II Short Answer Type Questions
- How is the melting of ice is a physical change?
Answer. Melting ice is a physical change because it alters state from solid to liquid without changing its chemical composition.
- If you tear a sheet of a paper into small bits, can you get the sheet again? What kind of changes is this and why?
Answer. No, you cannot get the sheet again. This is a physical change because the paper’s composition remains unchanged.
3.How would you detect the presence of carbon dioxide produced during the reaction of vinegar with baking soda?
Answer. Detect carbon dioxide by bubbling the gas through limewater; it turns milky, indicating the presence of CO₂.
4. How would you show that rusting of iron is a chemical change?
Answer. Rusting of iron is a chemical change because it forms a new substance, iron oxide, with different properties.
- Name five chemical changes that takes place inside the body of living beings.
Answer. Digestion, respiration, protein synthesis, cellular respiration, and photosynthesis (in plants) are chemical changes in living beings’ bodies.
III. Long answer type questions
- What are the characteristics of a physical change?
Answer. A physical change alters the form or appearance of a substance without changing its chemical composition. Characteristics include reversibility, no new substance formation, and changes in state, shape, or size. Examples are melting, freezing, tearing, and dissolving.
2. Mention some ways to prevent rusting.
Answer. To prevent rusting, apply paint or a protective coating to metal surfaces, use rust-resistant alloys like stainless steel, and keep metals dry. Galvanization, which coats metals with zinc, and using oil or grease to create a moisture barrier are also effective methods.
3. How does chemical change differ from physical change?
Answer. A chemical change alters the substance’s chemical composition, forming new substances with different properties, and is usually irreversible. A physical change affects only the form or appearance without changing the substance’s chemical identity, and is typically reversible. Examples include burning for chemical and melting for physical changes.
4. What is the importance of chemical changes for living beings?
Answer. Chemical changes are crucial for living beings as they drive essential processes like digestion, respiration, and photosynthesis. These changes enable the conversion of food into energy, the breakdown of waste, and the synthesis of vital molecules, ensuring the survival and proper functioning of organisms.
5. Name the method used to obtain pure crystals of a substance Describe one of its uses.
Answer. The method to obtain pure crystals of a substance is called crystallization. This process is used in many industries, for example, to purify table sugar! Pure sugar crystals form out of the solution by dissolving sugar in water and then carefully evaporating some of the water.
6. When a nail is dipped in a copper sulphate solution. The color of the solution is changed and the nail is covered with a brown layer. Why? Explain this reaction in terms of chemical change.
Answer. It’s a displacement reaction. The iron nail (more reactive) steals the copper from the blue copper sulphate solution. The copper forms a brownish layer on the nail, and the solution turns greenish due to iron sulfate being formed.