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Class 7 Science Chapter 5 Changes Around Us Physical and Chemical Extra Questions
Class 7 Science Chapter 5 Extra Questions on Changes Around Us Physical and Chemical
Changes Around Us Physical and Chemical Class 7 Very Short Question Answer
Question 1.
Name two changes occurring over the years due to human activity and have a long-term environment impact.
Answer:
(a) Atmospheric pollution
(b) Combustion of fuels.
Question 2.
Identify the change that takes place when sugar is dissolved in hot water to prepare concentrated sugar syrup.
Answer:
Physical change (Reversible)
Question 3.
Name the property that is not changed in a physical change.
Answer:
Chemical composition of the substance.
Question 4.
What happens when you blow air into the glass tumbler, containing lime water?
Answer:
Lime water turns milky on blowing air (air rich in CO2) into lime water.
Question 5.
Calcium hydroxide (Lime Water) + Carbon dioxide → X (Insoluble substance) + Water. Identify ‘X’.
Answer:
X is Calcium Carbonate (Insoluble white substance).
Changes Around Us Physical and Chemical Class 7 Short Question Answer
Question 1.
Rusting is undesirable change. Justify.
Answer:
Rusting is destruction of iron particles. It causes loss to life and property. Hence it is an undesirable change.
Question 2.
Why do we say “Decomposition of food can be very useful”?
Answer:
Decomposition of food is very useful as it converts food waste into organic compost.
Question 3.
How do temperature changes, growing roots of trees etc. in rocks result in the formation of soil?
Answer:
Temperature changes, growing of roots etc. within the cracks in the rocks break them (large rock pieces) into smaller pieces by the process called as weathering.
Question 4.
Because chopped vegetables cannot return to their original size and shape. Why?
Answer:
It is irreversible physical change.
Question 5.
What are sediments? Is formation of sediment a physical change?
Answer:
Heaps of sand, soil and stones lying at the base of mountains are called sediments.
Yes, formation of sediment is a physical change.
Changes Around Us Physical and Chemical Class 7 Long Question Answer
Question 1.
(a) What do you mean by chemical change?
(b) What do you observe on focusing sunrays using a magnifying glass?
(c) What type of change is it? How do you explain the change?
Answer:
(a) Chemical change is a change in which one or more new substances are formed due to chemical reaction alongwith production of heater light.
(b) We observe that paper emits smoke and catches fire.
(c) It is a chemical change. Focusing sunrays heats the paper. The temperature of the paper increases. It becomes hot and starts burning.
Question 2.
Define Combustion. What are three essential conditions of combustion process to occur? Identify the type of change. Why is it called so? Explain with example.
Answer:
Combustion is a chemical reaction in which a substance reacts with oxygen and produces new substances along with evolution of heat and light.
There are three essential conditions for combustion process to occur:
(i) A combustible substance (fuel)
(ii) Oxygen
(iii) Ignition temperature
Combustion is a chemical change as new substances with new properties are formed along with evolution of heat and light. Burning of magnesium ribbon is an example of combustion process. New substance Magnesium oxide (white powder) is produced along with heat and light.
Question 3.
Represent the following in the form of Word Equation:
(a) Burning of Magnesium in air produces white powder of Magnesium oxide and heat and light.
(b) Vinegar and Baking soda react chemically to produce carbon dioxide and other substances.
(c) Carbon dioxide combines with lime water and produces white inso¬luble substance calcium carbonate and water.
Answer:
(a) Magnesium (Ribbon) + Air (Oxygen) → Magnesium Oxide (white powder) + Heat + Light
(b) Vinegar + Baking Soda → Carbon dioxide + Other substances
(c) Carbon dioxide + Lime Water → Calcium Carbonate (insoluble substance) + Water
Question 4.
What kind of change is shown by tearing of paper?
Answer:
This is a physical change that cannot be reversed as composition of the paper does not change, only appearance (size, shape, etc.) changes.
Question 5.
Give an example of a chemical reaction for each of the following:
(a) Change in color is observed.
(b) A gas is evolved.
(c) Sound is produced.
Answer:
(a) Formation of rust. Colour of Iron nail changes from grey to reddish brown during rusting in moist air.
(b) Reaction between vinegar and baking soda evolves carbon dioxide along with formation of other substances.
(c) Burning of crackers.
Changes Around Us Physical and Chemical Class 7 Case Based Questions
I. The collapse of bridges is attributed to corrosion of iron components of the bridges. Corrosion of iron is called rusting. Two essential conditions of rusting are:
- Presence of air
- Presence of moisture in the atmosphere.
Rusting is the harmful effect of oxidation of metals. In the absence of any one of the conditions of rusting either air or moisture, rusting will not take place.
Rust is chemically Iron oxide, is the new substance formed during rusting.
Answer the following questions:
Question 1.
What is chemical composition of rust?
Answer:
Rust is Iron Oxide.
Question 2.
“Rusting is a chemical change.” Justify.
Answer:
It is the corrosion of Iron in which a new substance Iron oxide (reddish brown) is formed with different properties them iron.
