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Wednesday, July 23, 2014

8th/9th Chapter-Sound Physics CBSE Solved paper

IX Class Question solution for Physics Chapter Sound
1. How sound is produced?
Answer:   Sound is produced by the vibration of vibrating object.
2. What do you understand by a ‘wave’?
Answer:  A periodic disturbance created in material medium that transfer sound and light energy is called wave.
3. Write three differences between sound and light waves.
Answer:   sound wave is Mechanical wave that require material medium for propagation where as light waves are electromagnetic wave that can travel in vacuum.
4. What do you understand by “sound energy cannot be produced”?
Answer: Sound energy cannot be produced on its own. Some mechanical energy is required to make an object vibrate. It is the mechanical energy of the vibrating object which travels through a medium and ultimately reaches the ear.
 5. What is the name of the wave that can travel through vacuum?
Answer:   Electromagnetic wave
6. Explain by some experiment that sound waves require medium for their propagation.
Answer: An electric bell is suspended inside an airtight glass bell jar connected to a vacuum pump. As the electric bell circuit is completed, the sound is heard. Now if the air is slowly removed from the bell jar by using a vacuum pump, the intensity of sound goes on decreasing and finally no sound is heard when all the air is drawn out. We would be seeing the hammer striking the gong repeatedly. This clearly proves that sound requires a material for its propagation.
 7. How sound waves travel through some medium?
Answer:   Sound waves work travel through some medium by passing vibrations from molecule to molecule. If there is no medium, then there no molecules to pass vibrations.
8. Why sound waves do not propagate through vacuum?
Answer:   If there is no medium, then there no molecules to pass vibrations.
9. What are the transverse waves? Give two examples.
Answer:   Transverse waves:
A wave in which the particles of the medium vibrate at right angles to the direction, in which the wave is moving, is called transverse wave. Example: Light waves.
10. What are longitudinal waves? Give two examples.
Answer:   Longitudinal waves:
A wave in which the particles of the medium vibrate back and forth in the same direction in which the wave is moving is called longitudinal wave. Example: sound waves.
11. Give two points of difference between longitudinal and transverse waves.
Answer:   Differences between the transverse wave and longitudinal wave:-
Transverse wave :-
(1)A transverse wave is a wave in which variation of the amplitude of a wave is perpendicular to the direction of propagation of wave.
(2) Light wave, wave in string, wave developed in water etc.
(3)In light wave electric and magnetic field oscillates normally to the direction of motion of the wave.
(4) It may propagate in the vacuum.
Longitudinal wave :-
(1)A longitudinal wave is a wave in which variation of the amplitude of wave is in the direction of the propagation of wave.
(2)sound wave, oscillation in the spring.
(3) In spring wave elongation or compression occurs along the direction of motion of the wave.
(4) It can not propagate in the vacuum.
12. How will you prove that the sound waves exhibit longitudinal behaviour?
Answer:   Take a tuning fork and a hard pad. Allow the tuning fork to strike the pad which makes the prongs to vibrate. When it starts vibrating, the inward and outward movements takes place in prong which causes the movement of inward and outward towards the mean position.The tuning fork is given as,

The vibaration of the tuning fork produces the compressions and refractions of the sound in the air,

