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NCERT Solutions Class 7 Science Chapter 5 - Physical And Chemical Changes
Chapter 5 of class 7, Physical and Chemical Changes, covers physical changes, chemical changes, and the rusting of iron. These are the fundamental ideas that students must comprehend in order to perform well on the test.
These solutions contain step-by-step solutions for all NCERT problems, which can help students understand the fundamental concepts easily. For detailed solutions and exercises, refer to the NCERT Solutions for Class 7 Science chapter 5 physical and chemical changes PDF link below. ALLEN's expert teachers created these solutions to improve students' understanding and help them score well on tests by reviewing and practising them.
1.0Download NCERT Solutions Class 7 Science Chapter 5 : Free PDFe
This article provides solutions for Class 7 Physical and Chemical Changes in accordance with NCERT guidelines. Students who practice these solutions gain a better understanding of Chemistry and become more capable of solving problems, which eventually helps them score higher on tests. Students can use the link below to download the NCERT Class 7 Science Chapter 9 PDF Solutions.
2.0NCERT Solutions Class 7 Science Chapter 5 Physical And Chemical Changes: Overview
What are the NCERT solutions, and are they helpful for you? The NCERT Solutions are notes with problems related to the NCERT textbook, and their detailed answers have been given. In chapter 5 of class 7 science, students will face problems related to physical and chemical changes and the rusting of iron. To strengthen their understanding, ALLEN expert teachers have created NCERT solutions that provide a complete step-by-step way to solve all types of questions, whether it is very short answer type, long answer type, or multiple choice.
Subtopics Under Chapter 5 Physical And Chemical Changes
Below are the topics covered in the NCERT solutions for Class 7 Science Chapter 5. These are based on the latest NCERT Class 7 curriculum.
- Physical Changes
- Chemical Change
- Rusting of Iron
3.0NCERT Questions with Solutions for Class 7 Science Chapter 5 - Detailed Solutions
- Classify the changes involved in the following processes as physical or chemical changes: (a) Photosynthesis (b) Dissolving sugar in water (c) Burning of coal (d) Melting of wax (e)Beating aluminium to make aluminium foil (f) Digestion of food Ans. (a) Photosynthesis Chemical change (b) Dissolving sugar in water Physical change (c) Burning of coal Chemical change (d) Melting of wax Physical change (e) Beating aluminium to make aluminium foil Physical change (f) Digestion of food Chemical change
- State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook. (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) Ans. (a) False Cutting a log of wood into pieces is a physical change. (b) False Formation of manure from leaves is a chemical change. (c) True (d) False Iron and rust are different substances. Rust is iron oxide (e) True
- 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. Ans. (a) When carbon dioxide is passed through limewater, 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 galvanisation 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.
- When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain. Ans. When baking soda (Sodium hydrogen carbonate) is mixed with lemon juice (citric acid), bubbles are formed. The bubbles are formed due to the evolution of carbon dioxide gas. This is a chemical change. In this change, citric acid contained in lemon juice reacts with sodium hydrogen carbonate which results in the evolution of carbon dioxide gas. Lemon juice + Baking soda Carbon dioxide + Other substances
- When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place. Ans. When a candle burns, both physical and chemical changes take place. Physical change Melting of wax Chemical change Burning of wax Eating of food is another example where both physical and chemical changes occur simultaneously. Physical change Breaking down of larger food particles into smaller particles Chemical change Digestion of food
- How would you show that setting of curd is a chemical change? Ans. Once the curd is formed, milk cannot be re-obtained from it. Also, both milk and curd have different properties. Since these are the properties of a chemical change, setting of curd is a chemical change.
- Explain why burning of wood and cutting it into small piece are considered as two different types of changes. Ans. When we burn wood, a new substance, coal is formed. Therefore, it is a chemical change. However, when we cut wood, only the shape and size of the wood are changed. No new substance is formed. Therefore, it is a physical change.
