CBSE Class 7 Science Physical And Chemical Change Worksheet

Physical and chemical changes

ACTIVITY- 6.1 : Cutting of paper is a physical change. 

Question 1- Mention whether the cutting is reversible or irreversible change.
Answer- Irreversible change.

Question 2- Is the cutting of paper a physical or a chemical change?
Answer- Physical change.

ACTIVITY- 6.2 : Crushing of chalk is physical change. 

Question 1- Can you recover chalk from dust?
Answer- Yes.

Question 2- Does chalk powder dissolve in water?
Answer- No.

Question 3- What is the nature of above change? Is it physical or chemical?
Answer- Physical change.

ACTIVITY- 6.3: Change in a state of water is a physical change. 

Question 1- Ice melts into water with …………… in temperature.
Answer- Increase.

Question 2- Water changes to ice with …………… in temperature.
Answer- Decrease.

ACTIVITY- 6.4: Change in a state of water is a physical change. 

Question 1- What is evaporation?
Answer- Process of converting liquid into its vapour form is known as evaporation.

Question 2- Define condensation.
Answer- Process of converting vapours into its liquid form is known as condensation.

Question 3- Water changes into gaseous form with ………. in temperature.
Answer- Increase.

Question 4- Water changes from gaseous state to liquid state with ………… in temperature.
Answer- Decrease.

ACTIVITY- 6.5: Colour change is a physical change. 

Question 1- Which colour do you notice on heating the free end of hacksaw blade?
Answer- It turns orange/red.

Question 2- Is this physical change reversible or irreversible?
Answer- Reversible.

Question 1- Define a physical change .
Answer- The change in physical properties like state, length, position, colour, shape etc. is known as a physical change.

Question 2- Is a new substance formed during a physical change?
Answer- No.

Question 3- Explain any two examples of physical change from your surroundings.
Answer- Converting water into ice and melting of candle’s wax are physical changes.

ACTIVITY- 6.6 : Burning of magnesium ribbon is a chemical change. 

Question 1- What type of metal oxide is formed on burning of magnesium ribbon?
Answer- Basic.

Question 2- What is the colour of magnesium oxide formed on heating magnesium?
Answer- White.

ACTIVITY- 6.7: Reaction of copper sulphate with iron is a chemical change.

Question 1- What is the common name of copper sulphate?
Answer- Blue vitriol.

Question 2- Write the colour and chemical formula of ferrous sulphate.
Answer- Light green ; FeSO₄.

ACTIVITY- 6.8: Evolution of gas is a chemical change. 

Question 1- What is the formula of lime water?
Answer- Ca(OH)₂.

Question 2- How the presence of CO₂ gas can be detected?
Answer- Carbon dioxide (CO₂) gas turns lime water milky.

Question 1- What is a chemical change? 
Answer- A change in which one or more new substances are formed is called a chemical change.

Question 2- Write two observations to see chemical change.
Answer- (1) Evolution of heat or light, (2) Evolution of a gas.

Question 3- What is lime water?
Answer- Aqueous solution of calcium hydroxide-Ca(OH)₂.

Question 4- What happens when carbon dioxide is passed through lime water?
Answer- Carbon dioxide (CO₂) gas turns lime water milky due to the formation of calcium carbonate.

Question 5- Name the gas evolved when acetic acid (vinegar) reacts with baking soda.
Answer- Carbon dioxide (CO₂) gas.

Question 6- What is the colour and formula of copper sulphate?
Answer- Colour- Blue ; Formula- CuSO₄.

Question 7- Name some compounds formed as a result of chemical reactions.
Answer- Calcium hydroxide, Calcium carbonate, Carbon dioxide etc.

Question 8- In chapter 5, you neutralized an acid with a base. Is neutralization a chemical change?
Answer- Yes.

ACTIVITY- 6.9: Preparation of crystals of copper sulphate. 

Question 1- What is end product in the process of crystallization?
Answer- Pure crystals of the given salt.

