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.
5. 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.
6. How would you show that setting of curd is a chemical change?
7. Explain why burning of wood and cutting it into small pieces are
considered as two different types of changes.
8. Describe how crystals of copper sulphate are prepared.
9. Explain how painting of an iron gate prevents it from rusting.
10. Explain why rusting of iron objects is faster in coastal areas than in
deserts.
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.
Answers
Answer:
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Answer:
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Explanation:
4.Solution: When baking soda is mixed with lemon juice, bubbles are formed with the evolution of a carbon dioxide gas. This is a chemical change.
5.Since, it again turns into solid wax on cooling. The change is reversible. Chemical changes in burning candle The wax near to flame burns and gives new substances like carbon dioxide, carbon soot, water vapours, heat and light. Cooking of food, boiling of eggs are examples of both physical and chemical changes.
6.Answer: Setting of a curd is a chemical change because curd cannot be converted into milk again. Moreover, a new substance, curd is formed which is completely different in taste and properties from the milk.
7.Question: Explain why burning of wood and cutting it into small pieces are considered as two different types of changes. Answer: When we burn wood, it turns into ashes which is a new substance and process is irreversible one, hence is a chemical change.
8.Crystallization is the process by which we can obtain crystals of copper sulphate. In this process, a few drops of dilute sulphuric acid is added to water. The water is then boiled & as it starts boiling, copper sulphate powder is added with stirring. The powder must be added on till the solution becomes saturated.Jun 24, 2019
9Answer: We know that for rusting, the presence of both oxygen and water (water vapour) is essential. Thus, in coastal areas, the air contains high moisture which means more humid environment and rusting becomes faster.
10.Answer: We know that for rusting, the presence of both oxygen and water (water vapour) is essential. Thus, in coastal areas, the air contains high moisture which means more humid environment and rusting becomes faster.
11.Liquified petroleum gas is filled in the cylinder in the form of a liquid. When these liquids come out of the cylinder in the form of vapours, physical change takes place. When these vapours are mixed with air and burn, chemical change takes place.
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