- Describe how crystals of copper sulphate are prepared. Ans. Crystals of copper sulphate are prepared by the method of crystallisation. The process is as follows. A cup full of water is taken in a beaker. Few drops of dilute sulphuric acid are added to this. The water is then heated and when it starts boiling, copper sulphate powder is added with stirring. Copper sulphate powder should be added in the solution till it becomes saturated. It is then filtered into a china dish and allowed to cool. The solution should be kept undisturbed. Slowly, the crystals of copper sulphate separate out.
- Explain how painting of an iron gate prevents it from rusting. Ans. Rusting is aided by both moisture (water) and air (oxygen). By painting an iron gate, we prevent its contact from the air and moisture present in the atmosphere. Hence, rusting is prevented.
- Explain why rusting of iron objects is faster in coastal areas than in deserts. Ans. Both air and moisture are required for rusting to take place. In coastal areas, the quantity of moisture present in air is more than that in deserts. In desert areas, the amount of moisture in air is even lower. Therefore, rusting of iron objects is faster in coastal areas than in deserts.
- The gas we use in the kitchen is called liquefied 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). 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. Ans. (ii) Process - B is a chemical change.
- Anaerobic bacteria digest animal waste and produce biogas (Change-A). The biogas is then burnt as fuel (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. Ans. (iii) Both processes A and B are chemical changes.
Exercise-01
Multiple choice questions
- Which among the following is not a physical change? (1) Melting of solids to liquids (2) Vaporisation of liquids to gases (3) Liquefaction of gases to liquids (4) Decay of matter
- An example of a chemical change is . (1) formation of clouds (2) glowing of an electric light (3) dropping sodium into water (4) dissolving of salt in water
- Which among the following is not a chemical change? (1) Melting of ice (2) Carbon cycle (3) Dehydration of substances (4) Fermentation of substances
- Which of these will cause a chemical change to occur? (1) Grinding of wheat into flour (2) Lighting of a gas stove (3) Evaporation of water from a lake (4) Ringing of an electric bell
- Chemical changes are . (1) temporary, reversible and a new substance is produced (2) always accompanied by exchange of light (3) permanent, irreversible and a new substance is produced (4) never accompanied by exchange of light and heat energy
- Which of the following is a physical change? (1) Solubility in water (2) Combustibility (3) Aerial oxidation (4) Reaction with water
- Physical changes are . (1) temporary (2) permanent (3) irreversible (4) endothermic
- Which of the following is a physical change? (1) Rusting of iron (2) Combustion of magnesium ribbon (3) Burning of candle (4) Melting of wax
- A chemical change may involve (1) change in colour only (2) change in temperature only (3) evolution of gas only (4) any or all of the above
- Which of the following are true when milk changes into curd? (i) Its state is changed from liquid to semi solid. (ii) It changes colour. (iii) It changes taste. (iv) The change cannot be reversed. Choose the correct option from below: (1) (i) and (ii) are correct. (2) (ii) and (iii) are correct. (3) (i), (iii) and (iv) are correct. (4) (i) to (iv) are correct.
- What does a chemical change involve? (1) Formation of substance with different states (2) Formation of substance with different chemical properties (3) Formation of substance with different size (4) Formation of substance with different shapes
- Which of the following is an irreversible physical change? (1) Freezing of water (2) Melting of ice (3) Burning paper (4) Cutting of wood in small pieces
- Rusting of iron is (1) an irreversible chemical change (2) a reversible chemical change (3) an irreversible physical change (4) a reversible physical change
- The change of state of a substance from solid to liquid and liquid to gas is (1) a physical change (2) a chemical change (3) combination of a physical and chemical change (4) sometimes physical change and sometimes chemical changes
- Galvanisation of a process in which (1) iron is coated on zinc metal. (2) zinc and iron are mixed in molten state. (3) zinc is coated as a layer on iron. (4) carbon is mixed with iron and heated.
