CHEMISTRY ASSIGNMENT No 1
CLASS-9
ATOMS AND MOLECULES
Q1 State law of conservation of mass.
Ans The mass can neither be created nor destroyed in a chemical reaction.
Q2 State law of constant proportion.
Ans A pure chemical compound always consists of the same elements that are combined
together in a fixed proportion by mass.
Q3 Write name and symbol of first 20 elements of the periodic table.
Ans Atomic number Name of the element Symbol
1 Hydrogen H
2 Helium He
3 Lithium Li
4 Beryllium Be
5 Boron B
6 Carbon C
7 Nitrogen N
8 Oxygen O
9 Fluorine F
10 Neon Ne
11 Sodium Na
12 Magnesium Mg
13 Aluminium Al
14 Silicon Si
15 Phosphorous P
16 Sulphur S
17 Chlorine Cl
18 Oxygen O
19 Potassium K
20 Calcium Ca
Q4 Define atomic mass unit.
Ans The mass of one twelfth (1/12) of the mass of one atom of carbon taken as 12.
Q5 What are molecules?
Ans Molecules represents a group of two or more atoms(same or different) chemically
bonded to each other and held tightly by strong attractive forces.
Molecules are of two types
(a) Molecules of elements
(b) Molecules of compound
Q6 What do you mean by molecular mass?
Ans The average relative mass of the molecule as compared to the mass of carbon takrn
as 1u.
Q7 Write the relationship between number of moles and atomic mass.Ans Number of moles=givenmass/gram atomic mass
Q8 Why are chemical reactions according to law of conservation of mass?
Ans In all chemical reactions, there is only exchange of reactants taking place when
products are formed. Since there is no loss or gain of mass,the chemical reactions are
according to law of conservation of mass.
Q9 What is basic difference between atoms and molecules?
Ans Atoms except those of noble or inert gas elements cannot exist of their own.
However ,all molecules can have independent existence.
Q10 The atomic mass of an element is in fraction .What does it mean?
Ans If the atomic mass of an element is in fraction, this mean that it exists in the form of
isotopes. The atomic mass is the average atomic mass and is generally fractional.
Q11 What is the difference between the mass of molecule and molecular mass?
Ans Mass of a molecule is that of a single molecule also known as its actual mass. But
molecular mass is the mass of Avagadro’s number of molecules.
Q12 Where do we use the words mole and mol?
Ans In the text part we use the word mole while as a unit ,we call it mol.
Q13 How many moles are present in 11.5 g of sodium?
Ans Gram atomic mass of Na =23g
23g of Na represents = 1 mol
11.5g of Na represents= (1mol)*(11.5g)/23.5g)=0.5 mol
Q14 Explain why the number of atoms in one mole of hydrogen gas is double the
number of atoms in one mole of helium gas?
Ans Hydrogen gas is a diatomic in nature(H2) while helium gas is monoatomic (He).As a
result, the number of atoms in one mole of hydrogen(2*NA )are expected to be double as
compared to number of atoms in one mole of helium(NA)
Q15An element Z forms an oxide with formula Z2O3. What is its valency?
Ans Valency of Z=3 Q16
The valency of an element A is 4 . Write the formula of its oxide.
Ans The formula of its oxide is A2O4 or AO2.
Q17 An element X has valency 3 while the element Y has valency 2.Write the formula
of the compound between XandY .
Ans X2Y3
Q18 What are ions?
Ans Ions are of two types
(a) cations - positively charged
(b) anions - negatively charged
Q19 Which postulate of Dalton’s Atomic theory is the basis of law of conservation of
mass?
Ans “ Atoms can neither be created nor destroyed during a physical or a chemical
change”
Q20 Write the formulae of sodium oxide and aluminium chloride
Ans Sodium oxide = Na2O
Aluminium chloride =AlCl3
Q21 Find out the ratio by mass of the combining elements in the following compounds(a) MgCO3 (b) CH3OH (c) CaCl2
Ans21
(a) MgCO3 ------ Mg :C:O = 24:12:48 = 2:1:4
(b) CH3OH ------ C : H : O =12:4:16 =3:1:4
(c) CaCl2 ----------- Ca :Cl = 40:71
Q22 Define atomicity of the molecule.
Ans Atomicity of the molecule is the number of atoms present in the molecule.
Q23 What is the atomicity of oxygen,ozone,neon and sulphur?
Ans Oxygen O2 = 2
Ozone O3 = 3
Neon Ne =1
Sulphur S8 =8
Q24 What is wrong with the statement '1 mol of hydrogen'
Ans The statement is not correct.We must always write whether hydrogen is in atomic
form or molecular form. The correct statement is :
1mole of hydrogen atoms or one mole of hydrogen molecules .
Q25 The atomic mass of an element is in fraction. What does it mean?
Ans If the atomic mass of an element is in fraction,this mean that it exists in the form of
isotopes.The atomic mass is the average atomic mass and is generally fractional.
Gravitation Assignment
Q 1. A body is fully immersed in water to a depth of 2m,
4m and then 5 m, in turn. Will the loss in its weight be equal or different in
three cases? If different, in which case will it be least?
