class seventh

CHAPTER 10
Q.1. Fill in the blanks.
I. Oxygen is 21 by volume in air.
II. Oxygen helps in burning.
III. Hydrogen was discovered by Cavendish.
IV. Hydrogen gas can be produced by the action of acids on zinc metals.
V. Carbon Dioxide is present in air only 0.3% by volume.
VI. For preparing of banaspati ghee from vegetable oil hydrogen is used.
VII. In fire extinguishers carbon dioxide.

Q.2. Tick (√) true or false.
(i) Oxygen has no effect on litmus paper. √ True / False
(ii) Hydrogen does not catch fire suddenly. True / False √
(iii) Hydrogen is lighter than air. √ True / False
(iv) Hydrogen turns blue litmus red. True / False √
(v) Carbon dioxide is used for preparation of bakery products. √ True / False

Q. 3. Encircle the correct answer from the following choice.
1. Human body consists of oxygen by mass.
a. 61%
b. 63 %
c.
65%
d. 67%
2.
Oxygen Means
a. Acid Producer
b. Base producer
c. Water producer
d. Fir producer
3. Which of the gas is necessary for respiration.
a. Nitrogen
b. Carbon dioxide
c. Hydrogen
d.
Oxygen
4. Carbon dioxide was discovered in
a.
1755
b. 1766
c. 1772
d. 1776
5. Which of the following gas is used to prepare ammonia.
a.
Hydrogen
b. Carbon dioxide
c. Oxygen
d. Chlorine
6. Which of the following gas is used in respiration by animals.
a. Hydrogen
b. Carbon dioxide
c.
Oxygen
d. Chlorine

Q. 4. Describe the laboratory preparation of oxygen
Ans:
Laboratory preparation of oxygen gas. (Fig.10.1 page 78.)

Chemical equation:
MNO2
2KClO3 2KCl + 3O2

Procedure:
Four part potassium chlorate and one part manganese dioxide is mixed and heated as shown in the figure, oxygen is collected in the gas jar.

Q. 5. What is the importance of oxygen in daily life?
Ans:
Use of Oxygen (O2):
(i) Use in respiratory.
(ii) Helps in combustion / burning
(iii) Used in welding
(iv) Astronauts, climber mountain, pilots, and deep see divers take oxygen cylinder with them.

Q.6. Give the use of carbon dioxide in daily life.
Ans:
Use of Carbon dioxide (CO2):
(i) Use by plants for photo system.
(ii) Use in making sodium hydrogen carbonate and sodium carbonate.
(iii) Used as a fire extinguisher.
(iv) It is filled in soft drinks under high pressure.
(v) Used in preparation of urea.
(vi) Used in making dry ice.

Q.7. Give the industrial uses of hydrogen, oxygen and carbon dioxide.

Use of hydrogen:
(i) Used in preparing Ammonia.
(ii) Used in preparation of Hydrochloric Acid.
(iii) Liquid Hydrogen is used as rocket fuel.
(iv) Used in conversion of oil to ghee

Use of Oxygen:
(i) Used in metallurgy
(ii) Used in preparing Sulphuric acid.
(iii) Used in preparing Nitric Acid.

Used of Carbon dioxide:
(i) Used in preparation of Sodium bicarbonate. Na(HCO3)
(ii) Used in preparation of sodium bi carbonate. Na2CO3
(iii) Used in Pepsi Industries.
(iv) Used in Preparation of Urea.
(v) Used to make Dry Ice.

CHAPTER 11

Q. 1. Fill in the blanks.
(i) the most abundant source of water is Ocean.
(ii) Hydrogen and oxygen combine in a ration of 2:1 by volume to form water.
(iii) The freezing point of water is O c0.
(iv) The presence of carbonates of magnesium makes the water hard.
(v) Salinity is the accumulation of salts in the soil.
(vi) For removal of temporary hardness of water Electricity Method is used.
(vii) Water of rains and floods raise the level of water table.

