SUMMATIVE ASSESSMENT –II

SCIENCE (Theory)

Class – X

(Solutions)

SECTION-A

1.         When a chemical reaction occurs, new products are obtained.

2.         Nephron.

3.  P = V2	⇒   P µ 1	⇒   R µ 1
R	R	P

Therefore 60 W bulb has a higher resistance.

4.         It is property due to which a crystalline substance loses water of crystallization when exposed to air and becomes amorphous, e.g.,

Na2CO3.10H2O ¾¾^air® Na2CO3.H2O + H2O

5.

	Tropic movements	Nastic movements
(i)	Direction of movement is in the direction	(i) Direction of movement is not determined
	of the stimulus.	by the direction of stimulus.
(ii)	Movements are slow.	(ii) Movements are fast.
	Example:	Example:
	The growth of the pollen tube towards a	The folding up and drooping of leaves of
	chemical produced by an ovule during the	the sensitive ‘touch-me-not’ plant.
	process of fertilization in a flower.

6.         Lines indicating the presence of magnetic field in a region are called magnetic lines of force.

7.         Displacement reaction is a reaction in which more reactive element displaces less reactive elements from its salts.

Example:            2KI (aq ) + Cl₂ (g ) ¾¾® 2KCl (aq ) + I₂ (g )

It is a displacement reaction.

8.         Chemical formula is a formula of a compound formed with the help of symbols and valency of elements and radicals.

Information conveyed by a chemical formula:

(i)        It conveys the name of the compound.

(ii)      It conveys the number and kind of atoms present in one molecule of compound.

(iii)    It conveys the valency of atoms present in it.

(iv)    It represents the molecular weight of the compound.

(v)     It indicates that the compound is not electrically charged. It is neutral molecule. For example, formula CaCO3 conveys following information:

(i)        It stands for calcium carbonate.

(ii)      It represents the one mole of calcium carbonate. Two molecules of calcium carbonate would be written as 2CaCO3 and so on.

(iii)    It tells that each formula of CaCO3 contains 1 atom of Ca, 1 atom of C and 3 atoms of O.

(iv)    It stands for 100 parts by weight of CaCO3. (40 + 12 + 3 x 16 = 40 + 12 + 48 = 100)

(v)      The ratio among Ca : C : O is 40 : 12 : 48 by weight.

9.         (i) CO2 is formed.

Na2CO3 + H2SO4 (dil.) ¾¾® Na2SO4 + CO2 + H2O (ii) SO2 is formed.

S + 2H2SO4 (conc.) ¾¾® 3SO2 + 2H2O

(iii)   SO2 + Ca(OH)2 ¾¾® CaSO3 + H2O Lime water turns milky.

10.     (i) Mineral: It is naturally occurring substance from which a metal may or may not be extracted profitably, e.g., Borax is mineral from which boron cannot be extracted economically.

(ii)      Ores: They are naturally occurring rocky substances which contain sufficient quantity of minerals from which metals can be extracted profitably, e.g., Al is extracted from Bauxite.

(iii)   Gangue: They are rocky materials present in the ores along with the minerals, e.g., SiO2 is present as gangue in ore of iron.

11.    (i) It is because metals can loss electrons easily to form positive ions, therefore regarded as electropositive elements.

(ii)      It is because copper is less reactive than Zn, therefore, it cannot displace Zn from ZnSO4

solution.

Cu + ZnSO4 ¾¾® No reaction

But when Zn is dipped in copper sulphate solution, it displaces copper from CuSO4 to form ZnSO4 which is colourless. Reddish brown copper metal gets precipitated because Zn is more reactive than Cu.

Zn + CuSO4 ¾¾® ZnSO4 + Cu

Zinc  (Blue)           (colourless) Copper

(iii)            It is because oxide layer is formed on the surface of aluminum due to which it does not react further because it is non-penetrating layer.

12.

13.     (a) Glottis is guarded by epiglottis to prevent food from entering the windpipe at the time of swallowing.

(b)  The lung alveoli are covered with blood capillaries for the easy diffusion of respiratory gases, since both alveoli and blood capillaries are thin-walled.

(c)  The wall of trachea is supported by cartilage rings so that it does not collapse when there is not much air in it.

14.     Male gonads are testes and female gonads are ovaries in human beings. Functions of Testes:

(i)        Testes produce sperms, the male haploid gametes.

(ii) They produce male sex hormones, i.e., testosterone. Functions of Ovaries:

(i)        They produce ova, the female haploid gametes.

(ii)      They produce female sex hormones i.e., estrogen and progesterone.