Q2a) State Archimedes Principle. Write its two
applications.
b) Define
the term Buoyancy. How does the surface area of an object effects buoyant force?
Q 3Explain, with the help of an example the difference
between the terms. Thrust and
Pressure. Which one of the two has same SI unit as that
of Force?
Q4 The volume of a body of mass 50 g is 20 cm3. If the density of water is
taken as 1 gcm-3, will the substance float or sink in water? Why?
2. The buoyant force on a body acts in a
a) vertically downward direction
b) vertically upward direction
c) horizontal direction
d) direction between the horizontal and the vertical
3. The force acting normally on a surface is called
a) pressure b) Thrust c) Force d) Balanced
4. Mark the statements true (T) or false (F)
a) The pressure at all points in a liquid at the same horizontal plane is equal.
b) Pascal and N/m2
represent the same unit.
c) Pressure has magnitude as will as direction.
5. 1 bar = _____ Pa
a) 105 b) 10-5
c) 103 d) 10-3
Section B
1. Define pressure at a point.
2. State Archimedes principle.
3. Why is it easier to swim in sea water than in fresh water?
4. Does a liquid press an immersed body from all sides?
Section C
1. A body of volume 50 cm3
is completely immersed in water. Find the force of
buoyancy on it.
2. A block weighing 1 kg is in the shape of a cube of length 10 cm. It is kept on a
horizontal table. Find the pressure on the portion of the table where the block is
kept.
3. A bottle weighs 30 g when empty, 53.4 g when filled with a liquid and 48 g when
filled with water. Calculate the density of the liquid. Given, density of water at 40C
= 1000 kg/m3
.
4. A metallic sphere of radius 2.0 cm is completely dipped in water. Find the force of
buoyancy on it.
5. A cubical block of copper is dipped completely in water. Each edge of the block is
1cm in length. Find the buoyant force acting on the cube.
21.
State 21.
State
CLASS—IX
Physics Assignment
WORK, ENERGY AND
POWER
1. Under what conditions work is said to be done?
2. Derive the formula for work done by a constant force
3. Give few examples where energy is possessed by a body due
to its change in shape.
4. State and prove the law of conservation of energy.
5. Is it possible that force is acting on a body but still
work done is zero? Explain.
6. A rocket of mass3x106 kg takes off from a launching pad
and acquires a vertical
velocity of 1km/s at an altitude of 25 km. calculate (a) the
potential energy and (b) the
kinetic energy. (g = 9.8m/s2)
7. If a man lifts a load up with the help of a rope such
that it raises the load of mass 50kg
to a height of 20m in 100 sec. Find the power of man
8. A ball is dropped from a height of 5m. Find the velocity
of the ball just before it
reaches the ground. Do you require the value of mass to find
the velocity?
9. Two persons A and B do same amount of work. The person A
does that work in t1sec
and the person b in t2sec. Find the ratio of power delivered
by them.
10. Why do our hands become warm when rubbed against each
other? Explain.
11. The kinetic energy of a body of mass 15 kg is 30J. What
is its momentum?
12. Give an example for each of the following energy
conversion: (1) electrical energy to
kinetic energy. (2) Chemical energy to electrical energy (3)
sound energy to electrical
energy
13. Two bodies have same momentum. Which will have greater
kinetic energy- heavier
body or lighter body?
14. An electric bulb of 60w is used for 6h per day
.Calculate the units of energy
consumed in one day by the bulb.
15. A boy of mass 50kg runs up to a stair case of 45 steps
in 9s. If the height of a step is
15cm, find his power. (g= 10m/s2
)
16. Two particles of masses 1g and 2g have equal momentum.
Find the ratio between
their kinetic energies?
17. What will be the work done by the string, when a stone
is tied to a string and whirled
in a circle?
18. A locomotive exerts a force of 7500N and pulls a train
through 1.5 km. How much
work is done by locomotive?
19. What work a boy of mass 50kg will do in order to
increase running speed from
9km/h to 18km/h.
20. The speed of a moving body is halved. What is the change
in its K.E.?
hilly road.(2) a stone projected vertically upward returns
22. When we cut a log of wood with a saw it becomes warm,
why?
23. If an electric iron of 1200W is used for 30 minutes
everyday, find electric energy
consumed in the month of April. CLASS—IX
Physics Assignment
WORK, ENERGY AND
POWER
1. Under what conditions work is said to be done?
2. Derive the formula for work done by a constant force
3. Give few examples where energy is possessed by a body due
to its change in shape.
4. State and prove the law of conservation of energy.
5. Is it possible that force is acting on a body but still
work done is zero? Explain.
6. A rocket of mass3x106 kg takes off from a launching pad
and acquires a vertical
velocity of 1km/s at an altitude of 25 km. calculate (a) the
potential energy and (b) the
kinetic energy. (g = 9.8m/s2)
7. If a man lifts a load up with the help of a rope such
that it raises the load of mass 50kg to a height of 20m in 100 sec. Find the
power of man
8. A ball is dropped from a height of 5m. Find the velocity
of the ball just before it
reaches the ground. Do you require the value of mass to find
the velocity?