Q.2. Tick (√) true or false.
(i) Soft water has poor cleaning action True / False √
(ii) The control of water logging and salinity is not necessary. True / False √
(iii) Permanent hardness of water is due to presence of chlorides and
Sulphates of calcium and magnesium. √ True / False
(iv) Soft water is free of salts. True / False √
(v) When evaporation takes place, the salts remains in the soil and
Cause salinity. √ True / False

Q. 3. Encircle the correct answer from the following choice.
i. Temporary hardness of water is due to presence of
a. Bicarbonates of calcium and magnesium
b. Carbonates of calcium and magnesium
c. Chlorides of calcium and magnesium
d. Sulphates of calcium and magnesium
ii. Which of the following is insoluble in water.
a. Bicarbonate of calcium
b. Carbonate of calcium
c. Chloride of calcium
d. Sulphates of calcium
iii. Clark’s method is used to remove temporary hardness, which of following is not the feature of this method.
a. Lime water is added
b. Soluble carbonates remains unchanged
c. Insoluble calcium carbonates are formed
d. insoluble salt settle down
iv. In Ion Exchange Method calcium and magnesium ions exchange for
a. Sodium ion
b. Magnesium Chloride
c. Calcium Sulphates
d. Calcium Carbonate
Q.4. Differentiate between soft and hard water.
Ans:

Sr. No
Soft Water
Hard Water
I.
It gives lather with soap
It doesn’t give lather easily with soap
II.
It produces no curds
It produces lather with soap
III.
It has good cleaning action
It’s cleaning action is poor
IV.
It contains no salts
It contains some salts
V.
It is used for drinking
It is unfit for drinking.

Q.5. What are bad effects of hard water?
Ans:
Bad effects of hard water:
1 When hard water is used for drinking purposes it causes stomach disorder.
2 It has poor cleaning action hence consumption of soap or detergents is more then soft water.
3 In boiler and turbines salts deposit inside and block the pipe lines which can cause explosion
of boilers or turbines.
4The salts deposited in the boilers and turbines make the walls thick and heating efficiency reduces.

Q.6. What is water logging and salinity?
Ans:
Water logging
Means the rise in the level of water table of an area making the soil marshy.
Salinity:
Means the increase of quantity of salt in the soil.

Q.7. How temporary hardness of water is removed?
Ans:
There are two methods to remove temporary hardness.
(i) By Boiling: Water contains bicarbonates of calcium and magnesium. If boiled then these soluble salts become insoluble and settles down. Pure water is then decanted off.
(ii) Clark’s methods: In this method lime water is added and thus the soluble salts become insoluble and settles down then the soft water is decanted off.

Q.8. How permanent hardness of water is removed?
Ans:
By using washing soda (sodium Carbonate)
When washing soda is dissolved in permanent hard water, the soluble chlorides and sulphates of calcium and magnesium are converted into insoluble carbonates of magnesium and calcium. Then insoluble salts are removed by filtration or soft water is decanted.
Ion Exchange Method:
In this method water is passed through a resin and the calcium and magnesium causing permanent hardness is removed.

Q.9. How water logging and salinity can be controlled?
Ans:
Removal of water logging
(i) Deep wells are made and the water is drained off.
(ii) Special crops are cultivated which sucks the water and lower water table.
(iii) Drain channels are made.

Salinity:
(i) If soil is acidic then fertilizers like ammonia and urea used.
(ii) If soil is basic then fertilizers like gypsum are used.

CHAPTER 12

Q.1. Fill in the blanks.
(i) Air pressure increase by filling more air in a football.
(ii) Inclined plane is used to raise heavy load without lifting it.
(iii) A screw is a simple machine.
(iv) A pulley is used to lift things by pulling a rope over it.
(v) Gear is used to multiply force or to gain speed.