When the tuning fork vibrates in air, they force the particles of the air to vibrate back and forth by a small distance. While vibrating, when the prong moves to the right side, it sends out a compression and when the prong moves to the left, it produces a rarefraction in air.
The longitudinal waves in series produce compressions and rarefractions in air from the tuning fork. These compressions and rarefractions of sound waves is formed by the vibrating particles causing vibration in the ears, the eardrum vibrates for reproduction of sound.
13. What are rarefaction and compression in case of sound waves?
Answer:   Compressions: Areas in the wave where the air molecules are pushed close together and so at a slightly higher pressure.
Rarefaction: Areas in the wave where the air molecules are further apart and so at a slightly lower pressure.
14. Distinguish between crests and troughs.
Answer:   The highest point of a wave is known as its crest while the trough is the lowest point of the wave. Wavelength is the horizontal distance between successive crests or troughs.
15. Write the SI unit of velocity of a wave.
Answer:   m/s
16. What are the factors that describe the sound wave and define them?
17 .Why is a thundering sound heard later than lightening?
Answer:   This because the speed of sond is much lesser than that of light.
18. Sound travels with different speeds in different media. Comment.
Answer:   Sound waves need to travel through a medium such as a solid, liquid, or gas. The sound waves move through each of these mediums by vibrating the molecules in the matter. The molecules in solids are packed very tightly. Liquids are not packed as tightly as solids. And gases are very loosely packed. The spacing of the molecules enables sound to travel much faster through a solid than a gas. Sound travels about four times faster and farther in water than it does in air. This is why whales can communicate over huge distances in the oceans. Sound waves travel about thirteen times faster in wood than air. They also travel faster on hotter days as the molecules bump into each other more often than when it is cold.
19. How far are a compression and its nearest rarefaction in a longitudinal wave?
Answer:   Wavelenth/2
20. Define sound ranging.
Answer:   The method of  the determination of the location of a source of sound waves by measuring the time lapse between their transmission and their reception
21. What is the frequency range of sound for human beings?
Answer:   20Hz to 20000Hz
22. What are the ultrasonic and supersonic waves?
Answer:   Ultrasonic waves refers to sound of  frequencies greater than those that can be heard (usually frequencies above 20 kHz).
Supersonic refers to sound of velocities faster than the speed of sound (in the medium under consideration).
23. What type of waves are produced by animals like bats and dolphins?
Answer: Ultrasound above 20000Hz
24. Explain two applications of ultra sound waves?
Answer:   Ultrasound is a wave with frequency greater than the upper limit of human hearing. These waves travel along well -defined paths and can even penetrate obstacles.
Some important applications of ultrasound are:
a. It is used for medical diagnosis and therapy and also to clean parts located in hard-to-reach places, for example, spiral tube, electronic components etc.
b. Ultrasound is used to detect cracks and flaws in metal blocks. Such as aeroplane wings can be checked for cracks that would be invisible on the surface.
c. Its use in scanning goes far beyond pregnancies. Many other parts of the body are analysed using it (bladder gallstones, the heart, etc.)
d. Detection of developmental/ structural abnormalities in the fetus. Evaluation of the heart and diagnosis of cardiac problems. This technique is called ‘Echocardiography’.
25. Ultrasound is also used to break small ‘stones’ formed in the kidneys into fine grains.25. Explain how ultrasound waves are used to detect a flaw in an object?
Answer:   The ultrasound waves are allowed to pass through metal block to which are fitted detectors to detect the waves. Ultrasounds can be used to detect minor cracks or flaws in metal block. For this, ultrasonic waves are allowed to pass through metal blocks and detectors are used to detect the transmitted waves. If there is a crack in metal block, these waves get reflected back, thus indicating the presence of defects or flaws like cracks in the metal block. 26. Which sound wave is used in ECG (echocardiography)?
Answer:   ultra sound wave
27. Give the full form of SONAR.
Answer:   SONAR: Sound Navigation And Ranging
28. Name the technique used to measure the depth of a sea.
Answer:   Sound ranging
29. How will you determine the depth of a sea using SONAR?
Answer:   ONAR is an acronym for Sound Navigation And Ranging. It is an acoustic device used to measure the depth, direction, and speed of under-water objects such as submarines and ship wrecks with the help of ultrasounds. It is also used to measure the depth of seas and oceans.