9. Two persons A and B do same amount of work. The person A
does that work in t1sec and the person b in t2sec. Find the ratio of power
delivered by them.
10. Why do our hands become warm when rubbed against each
other? Explain.
11. The kinetic energy of a body of mass 15 kg is 30J. What
is its momentum?
12. Give an example for each of the following energy
conversion: (1) electrical energy to kinetic energy. (2) Chemical energy to
electrical energy (3) sound energy to electrical energy
13. Two bodies have same momentum. Which will have greater
kinetic energy- heavier body or lighter body?
14. An electric bulb of 60w is used for 6h per day
.Calculate the units of energy
consumed in one day by the bulb.
15. A boy of mass 50kg runs up to a stair case of 45 steps
in 9s. If the height of a step is 15cm, find his power. (g= 10m/s2)
16. Two particles of masses 1g and 2g have equal momentum.
Find the ratio between
their kinetic energies?
17. What will be the work done by the string, when a stone
is tied to a string and whirled in a circle?
18. A locomotive exerts a force of 7500N and pulls a train
through 1.5 km. How much work is done by locomotive?
19. What work a boy of mass 50kg will do in order to
increase running speed from
9km/h to 18km/h.
20. The speed of a moving body is halved. What is the change
in its K.E.?
hilly road.(2) a stone projected vertically upward returns
22. When we cut a log of wood with a saw it becomes warm,
why?
23. If an electric iron of 1200W is used for 30 minutes
everyday, find electric energy
consumed in the month of April.
ASSIGNMENT ON SOUND
Q1. Which sound has a higher pitch, guitar or car horn?
Q2. Name three animals which can hear ultrasonic
vibrations.
Q3. How are the
wavelength and frequency of a sound related to its speed?
Q4. Why sound wave is called a longitudinal wave?
Q5. Frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Q6. What is an echo?
Q7.What do waves transport - matter or energy?
Q8. What is a wave?
Q9. Which characteristics of the sound help us to
identify a person by his voice if he is sitting in a dark room?
Q10. If the amplitude of a wave is doubled, what will be
the effect on its loudness?
2 Marks Questions
Q11. Which wave property determines a) loudness, b)
Pitch?
Q12. Why are the ceilings of concert halls curved?
Q13. How is ultrasound used for cleaning?
Q14. Sound is produced due to a vibratory motion, then
why a vibrating pendulum does not produce sound?
Q15. A sound produces 20 crests and 20 troughs in 0.4
sec. Find the frequency of the wave.
Q16. Why sound waves are called mechanical waves?
3 Marks Questions
Q17. How is sound produced in school bell?
Q18. Bats have no eyes then how do they catch their prey?
Q19. What is SONAR?
Q20. Write three uses of multiple reflection of sound.
3 Marks Questions (Numerical)
Q21. Calculate the wavelength of a sound whose frequency
is 220 Hz and speed is 440 in a given medium.
Q22. A body is vibrating 6000 times is 1 minute. If the
velocity of sound in air is 360 m/s, find
(i) Frequency in Hz (ii)
wavelength of sound.
Q23. A stone is dropped from a 500 m tall building into a
pond. When is sound splash heard? Given g =10 m/s2 , speed of sound = 340
m/s.
Q24. An echo is heard in 3 sec after the emission of
sound. If speed of sound in air is 342 m/s, what is the distance of the
reflecting surface from the source?
M.C.Q. (1 Mark each)
Q25. For reflection of sound wave, we need -
A. A polished mirror
B. A large size, opaque reflecting surface
C. A concave surface
D. A glass plate
Q26. The speed of sound in air is -
A. Less than in solids & liquids
B. Same as that in solids & liquids
C. Greater than in solids and liquids
D. None of these
Q27. We can sense a compression in a spring if
A. Turns are close together
B. Neither closes nor apart
C. Turns are further apart than normal
D. None of these
Q 28. When sound is allowed to fall normally on the
reflecting surface, the angle at which the intensity of sound will be maximum
is:
A. 600
B. 900
C. 300
D. 00
Q29. The mechanical wave is
A. Sound Wave
B. Microwave C. Radio Wave D.
Light Wave
Q 30. Sound wave cannot pass through
A. Metals
B. Water
C. Air
D. Vacuum
Q31. The persistence of sound is an auditorium is the
results of
A. Single reflection of sound
B. Repeated reflection of sound
C. Repeated refraction of sound
D. Vibration of object placed in an auditorium
Q32.A wave set up a single disturbance of short duration
is called
A. pulse
B. Sound Wave
C. Wave
D. None of these
Q33. To determine the velocity of a pulse propagated
through a stretched slinky
A. A slight jerk is given to the slinky
B. No jerk is given to the slinky
C. Sharp jerk is given to the
slinky
D. None of these.
Q34. The distance x in below diagram is-
A. B.
2 C.
3 /2
D. /2
Q35. Two sounds of same pitch and loudness differ in
A. Tone
B. Note
C. Quality
D. All of these
19 comments:
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