TS 7th Class Science Important Questions 17th Lesson Changes Around Us

These TS 7th Class Science Important Questions 17th Lesson Changes Around Us will help the students to improve their time and approach.

TS 7th Class Science Important Questions 17th Lesson Changes Around Us

Question 1.
Write the appropriate period of time after which the following changes are repeated.
Rising of the polar star, change of seasons, change of greenery in the fields of
cultivation, changes in lengths of shadows and appearance of full moon.
Answer:

S. No.	Name of the change	Approximate period of time of repetition
1.	Rising of the polar star	24 hours
2.	Change of seasons (four seasons)	1 year
3.	Change of greenery in the fields	1 year
4.	Change in lengths of shadows	1 day
5.	Appearance of full moon	30 days
6.	Appearance of new moon	30 days

Question 2.
What is ‘rust’ ? What type of change is ‘rusting’ physical or chemical? Is it  reversible?
Answer:

• Rust is hydrated Iron (III) oxide.
• Rusting is a chemical change.
• The change is irreversible.

Question 3.
How can we prevent browning of cut vegetables and fruits?
Answer:
The following methods are useful to prevent browning of cut vegetables and fruits.

• Keep the cut vegetables in cold water.
• Small quantities of acids like lemon juice or vinegar may also be added to that water.
• The surface of the cut fruits is rubbed with lemon juice.
• Ascorbic acid (vitamin C) added to that water.

Question 4.
What is crystallisation?
Answer:
The process of separating a soluble solid from the solution by heating or evaporating is called crystallisation.

Question 5.
Explain the following chemical changes.
a. A piece of magnesium wire is burnt in air and the ash is tested.
b. An iron nail is dropped in a beaker containing acidified copper sulphate solution.
c. Baking soda is added to vinegar.
d. Carbon dioxide gas is bubbled through lime water.
Answer:
a. A piece of magnesium wire is burnt in air and the ash is tested:

• The “Mg” wire burns with a white dazzling light. (The dazzling is due to ultra violet rays in it. This light is harmful to our eyes.)
• A white ash is formed.
  Magnesium + Oxygen → Magnesium oxide (ash)
• The ash is shaken with a little water. It dissolves partly.
• This solution turns red litmus paper, blue. So it is a basic solution. It is called magnesium hydroxide.
• So magnesium oxide is called a ‘basic oxide’.

b. An iron nail is dropped in a beaker containing acidified copper sulphate solution.
When an iron nail is kept in blue copper sulphate solution for some time,

• Iron nail gets a red coating of copper.
• blue solution changes to light green.
  This solution is, iron (II) sulphate (or ferrous sulphate) solution.
  This chemical change is called, a ‘displacement’ reaction.

Question 6.
What things are likely to occur, during a chemical change 7
Answer:
In addition to the formation of new products, the following changes may also take place in a chemical change.

• Heat, light or any other radiation may be given out or absorbed.
• Loud sound may he produced.
• A change in smell may take place or a new smell may be produced.
• A colour change may take place.
• A change in state may occur.

Question 7.

What type of change is it? Is it reversible ? If so. how?
Answer:
1) Ice slowly melts and becomes water. On further heating, water changes to steam.
This is a physical change. No new substance is formed.
ii) The change is reversible.
If we reduce the temperature, the water vapour changes back to water.
When the temperature is further reduced, it changes to ice.

Question 8.
What happens, when copper utensils are exposed to air?
Answer:
When copper utensils are exposed to moist air, a greenish coating forms on them. This is formed when copper reacts with oxygen, water vapour and carbon dioxide, present in air. Chemically, this greenish substance is called, basic copper carbonate (verdigris).

Question 9.
What question you would pose to your teacher about changes around us?
Answer:

• Why changes occur around us?
• Why should we depend on changes in the nature?
• What would happen if changes do not occur?
• How changes in the nature influence us?