A beam of ultrasonic sound is produced and transmitted by the transducer (it is a device that produces ultrasonic sound) of the SONAR, which travels through sea water. The echo produced by the reflection of this ultrasonic sound is detected and recorded by the detector, which is converted into electrical signals. The distance ( d ) of the under-water object is calculated from the time ( t ) taken by the echo to return with speed ( v ) is given by 2d = v × t . This method of measuring distance is also known as ‘ echo-ranging’.
30. How do the bats fly in dark?
Answer:   Bats fly in the darkness of night without colliding with other objects by this method called echolocation. Bats emit high-frequency ultrasonic squeaks while flying & listen to the echoes produced by the reflection of their squeaks from the objects ( or obstacles ) in their path. From the time taken by the echo to be heard, bats can judge the distance of the object (or obstacle) in their path and  hence avoid it by changing the direction.
Notes: Bats search their prey at night by this method only.This happens as follows : Bats emit high-frequency ultrasonic squeaks while flying & listen to the echoes produced by the reflection of their squeaks from the prey like a flying insect.From the time taken by the echo to be heard, bats can judge the distance of the insect & hence can catch it.
31. How RADAR is different from SONAR?
Answer:   SONAR (Sound Navigation and Ranging) uses sound wave which is mechanical energy  to "look" through water or other media, and RADAR (Radio Direction and Ranging) uses electromagnetic radiation(radio waves) to "look" through the air or other media.
RADAR signals are mostly used for ground or atmospheric observations whereas SONAR signals are ideal for navigation and measurement under water.
32. Explain the function of ear by explaining its each part?
Answer:   The outer ear is called ‘pinna’ collects the sound from the surroundings. The collected sound passes through the auditory canal . At the end of the auditory canal there is a thin membrane called the ear drum or tympanic membrane. When a compression of the medium reaches the eardrum the pressure on the outside of the membrane increases and forces the eardrum inward. Similarly, the eardrum moves outward when a rarefaction reaches it. In this way the eardrum vibrates. The vibrations are amplified several times by three bones (the hammer, anvil and stirrup) in the middle ear. The middle ear transmits the amplified pressure variations received from the sound wave to the inner ear. In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.
Note: The stirrup bone of the middle ear is the smallest bone in human body.
33. Distinguish between loudness and intensity of sound.
Answer:    Intensity depends on the energy per unit area of the wave and it is independent of the response of the ear, but the loudness depends on energy as well as on the response of the ear.
34. Why are ceilings of concert halls curved?
Answer:    The ceilings of concert hall are curved, so that sound after reflection from it reaches all the corners of the hall, and hence, is audible to everyone in the hall.
35. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer:    Number of vibrations produced in 1 second = 100
Number of vibrations produced in 1 minute (60 s) = 100 × 60 = 6000.
36. Give two practical applications of the reflection of sound waves. [2010]
Answer:    (i) In stethoscope the sound of patient’s heartbeat reaches the doctor’s ears by multiple reflections in the tubes.
(ii) Megaphones are designed to send sound waves in particular direction are based on the  reflection of sound.
37. Why are longitudinal waves called pressure waves?
Answer:   Sound waves travels in the form of compression and rarefactions, which involve change in pressure, and volume of the air. Thus they are called pressure waves.
38. What are harmonics?
Answer:    harmonics are notes of frequency which integral multiple of the fundamental frequency produced by a device. For e.g. third harmonic is 3 times the fundamental frequency.
39.   What are fundamental note and overtones?
Answer:    When a sound is produced, there are tones of different frequencies. The tone of lowest frequency is called fundamental note and the tones of higher frequency are called overtones.
Q.40   Sound travels faster on a rainy day than on a dry day. Why?
Answer:    Sound travels faster on rainy day because the velocity of sound increases with increase in humidity. On rainy day humidity is more thus velocity of sound is aso more.
Q.41   Why are the window panes of houses sometimes cracked when a bomb explodes even at large distance?
Answer:    The windows breaks because of the generation of shock waves in the explosion.
Q42   If the tension in the wire is increased four times how will the velocity of wave in a string varies?

Answer:    velocity of the wave in string is directly proportional to the square root of the tension thus if tension is increased 4 times the velocity will be doubled.

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Saturday, July 5, 2014

Edugain HOTS Questions with Answer CBSE Chapter Magnetic Effects of Electric Currents

HOTS Questions with Answer:  Magnetic Effects of Electric Currents

Q1.On what factors does the magnetic field intensity at the centre of the circular coil carrying current  depend ?
Answer: The magnetic field intensity at the centre of the circular coil is directly proportional to current and inversely proportional to radius of the coil. So, in both the cases ,that is, twice the current as well as half in radius, the magnetic field intensity gets doubled.

The magnitude of the magnetic field (B) at the of the coil is:
(i). directly proportional to the current (I) flowing it.
      i.e.   B α I                           ①
(ii). Inversely proportional to the radius (r) of the coil
    i.e.  B α 1/r                              ②
From ①, and , we get

             B α I/r

Q2.State the principle used to determine the force experienced by a conductor carrying current in uniform magnetic field ?