- Dissolve some common salt in water and leave the solution in an open and sunny place for a day. What do you observe? (1) The whole of the solution evaporates (2) Water evaporates leaving behind salt (3) Salt evaporates leaving behind water (4) No change of any form in the salt solution
- What kind of change is involved when a sheet of paper is shredded? (1) An irreversible chemical change (2) A reversible chemical change (3) A irreversible physical change (4) A reversible physical change
- Which of the following is not a physical change? (1) Breaking of a glass tumbler (2) Melting of butter (3) Dissolving of sugar in water (4) Ripening of a fruit
- When an iron spade is left lying in a moist atmosphere it (1) develops brown powdery layer of iron oxide (2) develops green layer of iron oxide (3) develops brown layer of oxygen (4) does not undergo any change
- Which of the following is a chemical change? (1) Cutting of a cloth (2) Ironing of a cloth (3) Drying of a cloth (4) Burning of a cloth
Classify the following as physical or chemical change
- Dissolving zinc metal in hydrochloric acid.
- Making cheese from milk.
- Making wine from grapes.
- Obtaining milk powder from milk.
- Burning of paper.
Fill in the blanks
- ______ like boiling do not make new substances and are easily reversed by condensation.
- In ______ change no new substance is formed.
- A foul-smelling spoiled food is a _______ change.
- Properties such as shape, size, colour and state of a substance are called _________ properties.
- Turning of lime water to milky is a standard test of _______ gas.
- A chemical change is also called a _________
Match the column
Crossword puzzle
Across
- In a chemical reaction when reactants react they convert into .
- Rusting is a change.
- Magnesium ribbon burns with light.
- Copper sulphate crystals are in colour.
Down
- A physical change generally in nature.
- Burning of candle is a change.
- Carbon dioxide turns lime water .
Answer Key
Multiple choice questions
Classify the following as physical or chemical change.
- Chemical
- Chemical
- Chemical
- Physical
- Chemical
Fill in the blanks.
- physical change
- physical
- chemical
- physical
- chemical reaction
- chemical
- chemical
- air and water
- Acetic Acid
True or False
- True
- True
- True
- False
- False
- False
- False
- True
- True
- False
Match the column
- (1) ; ; (3) ; (5) ; (6)
Crossword puzzle
Exercise-02
Very short answer type questions
- In which changes do substance undergo chemical transformation - physical or chemical?
- What method will you use to get a pure solid if it has dissolved impurities present in it?
- Which one is a chemical change rusting of iron or melting of iron?
- Write word equations for the following: (i) Carbon reacting with oxygen to form carbon dioxide. (ii) Magnesium burning in oxygen to form magnesium oxide.
- Define crystallisation.
- What happens when a iron nail is dipped in a copper sulphate solution?
- Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings.
- What kind of change is shown by tearing of paper?
- Name the gas which turns lime water milky.
- What colour of flame is observed when magnesium ribbon burnt in air.
- Write the colour of copper sulphate solution obtained when iron nails are dipped in it?
- How can you say that ripening of a fruit is a chemical change?
- Is souring of milk a physical change or a chemical change? Why?
- Complete the following reaction
- Name the process by which common salt is obtained from sea water. Short answer type questions
- Why are water pipes galvanized?
- How can the crystals of sodium chloride be prepared from table salt?
- When water is frozen, it forms ice that has different properties. Why then do we say that freezing is a physical change?
- What do you meant by skeletal equation?
- Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
- Explain why burning of wood and cutting it into small pieces are considered as two different types of changes?
- Why a chemical change cannot be normally reversed?
- Is cloud formation a physical change or a chemical change? Explain.
- What is galvanisation?
- How would you show that setting of curd is a chemical change?
Long answer type questions
- Discuss the methods by which rusting of iron can be prevented.
- Which gas is given off when dilute hydrochloric acid is added to calcium carbonate? How will you test the gas? Write the chemical equations for both reactions.
- Describe how crystals of copper sulphate are prepared.