Question 2- When will you stop dissolving copper sulphate powder to hot water?
Answer- Till no more powder can be dissolved i.e. to get saturated solution.

EXERCISE

1- Fill In The Blanks.

(i) A change in which only physical properties of a substance are changed is a physical change.
(ii) Changes that lead to formation of new substances are called chemical changes.
(iii) Fossil fuels produce carbon dioxide gas on burning.
(iv) When carbon dioxide is passed through lime water, it turns milky.
(v) Galvanization is the method for the prevention of rusting of iron objects.

2- Match The Column ‘A’ With Column ‘B’.
Column A                                          Column B
(i) Physical change                        (a) Galvanization
(ii) Chemical change                     (b) Formation of a new substance
(iii) Prevention from rusting           (c) Mixing of vinegar and baking soda
(iv) Evolution of carbon dioxide      (d) Reversible change
Ans.(i) -d , (ii)-b , (iii)-a , (iv)-c  

3. Choose The Correct Answer.

Question. The example of chemical change is:
a) Eruption of volcano
b) burning of candle
c) cooking of food
d) all of the above 
Ans.d) all of the above

Question. When acetic acid is mixed with baking soda, the gas evolved is:
a) hydrogen
b) oxygen
c) carbon dioxide
d) carbon mono oxide
Ans.c) carbon dioxide

Question. For rusting of iron objects, the essential requirement is:
a) air (oxygen)
b) moisture (water)
c) open surface of object
d) All of the above
Ans.d) All of the above

Question. For prevention of rust, we use:
a) A coat of oil and grease
b) A coat of paint
c) galvanization
d) all of the above
Ans.d) all of the above

Question. The chemical formula of rust is:
a) Fe₂O₃
b) FeCO₃
c) Fe₂O₃.xH₂O 
d) FeO₃.xH₂O
Ans.c) Fe₂O₃.xH₂O 

4- Write True Or False.

(i) Cutting a log of wood into pieces is a chemical change.     (False)
(ii) Formation of manure from leaves is a physical change.    (False)
(iii) Iron pipes coated with zinc do not get rusted easily.         (True)
(iv) Iron and rust are the same substances.                           (False)
(v) Condensation of steam is not a chemical change.            (True)

5- Very Short Answer Type Questions.

Question. What is rust? Write its chemical formula.
Answer- On reacting with air and moisture, a brown-red coloured layer is formed on iron objects, this layer is known as rust. Chemical formula of rust is Fe₂O₃.xH₂O.

Question. Write the conditions necessary for rusting of iron.
Answer- Presence of: (1) Air (oxygen), (2) moisture (water), (3) open surface of an iron object.

Question. Why are iron objects painted frequently?
Answer- For rusting of iron, contact of air and water is necessary. So iron objects are painted to prevent the contact of iron with air and moisture.

Question. What is galvanization?
Answer- The process of depositing a layer of non-reactive metal (like zinc) over the surface of iron is known as galvanization.

Question. Name two metals which are deposited on the surface of iron objects during the process of galvanization.
Answer- Zinc or aluminium.

Question. Burning of candle is an example of which type of change-physical or chemical change? Give reasons.
Answer- Burning of candle is a chemical process as it produces gases (new substance). Besides this melting of wax of candle is a physical change.

Question. Why burning of fireworks s harmful?
Answer- Because burning of fireworks may cause blast, which produce many harmful gases.

Question. What is crystallization?
Answer- Method of getting pure solid from an impure sample of solid by making crystals is known as crystallization.

6- Short Answer Type Questions.

Question. Mixing of baking soda or vinegar is a chemical change or a physical change? Discuss.
Answer- Chemical change, because a new substance carbon dioxide gas is produced.

Question. Explain how cutting and burning of wood are different type of change?
Answer- Cutting of wood is a physical change, because here only shape and size of wood are changed. But burning of wood is a chemical change, because here a new substance carbon dioxide gas is produced.

