Second Summative Examination -2022(Physical Science ,class -X )

 Group - A 

1. Chose the correct answers :  1x7 = 7 

a) What will be the volume of 3.2 g of oxygen at S.T.P .

i) 22.4 L  ii) 2.24 L   iii) 0.224 L  iv) 0.0224 L 

b) The co-efficient of linear expansion of solid depends only on the unit of 

i) Length ii) Area   iii) Temperature iv) None of those 

c) Unit of resistance is 

i) Ampere  ii)  Ohm   iii) Coulomb  iv) Joule 

d) Which one is not conductor of electricity 

i) Copper ii) Gold  iii) Aluminium  iv) Plastic 

e) Which of the following compounds does not conduct electricity ?

i) Starch ii) Vinegar   iii) Table salt iv ) Baking soda 

f) Which of the following is used to dry moist ammonia ? 

i) Conc. H₂SO₄     ii)     P₂O₅  iii) CaO   iv) CaCl₂ 

g) Which of the followings is an ore of Aluminium ? 

i) Bauxite  ii) Haematite iii) Malachite  iv) Chalcopyrite 

Ans  : a) ii) 2.24 L  b) iii) Temperature c) ii) Ohm  d) iv) Plastic e) i) Starch f) iii) CaO g) i) Bauxite 

Group -B 

2.Very short answer type questions: 1x9 =9 

a) CaO and CO₂ are produced on heating of CaCO₃ .( T or F)

b) S.I unit of thermal conductivity is _------------.

c) Write down the relation between ∝ ,β ,४ for a solid .

d) S.I unit of charge is _--------------.

e) Resistance of a conductor indirectly proportional to the length of the conductor.(True or False)

f) The electrode connected to positive terminal of battery is called cathode .(True or False)

g) Pure water _--------- conductor of electricity.

OR 

Which ion migrates towards the cathode during the electrolysis of aqueous solution of CuSO₄ using copper electrodes ?

h) Write down the formula of black precipitate when H₂S gas is passed through an aqueous solution of lead nitrate . 

i) Write down the balanced chemical reaction for extraction of Fe from Fe₂O₃ by Thermite process.

Answer:

a) T b) Watt.m⁻¹K⁻¹  c) α =β/2 = ४/3 d)Coulomb  e);False  f) False   g) very poor  Or Cu⁺²  h) PbS.  i) Fe₂O₃ + 2Al = Al₂O₃ + 2Fe + heat 

Group -C 

3. Short Answer type Questions. 

a) How does the resistance of a semiconductor change with increase of temperature.What is the unit of specific resistance or resistivity ?

b) Write the reaction of ammonia preparation by Haber's process mentioning the condition of reaction.

c) Arrange in order of increasing carbon content in wrought iron, cast iron and steel .

Ans : 

a) Resistance of semiconductor decreases with increase of temperature . Unit of specific resistance is Ohm.m .

b) N₂ + 3H₂ → 2NH₃

Condition of reaction - At 200 Atmospheric pressure and 400-450 ⁰C with iron catalyst nitrogen and hydrogen react to produce ammonia.

c) Order of carbon content of different iron : wrought iron<Steel <cast iron 

Group-D 

4.Long answer type questions:

a) On strong heating of limestone (CaCO₃) decomposes into quicklime and CO₂ . How much quantity of quicklime will be produced on complete decomposition of 30 g of limestone by the above reaction ? 

b) What is the Thermal conductivity ? What is its units in SI system ? Write the expression for the thermal conductivity explaining the meaning of each term .

c) State Ohm's law .If the potential difference between two ends of a conductor be 15 volt for which current flowing through is 3 ampere .Find the resistance of the conductor.

d) Write the expression for the equivalent resistance for series combination of two resistances r₁ and r₂ .If the resistance of two coils of wire are 3 Ω &6 Ω.What will be the equivalent resistance ?

Or 

Write the Joule's law of heating effect of current with mathematical expression. 

e) Write down the cathode and anode reaction for the electrolysis of acidified water using platinum electrode.Which materials are used on anode and cathode during electro refining of impure copper .

f) Write down the balanced chemical reactions for the industrial manufacture of SO₃ from SO₂ by contact process .How is H₂SO₄ prepared from SO₃ produced ?

  Ans: 

a) CaCO₃  = CaO + CO₂ 

Molecular weight of  calcium carbonate (CaCO₃ ) [ Ca = 40 ,C = 12 , O = 16]

= 40 + 12 + 16 x 3 = 40 + 12 + 48 = 100 and molecular weight of  CaO = 40 + 16 = 56 .

From the above reaction we get 56 g of quicklime( CaO )from 100 g of limestone( CaCO₃) 

So from 30 g . of limestone we get 56/100 x 30 = 16.8 g of quicklime .

b) Thermal conductivity is the rate of flow of heat energy per unit area at unit temperature gradient .

Its SI unit is Watt. m⁻¹ K⁻¹ .

Expression of thermal conductivity ; 

Q/t = - k A( T₁ - T₂) /L  = k A( T₂ - T₁ ) /L 

Here" k"  is thermal conductivity , T₂ > T₁  (T₂ ,  T₁ are temperature in hot and cold surface respectively ) 

Q/t = heat flow per unit time .A = area of surface through which heat is conducting .

c) Ohm's law :

Electrical Current flowing through a conductor is directly proportional to potential difference across the two ends of the conductor provided Temperature and other physical conditions remain constant .

If the potential difference between two ends is V and current flowing is I then according to Ohm's law , V ∝ I 

⇒V = R I (R = proportionality constant)

R is known as resistance of conductor.

This is mathematical expression of Ohm's law

 Here V = 15 Volt I = 3 amperes 

Hence from the above relation we get ,

15 = R X3 

∴ R = 15/3 = 5 Ohm .

Therefore resistance of the conductor is 15 Ω

d) 

Equivalent resistance for Series combination of two resistance r₁ 

and r₂ is R = r₁ + r₂ 

Here two resistances are 3 ohm and 6 ohm 

So equivalent resistance is R = 3 + 6 = 9 ohm.

Or 

Joule's law forheating effect of current .

1) If resistance(R) and time(t) remain constant then heat(H) generated due to current(I) is directly proportional to the square of current.

i.e H ∝ I² ( R, t = constant.)

2) Heat generated Is proportional to resistance when current and time remain constant.

i.e H ∝ R ( I, t = constant.)

3) Heat produced due flow of current is proportional to time of flow when resistance and current remain constant.

ie H ∝ t ( I,R = constant.)

Combining the above three equations we get ,

H ∝ I² Rt 

⇒ H = I²Rt (S I system)

e) Electrolysis of acidified water using platinum electrodes:

Water is ionised as 

H₂O → H⁺ + OH⁻

Cathode reaction:

2H⁺ +2e = 2H 

2H = H₂ 个

Anode reaction:

4OH⁻ -4e = 4H₂O + O₂个

So we get hydrogen gas from cathode and oxygen from anode .

For electro refining of impure copper a slab of impure copper is used as anode and a thin strip of pure copper is used as cathode.

f) 2SO₂+ O₂ → 2SO₃ 

(Conditions of reaction , temperature needed 400-450ªC, Catalyst V₂ O₅ ,pressure - 1- 2atm.

In order to produce sulphuric acid in contact process supher trioxide is absorbed in concentrated sulphuric acid to form oleum or fuming sulphuric acid . Next with oleum water is added to produce sulphuric acid .

H₂SO₄ + SO₃ →H₂S₂O₇(oleum)

H₂S₂O₇ + H₂O →2H₂SO₄