15.     (a)

(b)  Req = R1 + R2 + R3 = 5 + 10 + 15 = 30 W

V = V1 + V2 + V3 + V4 + V5 = 2 + 2 + 2 + 2 + 2 = 10 V

\ I = ^V = ¹⁰ = ¹ A R _eq 30 3

16.     The strength of the magnetic field produced at the centre of a circular coil of radius r, having N turns and carrying a current I, is given by:

_{B =} ^mo ^NI _tesla

2r

Thus the strength of the magnetic field in the coil is:

	µ	1
(i)  inversely proportional to the radius of the loop.  B
		r

(ii)        directly proportional to the number of turns. (B µ N)

(iii)      directly proportional to the current passing through it. (B µ I)

17.     (a) Methane, Carbon di-oxide, Hydrogen and Hydrogen sulphide

(b) Advantages of biogas over fossil fuels:

(i)        Biogas burns without smoke and does not cause air pollution while fossil fuel burns and causes air pollution.

(ii)      Biogas does not leave any residue after burning while fossil fuel leaves residue like ash which have a disposal problem.

(iii)   Biogas is cheaper than fossil fuel.

18.     (a) Solar panals

(b) Solar energy.

(c) Because Rajasthan gets a lot of sunshine throughout the year.

(d) Solar cell.

(e) General awareness, concern for the environment to improve it, desire to help people.

19.     The containers made up of copper or aluminium is suitable for storing the given solutions, can be decided by studying their reactions:

(i)    Reaction of copper with

(a)   Dil. HCl. Cu + dil. HCl ¾¾® No reaction. So it can be stored in Cu container.

(b)  Dil. HNO3. Being a strong oxidizing agent, dil. HNO3 reacts with copper, so it cannot be stored in copper container.

(c)   ZnCl2. Copper is less reactive than zinc so it does not react with ZnCl2 solution. Therefore it can be stored in copper container.

(d)  H2O. Copper does not react with water. So its container can store H2O in it.

(ii)  Reaction of Aluminium with

(a)  Dil. HCl. Al reacts with Dil. HCl, so it can not be kept in aluminium container. 2Al + 6HCl ¾¾® 2AlCl3 + 3H2

(b)  Dil. HNO3. When dil. HNO3 is kept in Al container, it forms a protective layer of aluminium oxide on it, therefore it can be kept in Al container.

(c)   ZnCl2. Al is more reactive than zinc, so it cannot keep ZnCl2 solution in it. 2Al + 3ZnCl2 ¾¾® 2AlCl3 + 3Zn

(d)  H2O. Al does not react with water (hot or cold). Therefore water can be kept in Al container.

Aluminium is attracted by steam to form aluminium oxide and hydrogen.

2Al (s ) + 3H₂ O (g ) ¾¾® Al₂ O₃ (g ) + 3H₂ (g )

Or

The reactions of zinc granules with various reagents are as follows:

(i)          Dil. H2SO4

Zn (s ) + H₂SO₄ (aq ) ¾¾® ZnSO₄ (aq ) + H₂ (g )

Zinc sulphate

(ii)  Dil. HCl

Zn (s ) + 2HCl (aq ) ¾¾® ZnCl₂ (aq ) + H₂ (g )

Zinc sulphate

(iii)      Dil. HNO3

Dil. HNO3 is an oxidizing acid so its reaction with a metal (e.g. Zn) is different than other dilute acids.

4Zn (s ) + 10 HNO₃ (aq ) ¾¾® 4ZN (NO₃ )₂ (aq ) + 5H₂ O (l ) + N₂O (g )

Zinc Nitrate                                Nitrous oxide

(iv)      NaCl solution

Reaction does not take splace.

Zn (s ) + NaCl (aq) ¾¾®  No reaction

(v)  NaOH solution

Zn (s ) + 2NaOH (aq ) ¾¾® Na₂ ZnO₂ (aq ) + H₂ (g )

Sodium zincate

Thus, hydrogen gas is evolved with H2SO4, HCl and NaOH, nitrous oxide gas is evolved with dilute HNO3 and no reaction takes place with NaCl solution.

20. (a) ‘Activity series’ of metals is the series in which metals are arranged in decreasing order of their reactivities.

Mg > Al > Zn > Fe > Cu is in a decreasing order of reactivity.

(b) (i) When zinc is placed in copper sulphate solution, the solution becomes colourless and brown colour copper metal is depicted.

Zn (s ) + CuSO₄ (aq ) ¾¾® ZnSO₄ (aq ) + Cu (s)

(ii)    Copper does not react with ferrous sulphate because it is less reactive than iron. No change takes place.

(f)    Sodium metal combines with hydrogen to form Sodium hydride. 2Na + H2 ¾¾® 2NaH (Sodium hydride)

Or

(i)        Froth Floatation process: It is the process to concentrate sulphide ore. The ore is mixed with water and pine oil and mixture is agitated with the blast of air. Froth is formed. Sulphide ore gets collected in froth whereas impurities are left behind e.g., Zinc Blende (ZnS) is concentrated by Froth Floatation process.