Q.2. Tick (√) true or false.
(i) Manometer is used to measure atmospheric pressure True / False √
(ii) A spanner works on the principle of wheel and axle. √ True / False
(iii) An inclined plane is used to multiple distances. True / False √
(iv) Gear my be used to multiple force. √ True / False


Q. 3. Encircle the correct answer from the following choice.
i. In a mercury barometer, the atmospheric pressure is nearly equal to
a. 1000 mm o fmercury
b. 760 mm of mercury
c. 750 mm of mercury
d. 76 mm of mercury
ii. A screw is an example of
a. A pulley
b. a wheel and an axle
c. A inclined plane
d. A gear
iii. Minimum number of wheels used in a wheel and axle is
a. One
b. Two
c. Three
d. Any number
iv. A gear is s system of at least two wheels
a. Having common axis
b. Of equal diameters
c. Of unequal diameters
d. One of which is fixed

Q.4. Give short answers of the following questions.

i. Which instruments is used to measure the pressure of gas in a container?
Ans: Manometer is an instrument used to measure the pressure of gas in a container.

ii. How can you make your own barometer?
Ans: Take a balloon and cut it into half, stretch it over the open end of a jar as shown in diagram (Page 95 fig 12.5). When the pressure increases, the air inside the jar will be compressed. It causes the balloon surface to move down. When the atmosphere pressure decreases the air inside the jar will expand. It causes the balloon surface to move up. By this we can note the increases and decrease of pressure.

iii. Why a wheel and axle is used?
Ans: A wheel and axle is used to lift heavy loads or to turn a body with less force such as screw driver, and steering wheel of a car.

iv. Give an example from daily life in which a pulley is used?
Ans: (i) To lift water from well
(ii) Fixed pulley is used to lift heavy loads.

v. Why do we use an inclined plane.
Ans: An incline plane is used to raise heavy load with less effort. The winding roads in hilly area. Inclined planes helpful for cars and trucks to reach to the top of the hill.

vi. Why do we use a spanner to tighten a nut?
Ans: As spanner work on the principle of wheel and axle, by means of which we can easily tighten or lose a nut.

vii. What is the principle of a screw jack?
Ans: Work on principle of screw, as we know that screw is s type of circular inclined plane. So screw jack is the combination of inclined plane and axle.

viii. What are the advantages of a gear?
Ans: Gears are used to either gain speed or increase the force.

CHAPTER 13
Q.1. Fill in the blanks
(i) Sun is the source of heat energy.
(ii) Metals are good conductor of heat
(iii) Air is a bad conductor of heat.
(iv) Sea breeze blows from sea to land.
(v) Good radiators of heat are good absorbers of heat.

Q.2. Tick (√) true or false.
(i) Condition of heat takes place by the actual movement molecules
of a substance. True / False √
(ii) Water is good conductor of heat. True / False √
(iii) Air in a room is heated by conduction. True / False √
(iv) Land breeze blows during daytime. True / False √


Q. 3. Encircle the correct answer from the following choice.
i. The number of modes of heat transfer is
a. Two
b. Only One
c. Three
d. Four
ii. Which of the following material are good conductors of heat?
a. Gases
b. Metals
c. Objects made of plastic
d. Ice and water
iii. Water is heated by
a. Conduction
b. Convection
c. Radiation
d. absorption
iv. We get heat from the sun by
a. Conduction
b. Convection
c. Radiation
d. All of them
v. We use light colored clothes in summer because they are:
a. Bad conductor of heat
b. Good absorber of heat
c. Good reflector of heat
d. Good radiator of heat

Q.4. Give a short answer of the following questions.

i. Name the various modes of transfer of heat.
Ans:
They are as follow
(a) Conduction
(b) Convection
(c) Radiation

ii. How heat reaches from hot end to a metal to its colder parts?
Ans:
Heat reaches from hot end of a metal to its colder parts by means of conduction.

iii. Why condenser pipes at the back a refrigerator are painted black?
Ans:
It is because by this it becomes good emitters of heat.

iv. Name two good conductors and two insulators.
Ans:
Good Conductor:
Copper, Aluminum

Insulators:
Glass, Wood

v. Give one application of good conductor and one of insulator
Ans:
Good Conductor
Copper is used in making electric wires.