Question. What will happen when carbon dioxide is passed through lime water?
Answer- Carbon dioxide (CO₂) gas turns lime water milky due to the formation of calcium carbonate.

Question. Why does the colour of copper sulphate (CuSO₄) solution change, when an iron nail is dipped into it? Write chemical equation also.
Answer- When iron nails are dipped in copper sulphate solution, solution turns green from blue, because more reactive iron displaces copper forming green coloured iron sulphate. Chemical equation is as follows:
Fe + CuSO₄(aq)  → FeSO₄(aq) + Cu
Iron nails + Copper sulphate solution  →  Iron sulphate + copper.
                  (blue)                                 (light green)

Question. Magnesium ribbon is burnt and the ash formed is mixed with water. Now answer the following:

(a) Write equation for the burning of magnesium.
Answer- 2Mg + O₂ → 2MgO

(b) What will happen when the mixture of ash and water is added to (1) blue litmus solution and (2) red litmus solution?
Answer-
(1) Blue litmus solution will remain blue.
(2) Red litmus solution will turn blue.

(c) Name the substance formed by mixing ash and water. Is it acidic or basic?
Answer- Magnesium oxide solution is basic.

7- Long Answer Type Questions.

Question. What are physical and chemical changes? Write differences between physical and chemical changes.
Answer-
Physical changes                                                       Chemical changes
1. The change in physical properties like state,       1. A change in which one or more new substances are formed is called a chemical change.
length, position, colour, shape etc. is known as a
physical change.
2. Not any new substance is formed.                     2. New substance is formed.
3. For example: Melting of ice.                               3. For example: Burning of paper.

Question. What do you understand by rusting of iron? Write the necessary conditions required for rusting of iron objects. How rusting of iron and iron objects can be prevented?
Answer- Rusting of iron- On reacting with air and moisture, a brown-red coloured layer is formed on iron objects; this process is known as rusting. Necessary conditions for rusting- Presence of: (1) Air (oxygen), (2) moisture (water), (3) open surface of an iron object.
Prevention of rusting- (1) By greasing or oiling, (2) By painting, (3) By galvanization.

Question. Give detail of process of crystallization of copper sulphate (CuSO₄).
Answer- Take 200ml of water in a beaker and add a few drops of dilute sulphuric acid into it. Heat the water.When it starts boiling, copper sulphate powder is added slowly while stirring continuously to make a saturated solution. The solution is filtered and allowed to cool down. Crystals of copper sulphate slowly form at the bottom of the beaker.

More Question

Fill in the blanks :

1. Changes that lead to the formation of new substances are called ________________

2. Melting of candle wax is a______________ change but its burning is a ______________ change.

3. Growth of a plant is a ____________ change while formation of clouds is a _____________ change.

4. A brown layer formed when an iron article is left exposed in air in an open area is called ___________

5. Large crystals of pure substance are obtained by _____________

6. The brown layer deposited on an iron nail dipped in copper sulphate solution is due to ______________

Name the following

1. Write the chemical formula of lime water.

2. Write the chemical name of Mg(OH)₂

3. Write the chemical name and formula of rust.

4. Write the chemical name of blue vitriol.

Complete the following chemical reactions :

1. Magnesium oxide (MgO) + water (H₂O) ______________

2. Iron (Fe) +oxygen (O₂ ) + water (H2O) ________________

3. Carbondioxide ( CO₂) + Lime water [Ca(OH)₂] _______ + _______

4. Copper sulphate + Iron ______________ + _________________

Define

1. Crystallization

2. Galvanization

Distinguish between

1. Physical change and chemical change

Q1 Circle the odd one out from the following sets:

a) Souring of milk, Burning of a candle, Melting of ice, Ripening of fruits

b) New substances, Change of shape, Irreversible, Permanent

c) Evaporation of water to form clouds, Bursting of a cracker, Baking of a cake, Germination of seeds

d) Tearing a paper, Writing on a paper, Making paper boats from a piece of paper, Burning a paper

e) Breaking a glass, Photosynthesis of plants, Making milk shakes, Switching the fan