Question 10.
Write the possible changes you notice for each case and put (✓) in the appropriate column.
Answer:

Question 11.
What are the changes (any three) observed, when small pieces of wood, paper and cotton are burnt?
Answer:
When these are burnt,

• new materials are formed. The product is a black powder.
• the shape and size of the new material is different.
• the change is irreversible.
  So the changes are chemical changes.

Question 12.
Why some fruits get a brown layer on the surface, when cut?
Answer:
Some fruits and vegetables when cut, react with oxygen in the air. Then they get a brown layer on them.

Question 13.
How to prepare a ‘saturated’ solution of copper sulphate ?
Answer:

• Take about 50 ml of water in a beaker.
• Take some copper sulphate solid and powder it.
• Add a small quantity of this solid to the water in the beaker.
• Stir the solution with a glass rod till the solid dissolves.
• Add some more of the solid and stir well.
• Continue adding the solid in small lots and continue stirring. Most of the solid dissolves.
• Now some solid remains at the bottom of the beaker, without dissolving.
• This solution is called, a ‘saturated solution’ of copper sulphate.
  The solution which cannot dissolve any more of the solid is called a ‘saturated solution’.

Question 14.
What happens, when a hot saturated solution (called, super saturated solution) of copper sulphate is allowed to cool in an evaporating dish ?
Answer:
Fine blue crystals of copper sulphate form, at the bottom of the dish.

Question 15.
Write some daily activities you collected from farmers, houses and nearby small industries about physical and chemical change?
Answer:

• Farmers use chemical fertilizers in the crop field. Those fertilizers mix with water. It is a chemical change.
• Cook in the kitchen prepares payasam. Payasam preparation is a chemical change.
• Priest in the temple offers prayers with camphor. Camphor evaporates. It is a chemical change.
• Sickles are prepared by vadrangi. It is a physical change.

Question 16.
Think about the following changes and decide whether they are physical or chemical changes. Write the type of change and reasons for that in the table.
Answer:

Question 17.
Why are gold and silver often used in making ornaments?
Answer:
Even if these two metals are exposed to air for a long time, they do not change colour or get rusted. It means, these metals are resistant to corrosion. This is the reason why we use them in making ornaments.

Question 18.
Changes in the nature are amazing natural phenomena. Give your answer.
Answer:
Man depends on changes in the environment. Without change in environment, there is no life on the Earth. Eg: Without cooking some materials, we can’t eat them. Even changes in the baby during pregnancy give perfect shape and structure.

Choose the correct answer:

I. Conceptual Understanding

Question 1.
A periodic change ( )
A) A physical change
B) A chemical change
C) A reversible change
D) Sunrise
Answer:
D) Sunrise

Question 2.
A physical change ( )
A) Solidification of ghee
B) Melting of ice
C) Inflate a balloon
D) All these
Answer:
D) All these

Question 3.
A chemical change ( )
A) Charring of sugar
B) Rusting of iron
C) Black coating on silver articles
D) All of these
Answer:
D) All of these

Question 4.
The incorrect statement among the following. Burning of camphor is similar to ( )
A) burning of magnesium
B) burning of wood
C) breaking of glass
D) rusting of iron
Answer:
C) breaking of glass

Question 5.
When carbon dioxide gas is bubbled through lime water, the following changes are observed. ( )
A) Lime water turns milky
B) Calcium carbonate is formed
C) Water is formed
D) All of them
Answer:
D) All of them

Question 6.
Which of the following substances show chemical change on heating? ( )
A) CuCO₃
B) Ice
C) ZnO
D) lodine
Answer:
A) CuCO₃

Question 7.
Which of the following turns lime-water milky? ( )
A) O₂
B) CO₂
C) ZnO
D) MgO
Answer:
B) CO₂

Question 8.
This metal is used in galvanization. ( )
A) Copper
B) Silver
C) Zinc
D) Iodine
Answer:
C) Zinc

Question 9.
CuCO2 → ……………….. +CO₂ ( )
A) CuO
B) CuCO₂
C) CuO₄
D) O₂
Answer:
A) CuO