Answer: .Fleming’s Left Hand Rule-Stretch the first three fingers of the left hand mutually perpendicular to each other such that the fore finger points in the direction of magnetic field, the middle finger points in the direction of current, then the thumb will indicate the direction of force experienced by the conductor.
Q3.On what factors does the force experienced by a conductor carrying current in uniform magnetic field depend?
Answer: .Force experienced by a conductor depends on
(a)Current and
(b)The perpendicular distance between that point and the conductor.
(c)Magnetic field strength

Q4.On what factors does the strength of a magnetic field at a point due to a straight conductor carrying current depend ?
Answer:.(a)Magnitude of electric current and
(b)perpendicular distance between that point and the . Conductor.
The magnitude of the magnetic field (B) at the of the coil is:
(i). directly proportional to the current (I) flowing it.
      i.e.   B α I                           ①
(ii). Inversely proportional to the radius (r) of the coil
    i.e.  B α 1/r                              ②
(iii). directly proportional to total number of turns (N) in the coil.
           i.e. B α N                              ③
From ①, ② and ③, we get

             B α I x N/r

Q5.Differentiate between direct current and alternating current.
Direct current
In direct current
 (a)It has constant
a) It varies in magnitude.
(b)It has constant
b) It changes its direction alternatively
(c)It is less dangerous in terms of terms of shock.
c) It is more dangerous in eclectic shock.

Q6.A switch is always connected in
(a)earth wire         (b)neutral wire                   (c)live wire

Answer: . It is always connected with live wire.

Q7.What type of connection is used in household circuits?
Answer: .In household circuits all electrical appliances are connected in parallel.

Q8.State the principle of the working of an electric motor.
Answer: .An electric motor works on the principle of force experienced by a current carrying conductor in a magnetic field. The two forces acting are equal and opposite. Since they act in different lines the bring rotational motion.

Q9.State the principle of a D.C generator.
Answer: .It is based on the principle of electromagnetic induction.

Q10.State the characteristics of magnetic field lines.
Magnetic field
 The space surrounding a magnet in which magnetic force is exerted is called a magnetic field.
The magnetic field has both magnitude as well as direction.

 The S.I.Unit of magnetic field is Newton/Ampere-meter. It is also called Tesla and is denoted by T.
1T=1Newton1ampere x1meter 
So, 1T=1 N/Am

The magnetic field (B)of earth near its surface = 0.3 x 10-4T.

(i)The direction of magnetic field is indicated by the arrow in the line at any point (tangent).
(ii)The field lines come out of the north pole and emerge into the south pole(closed loops are formed).
(iii)No two field lines will never ever intersect each other.

Q11.State Right Hand Thumb Rule.
Answer: .Hold the wire carrying current in your hand, such that the thumb points in the direction of current, the direction of the curled fingers will indicate the the direction of magnetic field.

Q12.Define the phenomenon overloading.
Answer: .If the total current drawn by all the appliances at a particular time exeeds the bearing capacity of that wire, the wires of the domestic wiring get heated.This Phenomenon is called overloading.

Q.13. How can it be shown that magnetic field exist around a wire carrying current?
Answer: By using magnetic compass which, shows deflection.
A current-carrying straight conductor is placed in the east-west direction. What

Q.14 Will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected on? (a) reversing the direction of flow of current (b) doubling the magnitude of current. The direction of earth’s magnetic field is from G-south to G-north.
Answer: Let current is from west to east. Therefore force is vertically upwards.
(a) By reversing the direction of current, the direction of will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled.

Q.15. A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane parallel to the wire. What will be the direction of the needle?
Answer: (i) along the tangent to a circle going anti-clockwise to an out coming current( to plane A).

Q.16.A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane perpendicular to the plane A, what will be the direction of the needle? Answer: .Any direction, as the needle is not influenced by a perpendicular field.

Q.17.If a magnetic needle is placed at the north pole in a horizontal plane, in what direction it will indicate? Why?
Answer: They will show random orientation as the magnetic field at the poles are along the vertical line and not on the horizontal plane.

Q.18.If a magnetic needle is placed at the north pole in a vertical plane, what will be its direction?
Answer: .They will stand vertically.

Q.19. Is a circular coil carrying current similar to magnet?
Answer: Yes

Q.20. What is the role of soft iron in the core of a solenoid?
Answer: It acts as an electromagnet.

Q.21. What are the factor on which the magnitude of the magnetic field (B) inside the solenoid depends on?

Answer: The magnitude of the magnetic field (B) inside the solenoid is:

(i). directly proportional to the to the current flowing through it.
            i.e.     B α I                           ①
(ii). directly proportional to the number of turns per unit length of the solenoid(n).
            i.e.      B  α n                         ②
       From ① and ②, we get
                B α nI
          Where n = N/l.
         Here, N = Total number of turns in the solenoid
          And   l = Length of solenoid.