- When a candle burns, both physical and chemical changes take place. Identify these changes. Give another example of a familiar process in which both the chemical and physical changes take place.
- When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a gas. What type of change is it? Explain.
Exercise-01 Solutions
Multiple choice questions
- Option (4) Decay of matter is the only chemical change.
- Option (3) When sodium is dropped into water, it forms NaOH with evolution of gas. Formation of substance is chemical change.
- Option (1) Melting of ice is a physical change.
- Option (2) Gas will burn in the presence of air, to form different products like gas and water vapours.
- Option (3) A new substance with different properties is formed during chemical change, which may not be reverse by simpler methods. It is a permanent change.
- Option (1) No new substance is formed when a substance dissolved in water.
- Option (1) Physical changes may be reversed easily, so they are temporary changes.
- Option (4) Melting of wax is a physical change as no new substance is formed.
- Option (4) Chemical change accompanied by some physical change also.
- Option (3) Curdling of milk is a chemical change so new substance is formed with some physical change also.
- Option (2) In a chemical change, a new substance is formed which has different chemical properties from the constituents.
- Option (4) Cutting of a wood is a physical but irreversible change.
- Option (1) Rusting of iron is a chemical change and it cannot be reversed.
- Option (1) When a solid melts to form a liquid and a liquid boils to form a gas only a physical change takes place.
- Option (3) Galvanisation is a process in which iron is coated with a layer of zinc.
- Option (2) Salt solution on evaporation leaves behind salt while water is evaporated.
- Option (3) An irreversible physical change takes place when a sheet of paper is shredded.
- Option (4) Ripening of a fruit is a chemical change.
- Option (1) When an iron spade is left in the moist atmosphere it reacts with oxygen and water to form a brown powder of iron oxide called rust.
- Option (4) Burning of a cloth is a chemical change.
True or False
- True Heat, light or any other radiation (ultraviolet, for example) may be given off or absorbed, during chemical change.
- True Only the physical state or some of the physical properties of the substances are changed, during a physical change.
- True Chemical change cannot be reversed.
- False Making cloth from yarn, is a physical change; because there is no change in chemical composition only physical properties are change.
- False It is a physical change because no new substance is formed.
- False Its a chemical change, rust is a completely different substance from iron.
- False Cutting a log of wood is a physical change because only shape and size changes no new substance is formed.
- True As a physical change, wax turns into molten wax and as chemical change it burns to produce carbon dioxide and water vapour also.
- True Condensation is physical change because only state of water gets change no new substance is formed.
- False Formation of manure from leaves is a decomposition reaction so it is a chemical change.
Exercise-02 Solutions
Very short answer type questions
- In chemical changes, substances undergo chemical transformation.
- Crystallisation method can be used to get a pure solid if it has dissolved impurities in it.
- Rusting of iron is an example of chemical change.
- (i) (ii)
- The process of cooling a hot, concentrated solution of a substance to obtain crystals is called crystallisation.
- When an iron nail is dipped in solution iron can displace copper from its solution. The iron nail gets coated with a brown layer of copper and the colour of the blue copper sulphate solution changes to pale green.
- Melting of ice is a such change in which change of state is taken place.
- Tearing of paper is a physical irreversible change.
- Carbon dioxide gas turn lime water milky.
- When magnesium ribbon get burn it gives dazzling white light.
- Colour of copper sulphate solution changes to green due to displacement reaction.
- Ripening of fruit is a chemical change as its composition is change due to chemical reaction.
- Souring of milk is a chemical change as new substance is formed due to chemical reaction.
- Common salt obtain from sea water by the process called evaporation and crystallization.
Short answer type questions
- Water pipes are made up of iron and galvanised to prevent them from rusting. When a piece of iron is left in moist air for some time, a reddish brown solid is deposited over it. Which is called rust and forming of rust is called rusting so to prevent iron water pipes from rusting, we electroplate the surface of metal by zinc, which is known as galvanisation.