Question 3.
Why is corrosion considered as undesirable change?
Answer:
Corrosion weakens the iron bridges, buildings, machine parts due to the formation of flaky brown substance (Iron oxide). It is the harmful effect of the chemical change. It causes harm to life and property.
Question 4.
What are the two essential conditions necessary for rusting to occur?
Answer:
- Presence of Oxygen (air)
- Presence of Water (moisture)
Changes Around Us Physical and Chemical Extra Questions for Practice
Very Short Answer Type Questions
Question 1.
Define physical change.
Question 2.
Give an example of chemical change.
Question 3.
Write an example of reversible physical change.
Question 4.
Give an example of irreversible physical change.
Short Answer Type Questions
Question 1.
What is the difference between physical and chemical changes?
Question 2.
Write two observations to identify a chemical change.
Question 3.
Is rusting of iron a chemical change?
Question 4.
How will you test the presence of carbon dioxide gas?
Question 5.
State the reason: Curdling of milk is a chemical change.
Long Answer Type Questions
Question 1.
What is weathering? How does weathering lead to formation of soil? Identify the type of change shown by weathering process.
Question 2.
Some changes may be desirable in some situations and may be undesirable in other situations. Explain with example.
Question 3.
Name some Natural changes that occur over the years due to human activity. Discuss its long term environmental impact.
Case/Source Based Question
I. Amit, Raju and Nikhil took— three test tubes each and labelled them as A, B and C respectively.
II. Amit took Iron nails and copper sulphate solution (blue) in test tube
A. After some time he found that blue colour copper sulphate solution turns green due to formation of ferrous sulphate.
III. Raj added water and copper sulphate (blue) solution to test
B. He found that blue colour of the copper sulphate solution remains same.
IV. Nikhil took added baking soda and vinegar in test tube C. He found the brisk effervescence of a gas.
Now Answer the following question.
Identify the type of change in Test tube A, Test tube B, Test tube C.
Question 1.
Write two observations from the above activity that show chemical reaction has occurred.
Question 2.
Write the word equation for reaction taking place in test tube A.
Question 3.
Name the gas evolved in test tube C.
Question 4.
How will you test the presence of the gas in test tube C?
Multiple Choice Questions (MCQs)
Choose the correct option in the following questions:
Question 1.
A chemical change involves:
(a) Change in colour only
(b) Formation of insoluble substance
(c) Evolution of gas
(d) All of the above
Question 2.
Fermentation of grapes is an example of:
(a) Chemical change only
(b) Desirable and chemical change
(c) Physical and chemical change
(d) Physical change only
Question 3.
Rocks undergo physical and chemical changes to form soil due to:
(a) Soil erosion
(b) Weathering
(c) Bioluminescence
(d) Combustion
Question 4.
Landslides is an example of:
(a) Physical change only
(b) Chemical change
(c) Both physical and chemical change
(d) None of the above
Question 5.
Originally black coloured BASALT rock changes chemically to produce red coloured layer due to the presence of
(a) Iron oxide
(b) Calcium carbonate
(c) Lime water
(d) Carbon dioxide
Assertion-Reason Questions
Directions: Each of the questions (i) and (ii) contain two statements – first ‘Assertion’ and second ‘Reason’. Select the correct answer to these questions from the codes (a), (b), (c) or (d) as given below:
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true and Reason is NOT the correct explanation of Assertion.
(c) Assertion is true and Reason is false.
(d) Assertion is false and Reason is true.
(i) Assertion (A): Water or chemicals present in water react with rocks and cause changes in chemical composition of rocks.
Reason (R): Weathering of rocks leads to the formation of soil.
(ii) Assertion (A): Some changes occurring over the years due to human activity can have short-term environmental impact.
Reason (R): Rusting of iron is a slow process.
Fill in the blanks
(i) Insoluble calcium carbonate is _____ in colour. (Red/White)
(ii) Grinding of wheat grains into flour is an example of _____ physical change. (Reversible / Irreversible)
(iii) Iron tawa on exposure to air gets corroded due to _____ of iron. (Rusting/Combustion)
(iv) Fire flies emit light in dark due to _____ (Bioluminescence /Luminescence)
(v) _____ substance on burning in air produces magnesium oxide along with heat and light. (Magnesium/ Aluminium)
True or False
State whether True or False answer with reason
(i) Oxygen gas is used to extinguish fire.
(ii) Bursting of crackers is an example of physical change.
(iii) Bubbles of carbon dioxide are produced when vinegar is added in water.
(iv) Reddish-brown coloured flaky coating on the surface of Iron is called rust.
(v) Breaking of glass into pieces is an example of chemical change.
Match the following:
Question 1.
Match the following items given in Column A with that in Column B:
| Column A | Column B |
| (a) Stretching of rubber band | (i) Chemical change |
| (b) Iron + Air + Water | (ii) Reversible change |
| (c) Colour change in Chameleons | (iii) Iron oxide |
| (d) Burning of LPG in kitchen | (iv) Physical change |