Q. 22. What are the factor on which force acting on a current-carrying conductor placed in a magnetic field.

Answer: Magnitude of Force:- It has been found experimentally that the force (F) is:

(i). directly proportional to the current (I).

i.e. F∝ I ①

(ii). directly proportional to the length of the conductor inside the magnetic field.

i.e. F ∝ L ②

(iii). directly proportional to the magnitude of the magnetic field.

i.e. F α B ③

From ①, ② and ③, we get

F∝ ILB Or F=K x I x L xB

Q.23. What is magnetic flux?

Answer: The total number of lines of magnetic force in a material is called magnetic flux, f . The strength of the flux is determined by the number of magnetic domains that are aligned within a material. The total flux is simply the flux density applied over an area. Flux carries the unit of a weber, which is simply a tesla- meter2.

The number of magnetic lines of force cutting through a plane of a given area at a right angle is known as the magnetic flux density, B. The flux density or magnetic induction has the tesla as its unit. One tesla is equal to 1 Newton/(A/m). From these units, it can be seen that the flux density is a measure of the force applied to a particle by the magnetic field. The Gauss is the CGS unit for flux density and is commonly used by US industry. One gauss represents one line of flux passing through one square centimeter of air oriented 90 degrees to the flux flow.

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Magnetic effect of current class 10 Eduscore Questions with solution by cbse pathshala

Wednesday, June 25, 2014

Control and Coordination Study Material for class 10

10th Control and coordination
The organ system in an animal that serves to coordinate and control the functioning  of all other organ systems in the body is known as nervous system.

Nervous system works with the endocrine system to communicate, integrate and coordinate the functions of various organs and systems in our body and helps the body to respond to the external stimuli.

 In humans, the nervous system has two main divisions:
• The central nervous system (CNS)
• The peripheral nervous system (PNS)

The central nervous system consists of brain and spinal cord. It is regarded as the ‘thinker’ or ‘information processor’ in the body.

The peripheral nervous system includes the sensory and motor nerves and connects the central nervous system with the sense organs, muscles and glands of the body. The peripheral nervous system is regarded as ‘actor’ or ‘performer’ in the body.

Nerve cell or neuron

A neuron is the basic unit of nervous tissue. Our nervous system contains about 10 billion nerve cells, which communicate with each other in a specific manner.

Structure of the neuron

Each neuron has a central area called the cell body or cyton.

The cell body has a large central nucleus and cytoplasm. Several short, thread like branches called dendrites arise from the cell body. One branch arising out of the cell body is very long in comparison to others. This branch is called axon or nerve fibre.

Axon may or may not be covered by a fatty sheath called myelin sheath. This covering is missing at intervals. These gaps on the sheath are known as nodes of Ranvier.

Types of neurons
i. Sensory neurons, which transmit impulse from receptor (sense organ) to coordinator (brain or spinal cord).
ii. Motor neurons, which transmit impulse from modulator to effectors (muscle or glands).
iii. Connecting neurons, which connect sensory and motor neurons, found in the grey matter.


Nerves are thread like structures, which emerge from brain and spinal cord and branch out to almost all parts of the body. The nerves are composed of axons or nerve fibres bundled together like the strands of an electric cable 

Kinds of nerves

There are three kinds of nerves. These are:

i. Sensory nerves: These nerves contain sensory fibres. Sensory nerves bring impulse from sense organs to the brain or the spinal cord.
ii. Motor nerves: These nerves contain motor fibres. Motor nerves carry impulse from brain or spinal cord to the effector organ like muscle or glands.
iii. Mixed nerves: These nerves contain both sensory and motor nerve fibres and perform a mixed function.

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Saturday, June 21, 2014


Question:  How does baking powder differ from baking soda?
Answer:  Baking soda is a single compound which has sodium hydrogen carbonate which is  alkaline (basic) in nature
Baking powder is a mixture of sodium hydrogencarbonate and a mild edible(eatable) acid such as tartaric acid. When baking powder mixes with water, then the sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake to rise and hence 'soft and spongy'.The equation which takes place can be shown as:
NaHCO+ H+  ----> Na+ +  CO+ H2O
Question:  What will happen if heating is not controlled while preparing Plaster of Paris from gypsum?
Answer:  It may be noted that the temperature should be controlled carefully. It should not be allowed to rise above 152°C (425K) because, if whole of the water is lost then anhydrous calcium sulphate is produced, which is called dead burnt plaster and it does not have the properties of Plaster of Paris.