- By using crystallisation method, we can prepare the crystals of sodium chloride from table salt. According to crystallisation method first we'll prepare a hot concentrated solution of table salt in water then we'll cool it and remain it undisturbed. After some days we'll get crystals of sodium chloride.
- When water is frozen, it forms ice that has different properties but still we say its a physical change because the identity of water is still same, this change is temporary means if we start melting ice it will come to its original state which is liquid.
- A skeletal equation is an unbalanced chemical reaction consists of unequal number of atoms of elements of reactants and products.
- When grapes are attached to the plant, they are living and their defence mechanism i.e immune system prevents their fermentation. The micro bacterias that ferment grapes can grow easily on the plucked grapes and under anaerobic condition(absence of ) fermentation results. This is a chemical change.
- When we burn wood, it turns into ashes which is a new substance and the process is irreversible one, hence it is a chemical change. While cutting the wood into small pieces no new substance is formed. It is a physical change.
- In chemical change new products are formed which have different chemical composition hence it cannot be reversed back. For example - Paper burns to form ash and ash has different chemical composition and it cannot be reversed back to paper.
- The formation of clouds is a physical change because there is a phase transformation cycle of natural water from liquid to gas and then, gas to liquid.
- Galvanization or galvanizing is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are coated by submerging them in a bath of hot, molten zinc
- The curd is formed from milk. Both curd and milk have different properties. So, there is a formation of a new substance with different properties and once the curd is formed, it cannot be reversed back to milk. Therefore, the setting of curd is a chemical change.
Long answer type questions
- Prevention of rusting As stated earlier rusting will take place only, if iron is simultaneously acted upon by water and oxygen (from air). So, if we prevent the iron articles to come in contact with air or water or both, the rusting will stop. Rusting of iron surface exposed to the air is prevented by application of protective coatings on iron. (i) By painting : The corrosion of a metal can be prevented simply by painting the metal surface by grease or varnish that forms a protective layer on the surface of the metal which protect the metal from moisture and air. (ii) Electroplating : It is a very common and effective method to prevent corrosion. The surface of metal is coated with chromium, nickel or aluminium etc. by electrolysis also called electroplating. They are quite resistant to the attack by both air and water and prevent corrosion. If the surface of metal is electroplated by zinc, it is known as galvanisation and in case tin metal is used, then the process is called tinning.
- Carbon dioxide gas is given off when dilute hydrochloric acid is added to calcium carbonate. Equation:- To test carbon dioxide gas, we will pass carbon dioxide in lime water which is a solution of calcium hydroxide. When carbon dioxide is passed through it, a solid precipitate of calcium carbonate is formed and lime water turned 'milky' or 'Cloudy'.
- The crystals of copper sulphate are obtained by the process of Crystallization. In this process, a few drops of dilute sulphuric acid are added to water. Then water is boiled and copper sulphate powder is added to the boiling water with stirring. The powder is added until the solution becomes saturated.
- 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. Digestion of food is another example where both physical and chemical changes occur simultaneously.
- When a baking soda is mixed with the lemon juice then Carbon dioxide gas is released in the form of bubbles. As the chemical composition of the substance is getting changed and as the new product is formed by the mixing. Therefore, it is a Chemical change.
4.0Chapter 5 Physical And Chemical Changes Class 7 Solutions of NCERT: Benefits
- The solutions break down difficult topics, making understanding the difference between physical and chemical changes easier, improving overall learning.
- By practising with step-by-step solutions, students improve their ability to solve different types of questions, which is essential for mastering scientific topics.
- The exercises in the solutions are similar to the questions on the exam. They help students prepare for their assessments with confidence.
- Available in both English and Hindi, these solutions ensure students can learn without language barriers.
- NCERT Solutions for Class 7 Science Chapter 5 helps students understand the subject, improve their problem-solving skills, and prepare for exams.
- NCERT Solutions helps students understand important concepts such as physical and chemical changes