Q2 Justify the following changes as Physical or Chemical

i. Eating of vada.

ii Beating an egg to make a cake.

iii. Separating sand from gravel at the building site.

iv. Nita fries an egg.

v Burning of fuel in a car

Q3. Match the following:

Column A Column B

i. Rusting a. Physical properties may change

ii. Chemical change b. Evaporation

iii. Physical change c. Oxidation

iv. Crystallisation d. Moisture

v. Galvanisation ` e. Neutralisation reaction

vi. Cut vegetables f. Usually irreversible

vii. Vinegar + Baking soda g. Displacement reaction

Q4 . Answer the following questions in brief:

1. State four characteristics of a physical change.

2. State four characteristics of a chemical change.

3. Give an example of a chemical change in which we observe change in colour during the reaction.

4.Mention the factors that cause rusting of iron.

5. Why do cut vegetables take up a brown colouration when exposed in air?

6. Differentiate between physical and chemical changes. Give two examples for each.

7. Mention two irreversible physical changes. Explain why those changes are physical even though they are irreversible.

8. Why does rusting occur? Give four ways to prevent rusting.

9. What do you observe when you mix vinegar and baking soda? How do you perform a test for the gas released during the reaction?

10. What is crystallisation? How can we get crystals of urea from its solution?

Physical and Chemical Changes

1.Can deforestation be considered as a reversible change?

2.What is the chemical name of Baking Soda?

3.What is Rust?

4.What type of change is photosynthesis?

5.Fraction of ship's iron has to be replaced every year because-
(A) It prevents rusting of iron.
(B) Its color fades away.
(C) Ship can move properly in water only after replacement.
(D) All the above.

6.When magnesium oxide (MgO) reacts with water to form magnesium hydroxide [Mg(OH)₂], a base, it turns ......................... litmus to .......................
(A) Blue, red
(B) Blue, colourless
(C) Red, blue
(D) Colourless, blue

7.What do you understand by physical properties of a substance?

8.When vinegar reacts with baking soda the gas evolved is-
(A) Hydrogen.
(B) Oxygen.
(C) Carbon dioxide.
(D) Nitrogen dioxide.

9.When copper sulphate reacts with iron, green coloured ........................ solution and brown coloured ....................... deposition is formed
(A) Iron oxide, copper sulphide
(B) Iron sulphate, copper
(C) Iron sulphate, copper oxide
(D) Iron sulphide, copper oxide

10.Ozone layer is present in-
(A) Atmosphere.
(B) Clouds.
(C) Soil.
(D) Water.

11.Complete the reaction-
Carbon dioxide + Lime water →........................ + .................................
(A) Calcium carbonate, water
(B) Calcium hydroxide, oxygen
(C) Calcium oxide, water
(D) Calcium carbonate

12.The process of obtaining pure crystals of copper sulphate from copper sulphate solution is known as-
(A) Galvanization.
(B) Evaporation.
(C) Crystallization.
(D) Rusting.

13.While preparing copper sulphate crystals from copper sulphate solution, dilute sulphuric acid is used instead of concentrated sulphuric acid, because-
(A) Concentrated sulphuric acid is corrosive in nature.
(B) Dilute sulphuric acid makes large crystals.
(C) Concentrated acid is ineffective.
(D) Both (a) & (b).

14.Select thechemical changes from the following options:
(i) Copper metal drawn into wires. (ii) Burning of paper. (iii) Digestion of food. (iv) Breaking of glass.
(A) (i), (ii) & (iii).
(B) (ii) & (iii).
(C) (i) & (iv).
(D) (i), (iii) & (iv).

15.To prevent iron from rusting, a coating of this metal is deposited-
(A) Calcium.
(B) Chromium.
(C) Sodium.
(D) Potassium.