Question:   Explain how pH change in the river water can endanger the lives of aquatic animals.
Answer:  Living organisms can survive only in a narrow range of pH change. When pH of rain water is less than 5.6, it is called acid rain. When acid rain flows into the rivers, it lowers the pH of the river water. The survival of aquatic life in such rivers becomes difficult.

 Question:  What are the two main ways in which common salt (sodium chloride) occurs in nature? How is common salt obtained from sea water? Explain
Answer:  Salt exists in two forms in nature i.e. in sea water and in the form of Halite a mineral rock of common salt. Common salt can be prepared by evaporation of sea water. Sea water is collected in division of land and it is allowed to evaporate under sunlight. Water is evaporated leaving behind mixtures of salt, form which common salt is separated by dissolving it in suitable reagent and then, recrystallizing salt from the solution.
Question: Why aqueous solution of sodium carbonate is basic in nature?

Answer: Sodium bicarbonate is an amphoteric compound. Aqueous solutions are mildly alkaline due to the formation of carbonic acid and hydroxide ion:
NaHCO− 3 + H2O → H2CO3 + OH−  
Question: Why is an aqueous solution of ammonium chloride acidic in nature?
Answer: A basic component is the one that produces hydroxide (OH-) ions when dissolved in water. In aqueous solution of ammonium chloride, ammonium ions (NH4+) first associate with H2O and form ammonia and hydroxide ions.
NH4Cl + H2O = NH4+ + HCl ( equation 1)
NH4+ + H2O = NH3 + OH- (equation 3)
Since ammonium ions produce hydroxide ions, NH4+ are considered to be the basic components.
Question: Dry ammonia has no action on litmus paper but a solution of ammonia in water turns red litmus paper blue. Why is it so?

Answer: In dry state Ammonia contains no hydroxyl ions. On dissolving in water, it forms NH4OH which dissociates to give NH4 + and OH-ions. Thus solution becomes basic and turns red litmus paper blue.
NH3 (g) + H2O (l) ---------------> NH4OH (aq)
NH4OH (aq) --------------> NH4+ (aq) + OH- (aq)

Question:  What happens when (a) Solid sodium hydrogen carbonate is heated, (b) Chlorine gas is passed through dry slaked lime, (c) Gypsum is heated to a temperature of 373 K?
Answer: (a) When Solid sodium hydrogen carbonate is heated  from sodium chloride Na2CO3.10H2O (washing soda).
2NaHCO3 --------Heat---------->  Na2CO3 +H2O+CO2
(b) when Chlorine gas is passed through dry slaked lime, Bleaching powder is produced. Bleaching powderis represented as CaOCl2, though the actual composition is quite complex.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
(c) if Gypsum is heated to a temperature of 373 K it forms plaster of Paris, CaSO4 ½ H2O
CaSO4 2H2O --- -373 K ------>  CaSO4 ½ H2O + 3/2 H2O
Question: Give the Names of Raw Materials that are required for the manufacture of  washing soda by solvay process. Write the reactions involved in the   process.
 Answer:  Common salt : NaCl.Sodium chloride.  Ammonia : NH3 .Ammonia
Lime Stone : CaCO3.Lime stone (Calcium carbonate)
 H2O + NH3 + NaCl + CO2  -----------> NaHCO3 + NH4Cl
2NaHCO3 ---------- Heat------>  Na2CO3+ CO2+H2O
CaCO3 ----------- Heat > CO2+CaO
 CaO + H2O --------->  Ca (OH)2 
Ca(OH)2+ 2NH4Cl ------------> CaCl2 +2NH3+2H2O
 Question:  What is efflorescence? Name one compound which shows efflorescence? support your answer with reaction?
Answer:  The processes of loosing water of crystallization, when the substance is exposed to air for long time to form anhydrous or monohydric  substance is called as efflorescence.  
Na2CO3 10 H2O, Sodium carbonate deca hydrate is one example. 
 Na2CO3 , 10 H2O -------------->Na2CO3 H2O + 9H2O
Question:   why is calcium sulphate hemihydrate called ‘Plaster of Paris’ ?

Answer: Plaster of Paris gets its name from large gypsum deposits in Montmartre in Paris. We know that plaster of Paris, which is chemically calcium sulphate hemihydrate is obtained by heating gypsum. So the origin of the name 'Plaster of Paris' is the fact that the source material gypsum is found in large deposits at Montmartre in Paris
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