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Physical and Chemical Changes Class 7 Extra Questions Science Chapter 6
Physical and Chemical Changes in class 7 Science chapter 6 is a fundamental concept that distinguishes between different types of changes in matter. This chapter, also known as Chapter 6 in the CBSE syllabus, explores the distinctions between physical changes, which alter the physical properties of substances without forming new ones, and chemical changes, which result in the formation of new substances through chemical reactions.
Extra questions for Class 7 Science Chapter 6 provide students with additional practice to reinforce their understanding of physical and chemical changes. These questions are designed to challenge students’ comprehension and analytical skills, encouraging them to think critically about the concepts taught in the chapter. By solving these extra questions, students can enhance their grasp of the subject and better prepare for their examinations.
Class 7 Chemistry Chapter 6 Physical and Chemical Changes Important Questions PDF Download
For students aiming to excel in their exams, having access to a PDF containing important questions for Chapter 6 can be a valuable resource. This PDF typically includes a curated list of questions that cover key concepts and are likely to appear in examinations. These questions not only help in reinforcing the understanding of the topic but also provide a good practice for exam preparation.
Science Class 7 Chapter 6 Physical and Chemical Changes Extra Questions and Answers
Physical and Chemical Changes Class 7 Science Extra Questions Short Answer Type Questions – (SAQs)
Question 1: What kind of change is shown by tearing of paper?
Answer: Tearing of paper is a physical change.
Question 2: Melting of wax is a change where a solid changes to liquid state. Give one more such change which you observe in your surroundings?
Answer: Melting of ice to water is another change where solid changes to liquid state.
Question 3: Name the gas which turns lime water milky.
Answer: Carbon dioxide gas turns lime water milky.
Question 4: Give an example of a physical change that occurs by the action of heat.
Answer: Melting of ice to form water is a physical change that occurs by the action of heat.
Question 5: Write the color of copper sulfate solution obtained when iron nails are dipped in it.
Answer: The color of the solution changes to green when iron nails are dipped in copper sulfate solution.
Question 6: What color of flame is observed when magnesium ribbon is burnt in the air?
Answer: A brilliant white flame is observed when magnesium ribbon is burnt in the air.
Question 7: How can you say that ripening of a fruit is a chemical change?
Answer: Ripening of a fruit is a chemical change because it involves the transformation of substances into new products with different properties.
Question 8: Is souring of milk a physical change or a chemical change? Why?
Answer: Souring of milk is a chemical change because it involves the formation of new substances like lactic acid.
Question 9: What is the nature of magnesium oxide solution?
Answer: Magnesium oxide solution is basic in nature.
Question 10: Name the process by which common salt is obtained from seawater.
Answer: Common salt is obtained from seawater by the process of evaporation.
Question 11: Name the metal which is used for galvanizing iron.
Answer: Zinc metal is used for galvanizing iron.
Question 12: Name the metals that are mixed (alloyed) with iron to make stainless steel.
Answer: Chromium and nickel are mixed with iron to make stainless steel.
Question 13: Suggest two methods to prevent rusting.
Answer: Two methods to prevent rusting are painting the iron articles and greasing or oiling the iron articles.
Question 14: Why should we eat freshly cut apples?
Answer: We should eat freshly cut apples because once cut, they start to oxidize, which reduces their nutritional value and freshness.
Question 15: Classify the following processes into physical or chemical changes.
(a) Beating of aluminum metal to make aluminum foil
(b) Digestion of food
(c) Cutting of a log of wood into pieces
(d) Burning of crackers
Answer:
(a) Physical change
(b) Chemical change
(c) Physical change
(d) Chemical change
Question 16: Is cloud formation a physical change or chemical change? Explain.
Answer: Cloud formation is a physical change as it involves the condensation of water vapor into water droplets without any new substances being formed.
Question 17: Write the differences between physical and chemical changes.
Answer: In physical changes, no new substances are formed, and the changes are usually reversible. In chemical changes, new substances are formed, and the changes are usually irreversible.
Question 18: In addition to the formation of new products, what changes do the chemical changes accompany?
Answer: Chemical changes may be accompanied by the evolution or absorption of heat, light, or sound, a change in smell, a color change, and the formation of a gas.
Question 19: Magnesium ribbon burns in air and changes to a white substance, i.e., magnesium oxide. When magnesium oxide dissolves in water, what type of change takes place? Give a reason in support of your answer. Express the change in the form of an equation.
Answer: It is a chemical change. Magnesium oxide reacts with water to form magnesium hydroxide. Equation: MgO + H2O → Mg(OH)2
Question 20: What is stainless steel? How is stainless steel made? State an important property of stainless steel.
Answer: Stainless steel is an alloy made by mixing iron with carbon, chromium, and nickel. An important property of stainless steel is that it does not rust.
