the centre of the reactivity series are moderately-reactive. Therefore, metal M is a moderately-reactive metal. After obtaining the metal oxides from ores, the metal oxides are reduced to obtain the pure metals. As metal M is a moderately reactive metal, its oxide can be reduced by using coke (carbon).

CBSE 2009 Science X (SET 2) Metal oxide + Carbon

Metal + Carbon monoxide

One example of metal M: Iron (Fe) (ii)

Metals that are present higher up in the reactivity series are very reactive metals. Hence, metal N is a highly reactive metal. Oxides of highly reactive metals cannot be reduced by using coke. Therefore, these metals are reduced by passing electric current through their molten salts. This process is known as electrolytic reduction. One example of metal N: Sodium (Na) OR

(a)

Roasting involves the strong heating of an ore in the presence of an excess of air. On the other hand, calcination involves the strong heating of an ore in the absence of air. Among these two, the process that is used for sulphide ores is roasting. This is because on roasting, metals sulphides get converted into metal oxides. This is done because the reduction of oxides is comparatively easier than the reduction of sulphides.

(b)

Aluminium is more reactive than iron and can be used for reducing iron oxide to iron. The equation for the same is: Fe2O3 (s)

2Al (s)

Iron (III)oxide

Aluminium

2Fe (l ) Iron

Al2 O3 (s)

Heat

Aluminium oxide

The iron produced in this reaction is in liquid (molten) state as this reaction is highly exothermic. This reaction is known as ‘thermit reaction’ and is used for joining and repairing railway tracks or broken pieces of iron in heavy machines. (c)

A large block of impure metal (copper) is made the anode and a thin strip of pure metal (copper) is made the cathode. An acidified solution of copper sulphate (CuSO4) is taken as the electrolyte.

16. (a)

(b)

What is myopia? State the two causes of myopia. With the help of labelled ray diagram, show (i)

The eye defect myopia

(ii)

Correction of myopia using a lens.

Why is the normal eye unable to focus on an object placed within 10 cm from the eye?

CBSE 2009 Science X (SET 2) OR (a)

What is dispersion of white light. What is the cause of such dispersion. Draw a diagram to show the dispersion of white light by a glass prism.

(b)

A glass prism is able to produce the spectrum when white light passes through it, but a glass slab doesn’t produce any spectrum. Explain why it is so.

Answer (a)

Myopia: It is a defect of vision in which a person cannot see distant objects clearly, but has no problems in seeing nearby objects. Causes of Myopia: (i) Excessive curvature of eye lens (ii) Elongation of the eyeball

(i) Ray diagram of the eye defect myopia

(ii) Ray diagram of the correction of myopia

(b)

For a normal eye, the near point (i.e., the minimum focus distance) of the eye lens is 25 cm. The curvature of the eye lens becomes the maximum (and hence, the focal length becomes the minimum) when an object is placed exactly 25 cm from the eye lens. If an object is placed at a distance of 10 cm (i.e., within the 25 cm distance from the eye lens), then the curvature of the eye lens cannot increase further. Therefore, the focal length of the eye lens does not get adjusted to focus the light rays coming from the object onto the retina. As a result, a blurry image of the object is formed on the retina.

CBSE 2009 Science X (SET 2) OR (a)

Dispersion: The splitting of white light into its seven component colours is called dispersion. Cause of dispersion: Dispersion of white light occurs because of the varying speeds of different coloured lights through different media. White light consists of seven colours. The speeds of these coloured lights are the same through air. However, their speeds vary in other media. Therefore, when white light enters from one media to another, its component colours get refracted by different angles. As a result, dispersion occurs.

Dispersion of white light by a glass prism

(b)

The two faces of a glass prism are at an angle (angle of prism) with each other. Therefore, the angle of incidence and the angle of emergence of a light ray become different in the case of a prism. Therefore, when white light gets dispersed after entering a prism, its component colours spread more after refracting through the opposite face of the prism. In the case of a glass slab, the two opposite faces of the slab are parallel to each other. Therefore, the angle of incidence and the angle of emergence of a light ray remain the same for a glass slab. Therefore, the dispersed light rays combine to form white light after refracting through the second face of the glass slab.

CBSE 2009 Science X (SET 2) Section B

17. Why are green plants called ‘Producers’? Answer: Green plants are called producers as they can synthesise their own food in the presence of sunlight by using simple inorganic raw materials such as carbon dioxide, water and minerals. They are also known as autotrophs.

18. Why is DNA copying an essential part of the process of reproduction? Answer: DNA (Deoxyribonucleic acid) copying is an essential part of reproduction as it passes genetic information from the parents to the offspring. Therefore, it determines the body design of an individual. 19. Which compounds are responsible for the depletion of ozone layer? Answer Chlorofluorocarbons (CFCs) are responsible for the depletion of the ozone layer. 20. Describe how hydro-energy can be converted into electrical energy. Write any two limitations of hydro-energy. Answer: In hydropower plants, a large amount of water is stored at a height. This stored water is then allowed to fall on rotating turbines. The force of the running water (kinetic energy of running water) causes the turbines of the plant to spin. The rotating turbines then spin the generator, which ultimately produces electricity. In this manner, the kinetic energy of the running water is converted into mechanical energy and then finally into electrical energy. Two limitations of hydropower energy Causes a change in the course of rivers and lot of land is submerged under water. Fish and wildlife are affected drastically.