Insulators
Handles of cooking utensils are made so cooking becoming easy.

vi. Describe an activity for heat transfer by convention?
Ans:
Take water in a glass bath. Put few crystals of pinky or ink drops in it. Note the spreading mode of color in water. Put the both on flame we will observe the convection mode of heating. i.e. hot water molecules will rise to the top while from the top the colder molecules will move toward the bottom.

vii. Explain the causes of land and sea breezes.
Ans:
During day time hot air from the land rises up and cold air from the sea comes to replace the gap, while during night, hot air above sea rises up and cold air from land blows forwards towards the sea to cover the gap.

viii. Which types of surfaces are good absorber and good radiator of heat?
Ans:
Dull, black and rough surfaces are good absorber and good radiator of heat.

ix. How do we get heat from the sun without the presence of any medium?
Ans:
All it is due to radiation mode of transfer of heat.

x. How transfer of heat is minimized in thermos flask?
Ans:
Transfer of heat is minimized by putting proper insulations like glass, vacuumed system is also made.
CHAPTER 14


Q.1. Fill in the blanks.
(i) The image formed by a plane mirror is laterally Opposite.
(ii) The image formed by a plane mirror is same size.
(iii) Shaving mirror is a concave mirror.
(iv) A security mirror used in departmental sore is a convex mirror.
(v) A kaleidoscope is formed using two or more rectangular mirror.

Q.2. Tick (√) true or false.
(i) A real image can be formed by a plane mirror. True / False √
(ii) A concave mirror has a large field of view. True / False √
(iii) A convex mirror has a large field of view. √ True / False
(iv) The image formed by a convex mirror is always virtual. √ True / False


Q. 3. Encircle the correct answer from the following choice.
i. In a plane mirror, the image size as compared to the object size is
a. half
b. Double
c. Same
d. Not fixed
ii. Which of the following is a concave mirror?
a. A dentist’s mirror
b. Back view mirror
c. Security mirror
d. Mirror used at blind corners
iii. Which of the following is a convex mirror?
a. A dentist’s mirror
b. Shaving mirror
c. Security mirror
d. Make up mirror
iv. Which of the following can produce real image?
a. Plane mirror
b. Concave mirror
c. Convex mirro
d. None of them.
v. Which of the following devices is used in submarine?
a. Kaleidscope
b. Microscope
c. Periscope
d. None of them

Q.4. Give short answers of the following questions.



(i) What are the characteristics of an image formed by a plane mirror?
Ans:
a. The image is formed as much behind the mirror as much in the object in front the mirror
b. Image formed in the mirror is upside and of the same size as that the object.
c. Image is inserted from left to right. Left side of the object appears to be the right and right side appears to be the left.

(ii) What is a concave mirror? Draw a ray diagram to form a real image of an object by a concave mirror.
Ans:
It is a curved mirror whose outer surface is polished and painted is called a concave mirror. Diagram fig. 14.5 page 111

(iii) Draw a ray diagram to form a virtual image of an object by a concave mirror.
Ans:
Diagram fig 14.6 page 112


(iv) What is a convex mirror? Give two of its applications in our daily life.
Ans:
Convex Mirror:
A special mirror whose inner surface is polished and painted is called convex mirror.
Uses of Convex mirror:
a. It is used at blind corners of roads for drivers to see the vehicles coming from opposite side.
b. Used in cars as back view mirror

(v) What is kaleidoscope?
Ans:
A kaleidoscope shows beautiful colored pattern formed by multiple reflections of loose pieces of colored objects. As we rotate it, the patterns changes.

(vi) What is periscope? Give its two applications.
Ans:
A periscope is an instrument made to see things above the level of viewers or when it is not safe to see objects directly.
USES: (i) it is used in submarines
(ii) It is used in tanks.