CBSE Class 7 Science Physical And Chemical Changes Assignment

Read and download free pdf of CBSE Class 7 Science Physical And Chemical Changes Assignment. Get printable school Assignments for Class 7 Science. Class 7 students should practise questions and answers given here for Chapter 6 Physical And Chemical Changes Science in Class 7 which will help them to strengthen their understanding of all important topics. Students should also download free pdf of Printable Worksheets for Class 7 Science prepared as per the latest books and syllabus issued by NCERT, CBSE, KVS and do problems daily to score better marks in tests and examinations

Assignment for Class 7 Science Chapter 6 Physical And Chemical Changes

Class 7 Science students should refer to the following printable assignment in Pdf for Chapter 6 Physical And Chemical Changes in Class 7. This test paper with questions and answers for Class 7 Science will be very useful for exams and help you to score good marks

Chapter 6 Physical And Chemical Changes Class 7 Science Assignment

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

Question 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.

Question 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)-(a)

Question 3. Choose The Correct Answer.

(i). The example of chemical change is:

a) Eruption of volcano

b) burning of candle

c) cooking of food

d) all of the above (✓)

(ii). When acetic acid is mixed with baking soda, the gas evolved is:

a) hydrogen b) oxygen

c) carbon dioxide (✓)

d) carbon mono oxide

(iii). 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 (✓)

(iv). 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 (✓)

(v). The chemical formula of rust is:

a) Fe₂O₃

b) FeCO₃

c) Fe₂O₃.xH₂O (✓)

d) FeCO₃.xH₂O

Question 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)

Question 5- Very Short Answer Type Questions.

(i) 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.

(ii) Write the conditions necessary for rusting of iron.

Answer- Presence of: (1) Air (oxygen), (2) moisture (water), (3) open surface of an iron object.

(iii) 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.

(iv) 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.

(v) Name two metals which are deposited on the surface of iron objects during the process of galvanization.

Answer- Zinc or aluminium.

(vi) 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.

(vii) Why burning of fireworks s harmful?

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

(viii) What is crystallization?

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

Question 6- Short Answer Type Questions.

(i) 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.

(ii) 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.

(iii) 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.

(iv) 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)

(v) 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.

Question 7- Long Answer Type Questions.

(i) 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

length, position, colour, shape etc. is known as a are formed is called a chemical change.

physical change.

2. Not any new substance is formed. 2. New substance is formed.

3. For example: Melting of ice. 5. For example: Burning of paper.

(ii) 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.

(iii) 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

Q.1 Fill in the blanks :

1. Photosynthesis is a _______________ change.

2. The micro-organisms which convert the dead plants and animals to humus are known as ______________.

3. The freezing point is ____0C at which water freezes.

4. Lactobacillus bacterium helps in the formation of ______________.

5. Galvanization is the process of coating iron objects with the layer of ________ metal.

Q.2 Correct the following sentences by replacing the highlighted words :

1. Change in the physical properties of a substance is termed as chemical change.