Question 21: Plants prepare their food by a process called photosynthesis. Can we call photosynthesis a chemical change? Explain.
Answer: Yes, photosynthesis is a chemical change because it involves the conversion of carbon dioxide and water into glucose and oxygen using sunlight.
Question 22: The process of digestion is a chemical change. Explain why.
Answer: Digestion is a chemical change because it involves the breakdown of complex food substances into simpler absorbable forms, resulting in the formation of new substances.
Question 23: How does the ozone layer act as a protective shield?
Answer: The ozone layer acts as a protective shield by absorbing harmful ultraviolet radiations from the sun, thus protecting life on Earth from their damaging effects.
Question 24: Explosion of a cracker is a chemical change. Explain.
Answer: The explosion of a cracker is a chemical change because it involves the rapid reaction of chemicals within the cracker, producing heat, light, sound, and new substances.
Question 25: Why can’t a chemical change be normally reversed?
Answer: A chemical change can’t be normally reversed because it results in the formation of new substances with different properties, making it difficult to revert to the original substances.
Question 26: Describe two changes that are harmful. Explain why you consider them harmful. How can you prevent them?
Answer: Two harmful changes are rusting of iron, which weakens metal structures, and spoilage of food, which can lead to health issues. Rusting can be prevented by painting or galvanizing, while spoilage can be prevented by proper storage and preservation.
Question 27: What happens when an iron blade of a knife is dipped in a copper sulfate solution? What kind of change takes place?
Answer: When an iron blade is dipped in a copper sulfate solution, a chemical change occurs. The iron reacts with the copper sulfate, forming iron sulfate and depositing copper on the blade, changing the solution’s color from blue to green.
Long Answer Type Extra Question for Science Class 7 Chapter 6 Physical and Chemical Changes
Question 1: Explain how the painting of an iron gate prevents it from rusting.
Answer: Painting an iron gate provides a protective barrier that prevents the iron from coming into contact with oxygen and water, which are the two essential elements for rusting. Rusting is an oxidation reaction where iron reacts with oxygen in the presence of water to form iron oxide, commonly known as rust. By painting the gate, we create a layer that isolates the iron from the environmental factors that cause rusting, thereby prolonging the lifespan of the gate.
Question 2: Why is the melting of ice a physical change?
Answer: The melting of ice is a physical change because it involves a change in the physical state of water from solid (ice) to liquid without altering its chemical composition. In this process, the molecules of water rearrange themselves, but the molecular structure remains the same. Additionally, this change is reversible, as the water can be frozen back into ice, further indicating that it is a physical change.
Question 3: What happens when carbon dioxide is passed through lime water?
Answer: When carbon dioxide is passed through lime water, a chemical reaction occurs, resulting in the formation of calcium carbonate, which is a white precipitate. This reaction is used as a test for the presence of carbon dioxide. The equation for the reaction is:
The lime water, which is a solution of calcium hydroxide, turns milky due to the formation of insoluble calcium carbonate.
Question 4: Why is the rusting of iron objects faster in coastal areas than in deserts?
Answer: Rusting of iron is faster in coastal areas than in deserts because coastal areas have higher humidity levels, providing more moisture in the air. Rusting is an oxidation process that requires both oxygen and water (or water vapor) to occur. In coastal areas, the presence of salt in the air can also accelerate the rusting process by increasing the conductivity of water, thereby facilitating the electrochemical reactions involved in rusting. In contrast, deserts have dry air with low humidity, which slows down the rusting process.
Question 5: Why is the stretching of a rubber band a physical change?
Answer: The stretching of a rubber band is a physical change because it involves a change in the shape and size of the rubber band without altering its chemical composition. The molecules in the rubber band are elongated but remain intact, and the change is reversible, as the rubber band returns to its original shape when the stretching force is removed. No new substances are formed during this process, indicating that it is a physical change.
Question 6: Ozone acts as a natural shield against ultraviolet radiation. Explain.
Answer: Ozone, which is a molecule composed of three oxygen atoms (O3), acts as a natural shield in the Earth’s stratosphere, absorbing a significant portion of the harmful ultraviolet (UV) radiation from the sun. This protective layer, known as the ozone layer, prevents most of the UV radiation from reaching the Earth’s surface, where it can cause skin cancer, cataracts, and other health problems in humans, as well as damage to ecosystems. The absorption of UV radiation by ozone molecules leads to their temporary dissociation into an oxygen molecule (O2) and a single oxygen atom (O), which can then recombine to form ozone, thus maintaining the balance of the ozone layer.
Question 7: What happens when a magnesium ribbon is burnt in the air?
Answer: When a magnesium ribbon is burnt in the air, it reacts vigorously with oxygen to produce a bright white light and forms magnesium oxide, a white powdery substance. The reaction is highly exothermic, releasing a significant amount of heat. The chemical equation for this reaction is:
This reaction is an example of a combustion reaction and demonstrates the chemical change of magnesium metal to magnesium oxide.