Question 10.
Magnesium + …………….. → Magnesium oxide. ( )
A) Water
B) Oxygen
C) Carbon dioxide
D) Hydrogen
Answer:
B) Oxygen

II. Asking Questions and Making Hypothesis

Question 11.
Find out the odd one against physical change. ( )
A) Burning candle
B) Melting rice
C) Coconut oil in winter
D) Burning paper
Answer:
D) Burning paper

Question 12.
If galvanization technique was not invented, the iron material would have been remained in ( )
A) rusting state
B) over reacted
C) no change
D) B and C
Answer:
A) rusting state

Question 13.
vinegar + baking soda : carbon dioxide : : carbon dioxide + lime water ? ( )
A) calcium oxide
B) calcium carbonate
C) calcium nitrate
D) calcium hydrate
Answer:
B) calcium carbonate

Question 14.
On heating water, it ( )
A) melts
B) fuses
C) evaporates
D) solidifies
Answer:
C) evaporates

Question 15.
Browinish red spots that are observed on the iron nails is … ( )
A) rust
B) dust
C) galvanization
D) vulcanisation
Answer:
A) rust

Question 16.
What did you observe while burning the magnesium ribbon? (  )
A) Red coloured flame
B) Solid waste
C) Brilliant white dazzling light
D) Rust
Answer:
C) Brilliant white dazzling light

Question 17.
When you kept iron nail in the blue coloured copper sulphate solution what changes occurred in the solution ? ( )
A) Brown colouration
B) Green colouration
C) Black colour
D) White colour
Answer:
B) Green colouration

Question 18.
What change you observed in cut apple? ( )
A) Permanant change
B) solid change
C) physical change
D) chemical change
Answer:
D) chemical change

Question 19.
What type of change you observed iii recharge batteries? ( )
A) chemical change
B) physical change
C) no change
D) temporary change
Answer:
A) chemical change

Question 17.
When you kept iron nail in the blue coloured copper sulphate solution what changes occurred in the solution ? ( )
A) Brown colouration
B) Green colouration
C) Black colour
D) White colour
Answer:
B) Green colouration

Question 18.
What change you observed in cut apple? ( )
A) Permanant change
B) solid change
C) physical change
D) chemical change
Answer:
D) chemical change

Question 19.
What type of change you observed in recharge batteries? ( )
A) chemical change
B) physical change
C) no change
D) temporary change
Answer:
A) chemical change

IV. Information Skills and Projects

Question 20.
Give one example you collected from your kitchen regarding chemical change. ( )
A) Preparing curry
B) Preparing idly
C) Cooking rice
D) All the above
Answer:
D) All the above

Question 21.
What changes occur in firing crackers on Deepavali festival?
A) Chemical change
B) Physical change
C) Both physical and chemical
D) None of the above
Answer:
A) Chemical change

Question 22.
What would you see in the nature of coconut oil during winter season?
A) Coconut oil evaporates
B) Coconut oil melts ( )
C) Coconut oil solidifies
D) A and B
Answer:
C) Coconut oil solidifies

V. Appreciation and Aesthetic Sense and Values

Question 23.
People use turmeric with lime water as parani on some occasions. It is a good example for chemical change. On which occasions usually it is done? ( )
A) Weddings
B) Festivals
C) House openings
D) All the above
Answer:
D) All the above

VII. Application to Daily Life and Concern to Bio Diversity

Question 24.
The chemical change you enjoy with. ( )
A) Rusting of iron
B) Redness of mouth with killi (paan)
C) Formation of carbon dioxide
D) Formaton of dust
Answer:
B) Redness of mouth with killi (paan)

Question 25.
Children enjoy Diwali fire works. Women light the pramidalu (oil containing earthern plate lamps). What change occurs in burning pramidalu. ( )
A) Chemical change – evaporation of oil
B) Physical change – evaporation of oil
C) Physical change – burning of wick
D) Both physical and chemical change
Answer:
A) Chemical change – evaporation of oil