16.Chemical change may be accompanied by:
(i) Production of sound. (ii) Heat and light. (iii) Change in mass. (iv) Change in color.
(A) (i), (ii) & (iii).
(B) (ii) & (iv).
(C) (i) only.
(D) (i), (ii) & (iv).

17.Baking soda is common name for-
(A) Sodium carbonate.
(B) Sodium hydrogen carbonate.
(C) Calcium carbonate.
(D) Sodium hydroxide.

18.Give 2 examples of physical change.

19.Is crystallization an example of physical change?

20.What is a chemical change?

21.Select the correct alternative(s).
(i) Melting of ice is a physical change.
(ii) A physical change is change in physical properties of asubstance.
(iii) A physical change is always irreversible in nature.
(iv) Burning of candle is an example of physical change.
(A) (i) & (ii).
(B) (i) & (iv).
(C) (i), (ii) & (iv).
(D) (ii) & (iii).

22.When magnesium ribbon is burnt, a brilliant ................ flame is observed.
(A) Yellow
(B) Blue
(C) White
(D) Green

23.Pick out physical changes from the following:
(i) Rusting of iron.
(ii) Dissolving salt in water.
(iii) Change of water to ice.
(iv) Cooking of food.
(A) (i) & (ii).
(B) (ii) & (iii).
(C) (i), (ii) & (iii).
(D) (iii) & (iv).

24.Blue vitriol is the common name of-
(A) Copper sulphate.
(B) Copper oxide.
(C) Copper hydroxide.
(D) Magnesium sulphate.

25.The gas in the atmosphere which acts as a natural shield against ultra violet radiations is-
(A) Oxygen.
(B) Sulphur dioxide.
(C) Hydrogen.
(D) Ozone.

26.The elements required for rusting of iron.
(A) Oxygen and moisture.
(B) Only oxygen.
(C) Hydrogen and oxygen.
(D) Only water vapours.

27.During rusting the layer which is deposited on the surface of iron is
(A) Fe₂O
(B) FeO
(C) Fe₂O₃.xH₂O
(D) Fe(OH)₃

28.Stainless steel is made by mixing iron with carbon and metals like......................
(A) Magnesium, sodium, calcium.
(B) Chromium, Nickel, Manganese.
(C) Cobalt, Potassium, Iron.
(D) Potassium, Sodium, Chromium.

29.Lime water turns milky when .............. gas is passed through it.
(A) Carbon dioxide
(B) Hydrogen
(C) Oxygen
(D) Nitrogen dioxide

30.The process of depositing layer of zinc on iron is known as-
(A) Galvanization.
(B) Crystallization.
(C) Rusting.
(D) Layering.

31.Burning is a chemical change and is always accompanied by production of-
(A) Sound.
(B) Heat.
(C) Gas only.
(D) Sound & heat.

32.Explosion of a firework produces-
(A) Heat & light.
(B) Heat only.
(C) Gases only.
(D) Heat, light, sound & unpleasant gases.

33.When magnesium ribbon burns in air, it leaves an ash which is-
(A) Mg(OH)₂
(B) MgO
(C) MgS
(D) MgSO₄

34.For rusting-
(A) Presence of water is essential.
(B) Presence of oxygen is essential.
(C) Presence of both water and oxygen is essential.
(D) Presence of air is essential.

35.Stainless steel is resistant to rusting, though it is made from iron. Why?
(A) Because it is steel.
(B) Because it is resistant to stains.
(C) Because it is made from iron, chromium, nickel and manganese.
(D) Because it is galvanised.

36.Why are the water pipes in our homes galvanised?
(A) To prevent rusting of iron.
(B) To coat them with a layer of zinc.
(C) To prevent their leakage and breakage.
(D) All of them.

<2M>

37.Can we call the breaking down of ozone a chemical change? Why?

38.How would you show that setting of curd is a chemical change?

39.What is the standard test for carbon oxide?

40.Give the chemical equations for rusting and chemical name for rust.

41.Explain how painting of an iron gate prevents it from rusting.

