Set-3

CBSE 2009 Science X (SET 3) 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 3)

Section A 1. Why does 1 M HCl solution have a higher concentration of H+ ions than 1 M CH3COOH solution? 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.

2. 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

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. How is the induced current in a secondary coil related to current in a primary coil?

CBSE 2009 Science X (SET 3) Answer: A varying current in the primary coil induces a current in the secondary coil. The magnitude of the induced current depends on the ratio of the numbers of turns in the two coils. 5. State the rule which gives the direction of magnetic field associated with a current-carrying conductor. 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. 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. Write the name and chemical formula of the calcium compound used for disinfecting drinking water. How is this compound manufactured?

CBSE 2009 Science X (SET 3) Answer: The compound used for disinfecting drinking water is bleaching powder. The chemical formula of bleaching powder is CaOCl2. Bleaching powder is manufactured by the action of chlorine (Cl2) gas on dry slaked lime [Ca(OH)2]. The chemical equation involved in the process can be represented as:

Ca(OH)2 + Cl2

CaOCl2 + H2 O

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. Calculate the electric energy consumed by a 1200 W toaster in 20 minutes. Answer: The energy (E) consumed by an electric device of power P, in time t, is given as: E = Pt It is given that: P = 1200 W t = 20 min =

20 60

1 h 3

CBSE 2009 Science X (SET 3)

E = 1200 ×

1 3

400 W

0.4 kWh

Hence, the energy consumed by the given toaster is 0.4 kWh.

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 vinegar?

(b)

Describe with a chemical equation, what happens when sodium hydrogen carbonate reacts with ethanoic acid.

Answer (a)

Vinegar is 5-8% solution of ethanoic acid (acetic acid) in water.

(b)

When sodium hydrogen carbonate reacts with ethanoic acid, sodium acetate, carbon dioxide and water are obtained as products. The chemical equation for this process is: CH 3COOH + Ethanoic acid

NaHCO3

Sodium hydrogen carbonate

CH3COONa + CO 2 Sodium acetate

Carbon dioxide

+

H2O Water

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?

CBSE 2009 Science X (SET 3) (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)

How is the direction of electric current related to the direction of flow of electrons in a wire?

(b)

Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes.

Answer (a)

The direction of the electric current flowing through a wire is opposite to the direction of flow of electrons through the wire. The direction of flow of current in a circuit is taken by convention as the direction of flow of positive charges, i.e., from the positive terminal to the negative terminal of a battery, through the external circuit. Since the direction of flow of electrons (negative charges) in a circuit is opposite to the direction of flow of positive charges, the direction of flow of electric current is opposite to the direction of flow of electrons in a circuit/wire.

(b)

The current (I) flowing through a circuit is given by the amount of total charges (Q) passing in a unit time (t). It is given by: I

Q t

It is given that: Q = Total charge = 500 C t = 10 min = 600 s

CBSE 2009 Science X (SET 3)

I

500 600

0.83 A

Hence, 0.83 A current flows through the circuit.

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: (i)

Strength of forces between constituent elements

(ii)

Solubility of compounds in water

(iii)

Electrical conduction in substances

CBSE 2009 Science X (SET 3) (b)

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). 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,

CBSE 2009 Science X (SET 3) 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) Iron (III ) oxide

2Al(s) 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? 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.

CBSE 2009 Science X (SET 3) (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.

OR

(a)

Dispersion: The splitting of white light into its seven component colours is called dispersion.

CBSE 2009 Science X (SET 3) 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 3)

Section B 17. 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.

18. What is the mode of nutrition in human beings? Answer: Human beings have heterotrophic mode of nutrition.

19. Which compounds are responsible for the depletion of ozone layer? Answer Chlofluorocarbons (CFCs) are responsible for the depletion of the ozone layer.

20. 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.

21. Describe how hydro-energy can be converted into electrical energy. Write any two limitations of hydro-energy.

CBSE 2009 Science X (SET 3) 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.

22. List any four advantages of water harvesting. Answer The four advantages of water harvesting are as follows: (a) (b) (c) (d)

In this process, the evaporation is controlled. Instead, it percolates into the ground, thereby resulting in the re-charging of ground water. The stored water provides moisture to the vegetation in and around the area. Rainwater harvesting improves the quality of rainwater by the process of natural filtration of fluorides, nitrates, and salts. The stored water does not provide a breeding ground for mosquitoes and micro-organisms, unlike the stagnant water in ponds and lakes.

23. 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.

CBSE 2009 Science X (SET 3) 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. What are hormones? State one function of each of the following hormones. (i)

Thyroxin

(ii)

Insulin

Answer: Hormones are chemical messengers that regulate the physiological processes in a living organism. (i)

Thyroxin- It regulates carbohydrate, fat, and protein metabolism in the body.

(ii)

Insulin- It is secreted by the pancreas and regulates the blood sugar level in the body.

26. What is ‘Phototropism’? How does it occur in plants? Describe an activity to demonstrate phototropism. Answer: The growth movement of plants in response to light stimulus is known as phototropism. In plants, the bending of shoots towards light is known as positive phototropism, while the bending of roots away from light is known as negative phototropism. Activity: Take two seedlings of mustard plant and keep them in a small bottle containing water. Close the bottle with a split cork and keep it inside a wooden box

CBSE 2009 Science X (SET 3) (provided with a small opening on one side). After this, keep the box near a light source in such a way that the opening in the box faces the light source.

Response of a plant to light After 2-3 days, it will be observed that the shoots bend towards light, while the roots bend away from light. This type of growth movement in response to light stimulus is known as phototropism. 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 3) (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.