NCERT Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes
NCERT solutions for class 7 science chapter 6 physical and chemical changes : Many changes happen in this world as time passes. These changes are of different types. Class 7 NCERT science explains some physical and chemical changes around us. The solutions of NCERT class 7 science chapter 6 physical and chemical changes help in familiarising with the concepts studied in the chapter. There are 12 questions in the exercise. All these questions are discussed in the CBSE NCERT solutions for class 7 science chapter 6 physical and chemical changes. The changes in shape, size colour or state are physical changes. When one or more new substances are formed during a change then the changes are chemical changes. To understand both physical and chemical changes there are different interesting activities mentioned in the NCERT class 7 science chapter 6. Along with these activities, practicing the NCERT solutions for class 7 science chapter 6 physical and chemical changes can make your learning better. You can get NCERT solutions from class 6 to 12 for science and maths by clicking on the above link.
Topics of NCERT class 7 science chapter 6 physical and chemical changes:
6.1 Physical Changes
6.2 Chemical Change
6.3 Rusting of Iron
6.4 Crystallisation
NCERT solutions for class 7 science chapter 6 physical and chemical changes
1. Classify the changes involved in the following processes as physical or chemical changes:
(a) Photosynthesis
Answer:
(a) Photosynthesis is a chemical change.
1. Classify the changes involved in the following processes as physical or chemical changes:
(b) Dissolving sugar in water
Answer:
(b) Dissolving sugar in water is a physical change.
1. Classify the changes involved in the following processes as physical or chemical changes:
(c) Burning of coal
Answer:
(c) Burning of coal is a chemical change.
1. Classify the changes involved in the following processes as physical or chemical changes:
(d) Melting of wax
Answer:
(d) Melting of wax is a physical change.
1. Classify the changes involved in the following processes as physical or chemical changes:
(e) Beating aluminium to make aluminium foil
Answer:
(e) Beating aluminium to make aluminium foil is a physical change.
1. Classify the changes involved in the following processes as physical or chemical changes:
Answer:
Digestion of food is a chemical change.
During digestion, enzymes in the stomach and intestines break down food molecules into simpler molecules.
(a) Cutting a log of wood into pieces is a chemical change. (True/False)
(b) Formation of manure from leaves is a physical change. (True/False)
(c) Iron pipes coated with zinc do not get rusted easily. (True/False)
(d) Iron and rust are the same substances. (True/False)
(e) Condensation of steam is not a chemical change. (True/False)
Answer:
(a) False because cutting a log of wood into pieces is a physical change.
(b) False because the formation of manure from leaves is a chemical change.
(c) True.
(d) False because Iron and rust are different substances.
(e) True
3. Fill in the blanks in the following statements:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of _________.
(b) The chemical name of baking soda is _________.
(c) Two methods by which rusting of iron can be prevented are _________ and _________.
(d) Changes in which only _________ properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called _________ changes.
Answer:
(a) When carbon dioxide is passed through lime water, it turns milky due to the formation of calcium carbonate.
(b) The chemical name of baking soda is sodium hydrogen carbonate.
(c) Two methods by which rusting of iron can be prevented are galvanization and painting.
(d) Changes in which only physical properties of a substance change are called physical changes.
(e) Changes in which new substances are formed are called chemical changes.
4. When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Answer:
When baking soda is mixed with lemon juice then it is a chemical change, bubbles are formed with the evolution of a carbon dioxide gas.
Answer:
When a candle burns, both physical and chemical changes take place. On heating, candle wax gets melted is a physical change since it again turns into wax on cooling.
The wax gives carbon dioxide, heat, light, water vapour and carbon soot on heating with states chemical change.
Another example is the lightening of the bulb using a dry cell.
6. How would you show that setting of curd is a chemical change?
Answer:
The setting of curd is a chemical change because the new substance(curd) formed from milk differs in taste and it cannot be converted into milk again i.e. it is irreversible.
Answer:
The burning of wood is a chemical change because wood after burning gives carbon dioxide, ash, heat, water vapour also it is an irreversible process.
Whereas cutting wood into small pieces is a physical change because the original composition of wood remains the same and no new substance is formed.
8. Describe how crystals of copper sulphate are prepared.
Answer:
The crystals of copper sulphate are prepared as follows:
1. A cup of water is taken in a beaker.
2. Add some drops of dilute sulphuric acid in it.
3. Heat it and when it starts boiling add copper sulphate powder slowly with continuous stirring.
4. The copper sulphate powder is added till the saturation level.
5. Filter the solution and cool it.
6. Leave it undisturbed and we will observe copper sulphate crystals after some hours.
9. Explain how painting of an iron gate prevents it from rusting.
Answer:
Painting of an iron gate prevents direct contact of iron with water and air(oxygen) which are required for rusting.
No exposure of water and oxygen with iron prevents iron from rusting.
10. Explain why rusting of iron objects is faster in coastal areas than in deserts.
Answer:
Rusting occurs with direct contact of iron with water and oxygen.
In coastal areas,the moisture content is high in the air which states rusting of iron objects is faster in coastal areas because in deserts moisture in the air is absent.
11. The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder, it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). This is a chemical change.
Thus, option (ii) is correct.
(i) Process – A is a chemical change.
(ii) Process – B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
Anaerobic bacteria digest animal waste and produce biogas (Change – A). The biogas is then burnt as fuel (Change – B).
Both process A and B are a chemical change.
Thus, option (iii) is correct.
Chapterwise NCERT solutions of class 7 science
NCERT Solutions for Class 7 Subject Wise
Important terms to be remembered :
The main terms to be memorised after going through the chapter and also NCERT solutions for class 7 science chapter 6 physical and chemical changes are listed below.
- Crystallisation: The process of forming large crystals of pure substances are known as crystallisation.
- Rusting of iron: If iron is kept in moist air a brownish film is formed on the iron. The brownish substance is called rust and the process is called rusting.
- Galvanisation: In the NCERT class 7 book the given definition is- Galvanisation is the process of depositing a layer of zinc on iron. Galvanisation prevents iron from rusting.
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