42.Explain why rusting of iron objects is faster in coastal areas than in deserts.

<3M>

43.What is the difference between physical change and chemical change? Give example.

44.Explain why burning of wood and cutting it into small pieces are considered as two different types of changes?

45.What is rusting? How do we prevent rusting?

46.When a candle burns, both physical and chemical changes take place. Identify these changes.

Give another example in which both the chemical and physical changes take place.

47.What happened when a pinch of baking soda is added to vinegar. Write the equation also.

48.What are the various characteristics that may accompany a chemical change?

<5M>

49.Describe how crystals of copper Sulphate are prepared?

50.Explain the formation of Magnesium hydroxide from a piece of magnesium ribbon along with corresponding equations.

51.Describe an activity to show the formation of iron sulphate when an iron nail is dropped into copper sulphate solution. Mention the equation too.

Q1 Circle the odd one out from the following sets:

a. souring of milk, burning of a candle, melting of ice, ripening of fruits

b. new substances, change of shape, irreversible, permanent

c. evaporation of water to form clouds, bursting of a cracker, baking of a cake, germination of seeds

d. tearing a paper, writing on a paper, making paper boats from a piece of paper, burning a paper

e. breaking a glass, photosynthesis of plants, making milk shakes, switching the fan

Q2 Justify the following changes as Physical or Chemical:

i. eating of vada.

ii. Beating an egg to make a cake.

iii. Separating sand from gravel at the building site.

iv. Nita fries an egg.

v. A petrol can is left open in the garage. The vapour fills the garage.

Q3. Match the following:

   Column A                                                 Column B

i. Rusting                                          a. Physical properties may change

ii. Chemical change                         b. Evaporation

iii. Physical change                          c. Oxidation

iv. Crystallisation                              d. Moisture

v. Galvanisation                                e. Neutralisation reaction

vi. Cut vegetables                             f. Usually irreversible

vii. Vinegar + Baking soda                g. Displacement reaction

Q4 E. Answer the following questions in brief:

1. State four characteristics of a physical change.

2. State four characteristics of a chemical change.

3. Give an example of a chemical change in which there is a change of colour that takes place.

4. Recall the factors that cause rusting to occur.

5. Why do cut vegetables take up a brown colouration when exposed in air?

6. Differentiate between physical and chemical changes. Give two examples for each.

7. Mention two irreversible physical changes. Explain why those changes are physical even though they are irreversible.

8. Why does rusting occur? Give four ways to prevent rusting.

9. What do you observe when you mix vinegar and baking soda? How do you perform a test for the issuing gas?

10. What is crystallisation? How can you get crystals of urea from its solution?

Fri – Science

1. Classify the following as physical or chemical changes

a. Photosynthesis

b. Melting of wax

c. Digestion of food

d. Burning of coal

2. Name the following

a. Powdery ash formed on burning magnesium

b. Process of depositing zinc on iron.

3. Rusting of iron is faster in coastal areas. Why? explain

4. Define crystallization.

Fill in the blanks:

1. Changes that lead to the formation of new substances are called ________________

2. Melting of candle wax is a______________ change but its burning is a ______________ change.

3. Growth of a plant is a ____________ change while formation of clouds is a _____________ change.

4. A brown layer formed when an iron article is left exposed in air in an open area is called ___________

5. Large crystals of pure substance are obtained by _____________

6. The brown layer deposited on an iron nail dipped in copper sulphate solution is due to ______________

Name the following

1. Write the chemical formula of lime water.

2. Write the chemical name of Mg(OH)2

3. Write the chemical name and formula of rust.

4. Write the chemical name of blue vitriol.

Complete the following chemical reactions :

1. Magnesium oxide (MgO) + water (H₂O) ______________

2. Iron (Fe) +oxygen (O₂ ) + water (H₂O) ________________

3. Carbondioxide ( CO₂) + Lime water [Ca(OH)₂] _______ + _______

4. Copper sulphate + Iron ______________ + _________________

Define
1. Crystallization
2. Galvanization

Distinguish between
1. Physical change and chemical change

Q1. What is a chemical change? Give two examples.

