Physical and Chemical Changes

Q1. Fill in the blanks.

                           i.        Cutting a log of wood into pieces is a physical change.

                          ii.        Condensation is a physical change.

                         iii.        When carbon dioxide is passed through lime water, it turns milky due to the formation of Calcium Carbonate.

                         iv.        Two methods by which rusting of iron can be prevented are painting or greasing and galvanisation.

                         v.        Changes in which only physical properties of a substance change are called physical changes.

                       vi.        A medicine is the end product of a chain of chemical reactions.

Q2. True/False

                           i.        Formation of manure from leaves is a physical change. False

                          ii.        Iron pipes coated with zinc do not get rusted easily. True

                         iii.        Iron and rust are the same substances. False

                         iv.        The chemical name of baking soda is Sodium hydrogencarbonate. True

                          v.        Changes in which new substances are formed are called chemical changes. True

Q3. What type of change is crystallisation?

Ans. It is a physical change.

Q4. What type of change is involved in rusting of iron?

Ans.  Rusting of iron is a chemical change.

Q5. Write one property of stainless steel.

Ans. It does not rust.

Q6. What type of change is formation of manure?

Ans. Formation of manure is a chemical change.

Q7. Which of the two is permanent change chemical change or physical change?

Ans. Chemical change is a permanent change.

Q8. What do you understand by chemical change?

Ans. A change in which one or more new substances are formed is called a chemical change.

Q9. State the conditions necessary for rusting of iron?

Ans. For rusting, the presence of both oxygen and water (or water vapour) is essential.

Q10. What is galvanisation?

Ans. The process of depositing a layer of metal like zinc or chromium on iron is called galvanisation.

Q11. What is added to steel to make it stainless?

Ans. Stainless steel is made by mixing iron with carbon and metals like chromium, nickel and manganese.

Q12. Why formation of manure from leaves is a chemical change?

Ans. Formation of manure from leaves is a chemical change because manure formed has a different composition from leaves.

Q13. Why souring of milk is a chemical change?

Ans. Souring of milk is a chemical change because it results in formation of new substance.

Q14. What is rust?

Ans. If a piece of iron is left in the open for some time, it acquires a film of brownish substance. This substance is called rust.

Q15. What is blue vitriol?

Ans. Crystals of copper sulphate pentahydrate are blue in colour. So, it is commonly known as blue vitriol.

Q16. Name the two methods by which rusting of iron can be prevented.

Ans. Two methods by which rusting of iron can be prevented are by painting or greasing and by galvanizing.

Q17. What happens when baking soda is treated with vinegar?

Ans. Vinegar (Acetic acid) + Baking soda (Sodium hydrogencarbonate) → Carbon dioxide + other substances

Q18. Which technique is better for obtaining sugar from sugar solution?

Ans. Crystallization is considered as a better technique for obtaining sugar from sugar solution.