Question 8: What is rusting?
Answer: Rusting is a common term for the corrosion of iron and its alloys, such as steel. It is a chemical process in which iron reacts with oxygen in the presence of water or moisture to form iron oxide, commonly known as rust. The chemical equation for rusting is:
Rusting leads to the deterioration of the material, causing it to weaken and eventually disintegrate. It is a significant issue in maintaining the integrity of structures and equipment made of iron or its alloys.
Question 9: Why are chemical changes important in our daily lives?
Chemical changes are crucial in our daily lives as they are involved in various processes and products that we use every day. For example, cooking involves chemical changes that transform raw ingredients into edible food. Digestion is another example, where complex food molecules are broken down into simpler substances that our bodies can absorb. Additionally, chemical changes are essential in industrial processes, such as the production of medicines, plastics, fuels, and other materials. They also play a vital role in environmental processes, such as the decomposition of organic matter and the purification of water. Understanding chemical changes allows us to control and optimize these processes for our benefit and the environment’s sustainability.
CBSE Class 7 Science Chapter 6 Physical and Chemical Changes Multiple Choice Questions (MCQs)
Question 1: What type of change is the rusting of iron?
A) Physical change
B) Chemical change
C) Both physical and chemical change
D) None of the above
Answer: B) Chemical change
Question 2: Melting of ice is an example of which type of change?
A) Physical change
B) Chemical change
C) Both physical and chemical change
D) None of the above
Answer: A) Physical change
Question 3: Which of the following is a chemical change?
A) Boiling of water
B) Freezing of water
C) Burning of paper
D) Melting of wax
Answer: C) Burning of paper
Questions 4: What happens when carbon dioxide is passed through lime water?
A) It turns milky
B) It turns pink
C) It turns colorless
D) No change occurs
Answer: A) It turns milky
Question 5: Which of the following is NOT a physical change?
A) Dissolving sugar in water
B) Cutting a paper
C) Cooking of food
D) Stretching a rubber band
Answer: C) Cooking of food
Question 6: The formation of curd from milk is an example of:
A) Physical change
B) Chemical change
C) Both physical and chemical change
D) None of the above
Answer: B) Chemical change
Question 7: Which of the following statements is true about physical changes?
A) They are irreversible
B) They produce new substances
C) They involve changes in the chemical composition
D) They can be reversed
Answer: D) They can be reversed
Question 8: Rusting of iron requires:
A) Only oxygen
B) Only water
C) Both oxygen and water
D) Neither oxygen nor water
Answer: C) Both oxygen and water
Question 9: Which of the following is an example of a chemical change?
A) Dissolving salt in water
B) Tearing a piece of paper
C) Burning of candle
D) Freezing of water
Answer: C) Burning of candle
Question 10: When a magnesium ribbon is burnt in air, it forms:
A) Magnesium chloride
B) Magnesium oxide
C) Magnesium sulphate
D) Magnesium carbonate
Answer: B) Magnesium oxide
FAQs on CBSE Class 7 Science Chapter 6 Physical and Chemical Changes
What is the difference between a physical change and a chemical change?
A physical change is a change in which the form or appearance of a substance changes, but its chemical composition remains the same. Examples include melting of ice, boiling of water, and cutting of paper. A chemical change, on the other hand, results in the formation of one or more new substances with different chemical properties. Examples include rusting of iron, burning of paper, and souring of milk.
Is melting of wax a physical change or a chemical change?
Melting of wax is a physical change. When wax melts, it changes from solid to liquid form, but its chemical composition remains the same. The process is reversible, and no new substances are formed.
Why is rusting considered a chemical change?
Rusting is considered a chemical change because it results in the formation of a new substance, iron oxide, which has different chemical properties from the original iron. The process involves a reaction between iron, oxygen, and water, leading to a change in the chemical composition of the iron.
Can physical changes be reversed?
Yes, most physical changes can be reversed. For example, melted ice can be refrozen to form solid ice again, and water vapor can be condensed back into liquid water. However, some physical changes, like breaking a glass, are not easily reversible.
What happens when carbon dioxide is passed through lime water?
When carbon dioxide is passed through lime water, it reacts with the calcium hydroxide in the lime water to form calcium carbonate, which is a white precipitate. This reaction causes the lime water to turn milky. The chemical equation for this reaction is: CO2(g) + Ca(OH)2(aq) → CaCO3(s) + H2O(l).
Why are chemical changes important?
Chemical changes are important because they are responsible for the formation of new substances with different properties. They play a crucial role in various natural processes and human activities, such as digestion of food, photosynthesis, cooking, and manufacturing of products like medicines, plastics, and metals. Understanding chemical changes is essential for advancements in science, technology, and industry.
