KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Students can Download Science Chapter 6 Physical and Chemical Changes Questions and Answers, Notes Pdf, KSEEB Solutions for Class 7 Science helps you to revise the complete Karnataka State Board Syllabus and to clear all their doubts, score well in final exams.

Karnataka State Syllabus Class 7 Science Chapter 6 Physical and Chemical Changes

Class 7 Science Physical and Chemical Changes Textbook Exercise Questions and Answers

Question 1.
Classify the changes involved in the following processes as physical or chemical changes.
Answer:
(a) Photosynthesis
Answer:
Chemical change
(b) Dissolving sugar in water
Answer:
Physical change
(c) Burning of coal
Answer:
Chemical change
(d) Melting of Wax
Answer:
Physical change
(e) Beating aluminium to make aluminium foil
Answer:
Physical change
(f) Digestion of food
Answer:
Chemical change
KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Question 2.
State whether the following statements are true or false. In case a statement is false, write the corrected statement in your notebook?

  1. Cutting a log of wood into pieces is a chemical change. (True/False).
  2. The formation of manure from leaves is a physical change (True/False).
  3. Iron pipes coated with zinc do not get rusted easily. (True/False).
  4. Iron and rust are the same substances. (True/False).
  5. Condensation of steam is not a chemical change. (True/False).

Answer:

  1. False
  2. False
  3. True
  4. False
  5. True

Question 3.
Fill in the blanks in the following sentences:

  1. When carbon dioxide is passed through lime water, it turns milky due to the formation of
  2. The chemical name of baking soda is
  3. Two methods by which rusting of iron can be prevented are and
  4. Changes in which only properties of a substance change are called physical changes.
  5. Changes in which new substances are formed are called changes.

Answer:

  1. Calcium carbonate.
  2. Sodium hydrogen carbonate.
  3. galvanization, painting.
  4. physical.
  5. chemical.

KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Question 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.
Answer:
It is a chemical change. Baking soda reacts with lemon juice (Citric acid) and evolves carbon dioxide in the form of bubbles along with other products.

Question 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.
Answer:
When a candle burns, both physical and chemical changes take place.
Physical changes: On heating, candle wax gets melted is a physical change since it again turns into said wax on coding.
Chemical changes: The wax near to flame bums and gives new substances like carbon Dioxide, water vapour, heat and light. Cooking of food, is another example where both physical and chemical changes occurs.

Question 6.
How would you show that setting of curd is a chemical change?
Answer:
Curd is formed from the milk. It is a new substance which has different properties from milk. We cannot get back milk from curd. Hence, setting of curd is a chemical change.

Question 7.
Explain why burning of wood and cutting it into small pieces are cosidered as two different types of changes.
Answer:
Burning of wood is a chemical change. Carbon dioxide, water vapour and coal are formed on burning of wood. Whereas cutting of wood is a physical change because there is no new substance formed. The composition and properties of wood remain same.

KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Question 8.
Describe how crystals of copper sulphate are prepared.
Answer:
Take water in a beaker and add few drops of dilute sulphuric acid. Heat the water. Then, add copper sulphate powder and stir continuously till no more copper sulphate dissolves. Filter the solution and allow the filterate to cool. The blue crystals of copper sulphate will be formed after sometime.

Question 9.
Explain how painting of an iron gate prevents it from rusting.
Answer:
Iron gets rusted in presence of oxygen and moisture. Painting of iron gate prevents its surface coming in contact with oxygen and mositure. Thus, painting prevents it from rusting.

Question 10.
Explain why the rusting of iron objects is faster in coastal areas than in deserts.
Answer:
Rusting requires the presence of oxygen and moisture to take place. Coastal areas have moist air and deserts have dry air in the atmosphere. Hence, the process of rusting is faster in coastal areas than in deserts.

KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

Question 11.
The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder it exists 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,
(ii) Process-B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(ii) Process-B is a chemical change.

Question 12.
Anaerobic bacteria digest animal waste and produce biogas (change-A). The biogas is then burnt as fuel (change-B). The following statements pertain to these changes. Choose the correct one.
(i) Process-A is a chemical change.
(ii) Process-B is a chemical change.
(iii) Both processes A and B are chemical changes.
(iv) None of these processes is a chemical change.
Answer:
(iii) Both processes A and Bare chemical changes.

KSEEB Solutions for Class 7 Science Chapter 6 Physical and Chemical Changes

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