(ii)      Roasting of an ore: The process of heating sulphide ore in presence of oxygen so as to

convert it into oxide is called roasting, e.g., 2ZnS + 3O2 ¾¾® 2ZnO + 2SO2

(iii)    Calcination of an ore: It is defined as heating of ore in absence of oxygen so as to convert it

into oxide, e.g.,

ZnCO₃   ¾¾®^heat   ZnO + CO₂

21.

                                                        oesophagus

                                                        pancrease

                                                      

(c)   The function of the enzyme ‘pepsin’ in the digestion process is that it breaks down proteins into peptones in acidic medium of gastric juice.

Or

(i)

                                                         kidney

                                                          ureter

                                                         urinary bladder

                                                         urethra

(ii)        The two major components of normal human urine are water and nitrogenous substances, most of which is urea.

22.      (i)   According to Joule’s law of heating, the heat H

produced in a wire of resistance R while

carrying a current I in time 't ' is directly proportional to the square of current, resistance and time.

H = I² Rt

Proof: Work done to carry a charge dq against a potential difference V is, d W = Vdq = VIdt ⇒ W = VIt = I² Rt

This work done is dissipated as heat energy.

(ii)    Commercial unit is kWh.

1 kWh = 3.6 ´10⁶  joules

(iii)   Resistance of 40 W bulb = ²²⁰²

	40
Net resistance = 4 x	2202
	= 4840 W
	40

Current drawn and flowing through them = I = ²²⁰ = ²²⁰  = 0.045 A

R      4840

If one bulb fuses, no current flow will be seen in them.

Or

(a) Since resistivity depends neither on the length nor on the cross-sectional area of the conductor, the resistivity will remain unaffected in all variations. Also here material is same.

(b)

23.     Electrical energy used by:

(a)  4 bulbs of 60 W = 4 x 60 x 6 x 30 = 43200 Wh

(b)  3 tubelights of 40 W = 3 x 40 x 8 x 30 = 28800 Wh

(c)   300 W refrigerator = 300 x 24 x 30 = 216000 Wh

(d)  750 W mixer = 750 x 1 x 30 = 22500 Wh

(e)  TV of 100 W = 100 x 6 x 30 = 18000 Wh

Net energy consumption = 328500 Wh = 328.5 kWh = 328.5 units Cost for first 50 units = 2.50 x 50 = Rs.125.00

Cost for the remaining units = 3.00 x 278.50 = Rs.835.50 Total cost of electricity consumed = Rs.960.50

Or

(i)        Series

Net resistance = R60 + RH

Where R60 is the resistance of 60 W bulb and RH is the resistance of the heater.

		V2
Heat produced with a source of potential V (H) =			t
	R 60	+ R H

R100 – Resistance of 100 W bulb is less than that of R60.

\ Heat produced in same time 't ' should be more with 100 W bulb than with 60 W bulb.

(ii)      Parallel

Net resistance in parallel will be, R =	R	60 R H

R ₆₀ + R _H

This will be less than R60 and RH.

Heat produced, H = ^V2  t

R

If 60 W is replaced by 100 W bulb, the resistance R will further reduce. So heat produced will be increased.

24. (a) Magnetic field: Surrounding a magnet its influence is felt by any other magnetic element. It may be an attractive of a repulsive influence.

(b)  The direction of magnetic field at a point is determined by drawing a tangent at that point. The direction of tangent gives the direction of magnetic field.

(c)   Aim: To demonstrate the direction of the magnetic field generated around a current carrying conductor.

Procedure:

(i)        Obtain the concentric circles pattern of iron fillings around the copper wire by flowing current through it as shown.

(ii)      Place a magnetic needle (compass) at any point (P) over a circle.

(iii)    Observe the direction of needle.

(iv)    Show the direction by arrows.

Conclusion: The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at that point. The direction of the field is perpendicular to the plane of the coil and directed inwards for the clockwise current flowing. For anticlockwise current, it will be outwards.

Or

Pure iron is not used for making permanent magnets because it cannot retain their magnetism for long time and used only for electromagnet since alloys of iron and steel have strongly magnetized and have a capacity to hold it for a longer time period, they are used for permanent magnets.

Material used for permanent magnets – ALNICO

Formation of a permanent magnet electrically: Permanent magnets can be formed by placing a hard steel rod in the strong uniform magnetic field produced by the solenoid. Steels have the quality to retain its magnetism after switch off the solenoid current.

Permanent magnets are used in:

(i) Galvanometer          (ii) Ammeter

25.     The solution remains colourless because HCl is acid and It does not react with phenolphthalein.

26.     (a) Transpiration.

(b) Water loss due to evaporation from the plane is called transpiration.

27.     No change will be there i.e. the resistivity 'r ' will be same because it is a material constant.

28.     (b)

29.     (b)

30.     (a)

31.     (b)

32.     (b)

33.     (c)

34.     (a)

35.     (c)

36.     (b)