CBSE 2009 Science X (SET 2) 21. How is charcoal obtained from wood? Why is charcoal considered a better fuel than wood? Answer: Charcoal is obtained when wood is heated in the absence of air. This process is known as destructive distillation of wood. Charcoal is considered a better fuel than wood because the former has a better calorific value than wood. Also, charcoal does not produce any smoke when burnt.

22. Describe the role of the following in human beings: (i)

Seminal vesicles

(ii)

Prostate gland

Answer: (i)

Seminal vesicles - The secretions of seminal vesicles contain many proteins and enzymes and thus provide nutrition to the developing sperms.

(ii)

Prostate gland - The prostate gland secretes a slightly alkaline fluid that lubricates the sperms and neutralises the acidity of the vaginal tract.

23. An environmentalist on visit to your school suggested the use of three R’s to save the environment. Explain what he meant by three R’s and how you would follow his advice at home. Answer: The three ‘R’s mentioned by the environmentalist are Reduce, Recycle and Reuse. We can save our environment by practicing these three ‘R’s. (a) Reduce: Reduce means using less. An example of this is reducing the wastage of electricity by switching off lights and fans when not required. (b) Recycle: Recycle means collecting the used and discarded items of paper, plastic, glass materials, and sending them to the respective industries for making fresh paper, plastic, glass or metal objects. One should encourage the use of products made from these recycled materials, instead of using products made from fresh materials.

CBSE 2009 Science X (SET 2) (c) Reuse: Reuse means using the same things again and again. For example, one should reuse packing materials such as the cardboard and thermocol coverings of electronic items.

24. What is Chipko movement? Why should we conserve forests? Answer: The Chipko movement, which originated in Reni, Garhwal, was an agitation of tribal habitants directed against deforestation in the region and their alienation from the forests. We must conserve our forests to preserve biodiversity (range of different life forms) so as to avoid the loss of ecological stability. A large number of tribes live in and around forests. If forests are not conserved effectively, then these tribes may lose their habitat. If forests are not managed properly, then water resources, quality of soil, and even the amount of rainfall in a particular region may get affected. In simple words, without forests, life will become extremely difficult for human beings.

25. Explain how the sex of the child is determined at the time of conception in human beings. Answer: Every somatic (body) cell of humans contains 23 pairs of chromosomes. Out of these 23 pairs, the first 22 pairs (44 chromosomes) do not determine the sex of an individual and they are known as autosomes. The remaining one pair determines the sex of the individual. This last pair is known as the sex chromosomes and are represented as X and Y. The male gametes have 22 autosomes and either an X or a Y sex chromosome. On the other hand, the females have XX sex chromosomes, along with the 22 autosomes. This means that their gametes can only have an X sex chromosome Therefore, the sex of the child is determined by the type of the sperm (containing an X or a Y sex chromosome) which fuses with the egg cell (containing an X chromosome) at the time of conception.

CBSE 2009 Science X (SET 2)

If the X gamete of the male fuses with the X gamete of the female, then the offspring will be female. On the other hand, if the Y gamete of the male fuses with the X gamete of the female, then the offspring will be male.

26. What is ‘hydrotropism’? Describe an experiment to demonstrate ‘hydrotropism’’? Answer: The growth movement of a plant part in response to water is called ‘hydrotropism’. Experiment to demonstrate hydrotropism: Take two small beakers and label them as A and B. Fill beaker A with water. Now, make a cylindrical-shaped roll from a filter paper and keep it as a bridge between beakers A and B, as shown in the figure. Attach few germinating seeds in the middle of the filter-paper-bridge. After this, cover the entire set-up with a transparent plastic container so that the moisture is retained.

CBSE 2009 Science X (SET 2) It will be observed that the roots of the germinating seeds will grow towards beaker A.

This experiment demonstrates the phenomenon of hydrotropism.

27. (a)

Draw a sectional view of the human heart and label on it Aorta, Pulmonary arteries, Vena cava, Left ventricle.

(b)

Why is double circulation of blood necessary in human beings? OR

(a)

Draw the structure of a nephron and label the following on it: Glomerulus, Bowman’s capsule, Renal artery, Collecting duct.

(b)

What happens to glucose that enters the nephron along with filtrate?

Answer (a)

CBSE 2009 Science X (SET 2) (b)

The movement of blood twice through the heart is known as double circulation. Double circulation is necessary in human beings as it allows separation of oxygenated and de-oxygenated blood for a more efficient supply of oxygen to the body cells. This efficient system of oxygen supply is very useful in warm-blooded animals such as human beings. As we know, warm-blooded animals have to maintain a constant body temperature (by cooling themselves when they are in a hotter environment and by warming their bodies when they are in a cooler environment). Hence, they require more O2 for more respiration, so that they can produce more energy to maintain their body temperature. Thus, the circulatory system of humans is more efficient because of the double circulatory heart. OR

(a)

(b)

The glucose that enters the nephron along with the filtrate is selectively reabsorbed as the urine flows along the tube.