Q2. Name two agents which cause corrosion.

Q3. What is harmful effect of corrosion?

Q4. How do you show that curdling of milk is a chemical change?

Q5. In what way oiling & greasing help to prevent rusting?

Q6. What is crystallization & in what way is the process helpful to us?

Q7. State four differences between physical & chemical changes.

Q8. Explain how burning of paper is different from tearing it?

Q9.What is rusting? What are the conditions necessary for rusting? How can rusting be prevented?

Q10.When a candle burns, both physical & chemical changes take place. Identify these changes.

Q11. When Magnesium is burned in air, a powdery ash X is obtained. X on dissolving in water forms Y. What are X & Y?

Q12. How is impure common salt purified?

Q13.Classify the following as physical or chemical change:

a) stretching of rubber band

b) photosynthesis in plants

c) formation of curd from milk

d) burning of leaves

e) magnetization of iron piece

f) respiration in living organisms

g) digestion of food

h) melting of wax

i) formation of clouds

Q14. How do you show that melting of ice is a physical change?

Q15.Name the gas evolved when vinegar is added to baking soda? How do you identify this gas?

Q16. What happens when an iron nail is put in coppers sulphate solution? Explain.

Answer the following questions:

Q.1 Explain why a bicycle made of iron rusts.

Q.2 What happens when we add a pinch of baking soda to a teaspoonful of vinegar.

Q.3 Explain the reason for the change in colour of the copper sulphate solution when a nail is dropped into it..

Q.4 How does the ozone layer protect us?

Q.5 Why does stainless steel not rust?

Q.6 Explain how burning of wood is a chemical change.

Q.7 What are the characteristics of a chemical change?

Q1) What is a physical change? Give examples.

Q2) What is a chemical change? Give examples.

Q3) Write three differences between a physical and a chemical change.

Q4) Classify the following changes as physical or chemical change:
i. Rusting of iron
ii. Burning of crackers
Iii Digestion of food
iv. Melting of ice
v. Chopping of wood
vi. Respiration
vii Growing of a seed into a plant
viii Dissolving sugar in water

Q5) When we put an iron nail in Copper Sulphate solution, we find that after some time the blue colour of the solution changes to green. Also, a deposition of a brown substance takes place on the iron nail.
i. Write the equation involved.
ii. Why does the colour of the solution change?
iii. What is the brown deposit on the iron nail?
iv. Is it a physical or a chemical change?

Q6) Give one standard test for Carbon Dioxide. Also write the equation involved. Is it a physical or a chemical change?

Q7) Define rusting. What are the conditions necessary for rusting?

Q8) What is rust? What is its chemical formula?

Q9) Define galvanisation. Why are the iron pipes in our homes galvanized?

Q10) Why does rusting take place faster near the coastal areas?

Q11) Explain two methods by which rusting of iron can be prevented.

Q12) Explain how painting of an iron gate prevents it from rusting.

Q13) Define crystallization.Is it a physical or a chemical change?

Q14) How is melting of wax different from burning of wax?

Q15) Explain why ozone layer in our atmosphere is regarded a protective shield?

Q16) Rewrite the following chemical changes with the help of chemical formulae:
(a). Magnesium + Oxygen ----------------> Magnesium oxide
(b). Magnesium Oxide + Water --------------> Magnesium hydroxide
(c). Copper sulphate + Iron ----------> Iron sulphate + Copper

Q.17) Ram and his neighbour Shyam have got their homes fenced with iron rods. Ram saw the next day that Shyam was painting the iron fence. Shyam suggested Ram to do the same to increase the longevity of iron rods by preventing corrosion. Ram argues that it is a waste of time and the iron rods are strong.

Answer the following questions
(i) Whose opinion is correct according to you? What values are promoted here?
(ii) Other than painting, what are the other ways to prevent corrosion?