Long-answer questions
1. What is crystallisation? How can you obtain sugar
crystals? Explain.
2. What is rusting? What are the conditions for
rusting? How can rusting be prevented?
3. Explain with examples three types of chemical
changes. Give an example for each.
4. Differentiate between physical and chemical
changes with the help of examples.
Answers
Explanation:
1. it is the process of dehydration of a liquid to give solid it is obtained by heating
Answer : i)
Crystallization is a process that separates a pure solid in the form of its crystals from a solution. We can get crystals of sugar from its solution by evaporation, which can decompose solids on heating.... 1) Some solids decompose or some ,,like sugar , may get charred on heating to dryness..
Answer ii)Process in which brownish red flusky substance stick to iron when it reacts with moist air.
Condition of rusting :
The presence of water and oxygen is essential for the rusting of iron. Impurities in the iron, the presence of water vapor, acids, salts and carbon dioxide hastens rusting. Pure iron does not rust in dry and carbon dioxide free air.
Prevention for rusting :)
i)Paint It. Paint the bare metal with any durable acrylic paint. ...
ii) Keep Moisture at Bay. Avoid contact with water or moisture. ...
iii)Coat It With Oil. Use of oil or grease significantly reduces the chances of developing rust in iron. ...
iv)Other Considerations. Use stainless steel wherever and whenever possible. ...
v) Bacteria Warning.
Answer 4) A chemical change results from a chemical reaction, while a physical change is when matter changes forms but not chemical identity. Examples of chemical changes are burning, cooking, rusting, and rotting. Examples of physical changes are boiling, melting, freezing, and shredding.
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