Class 5 - General Science Key Points Notes
Punjab curriculum and textbook board (PCTB) Lahore
Chapter 5: Physical and Chemical Changes in Matter
Question and Answer through Lesson
Q1: What is Matter? or Define Matter?
Ans: Anything that has mass and occupies space is called matter.
Q2: Write the name of three states of matter?
Ans: The three physical states of matter are solid, liquid, and gas.
Q3: What are Physical Changes?
Ans: In physical changes, only the appearance of a substance/matter changes but chemical composition remains the same.
Q4: Explain Physical Changes by a sample experiment? Can physical changes be reversed?
Ans:
Procedure:
1. Take two to three spoons of salt in a clean beaker.
2. Pour half a cup of warm water into the dish and keep it stirring till all the salt dissolves.
3. Heat the beaker or dish till all the water evaporates as vapours.
Observation:
It is observed that salt is present in the dish.
Result:
The dissolving of salt in water is a physical change. It only changes the state of matter. But matter having new properties is not formed. The physical change can be reversed. As in this experiment, the salt remained there after the water evaporated as vapors.
Q5. Take a soft drink aluminium can. Then crush it with a hammer. Have you observed any change?
Ans:
When a soft drink aluminium can is crushed with a hammer. It has only squeezed (firmly pressed). Its shape has changed and no new matter is formed. So it is a Physical change.
Q6. Explain with an example the changes in states of matter with temperature.
Ans:
On heating solid wax in a beaker or dish melted and became liquid. The liquid wax freezes on cooling and changes to solid again. The changes that occur in wax are related to the physical state of matter.
Q7. Define the process of melting and explain with an example.
Ans:
Definition: The process of change of a liquid state into a solid state by absorption of heat is called melting.
Explanation:
The particles/atoms in a solid keep on vibrating but remain at fixed positions. When a solid gets heat, its particles start vibrating faster and do not remain in their position. The forces of attraction between them become weaker and they move away from each other. Thus, a solid is changed into its liquid state.
Examples:
1. On heating solid wax in a beaker or dish melted and became liquid.
2. When a solid piece of ice absorbs heat, it becomes water by melting.
Q8. Define the process of freezing and explain with an example.
Ans:
Definition: The process of change of a solid state into a liquid state by releasing heat is called melting.
Explanation:
When water is kept in a freezer. During this process, heat is lost from water. As a result, the movement of its particles/atoms becomes slower and they come closer to each other. The force of attraction between particles becomes stronger. Thus the liquid state is changed into a solid state.
Examples:
1. On cooling liquid wax became solid.
2. When water is kept in a freezer. It becomes solid.
Q9. Define the process of boiling and explain with an example.
Ans:
Definition: The process of change of a liquid state into a vapour or gas state by absorption heat is called boiling.
Explanation:
When a liquid is heated continuously, the movement of its particles becomes faster. The space between the particles increases. Due to this, the liquid is changed to vapours or gas. The boiling of a liquid requires a high temperature.
Examples:
1. On continuous heating, water in a beaker or dish boiled and changed into vapour or gas state.
Q10. Define Evaporation.
Ans: The change of water into water vapours is called evaporation.
Examples:
1. Wet clothes are dried due to evaporation.
Q11. Can evaporate at all temperatures? Or Can water evaporate from the snowy surface?
Ans: Yes, Water can evaporate at all temperatures, and at high temperatures, the process of evaporation becomes rapid. The process of evaporation occurs continuously on the surfaces of canals, lakes, rivers, oceans, etc. This process also takes place from the snow surface and from the leaves of plants.
Q12. Define Condensation. Explain with an example.
Ans: The change of vapour or gaseous state of matter into a liquid state is called evaporation.
Explanation:
When cold water or a cold drink is poured into a glass, water drops appear at the external (outer) surface of the glass. It happened due to the water vapours present in the air touching the cold external surface of the glass, they lose heat. As a result, these water vapours change into liquid and stick to the external surface of the glass.
Q13. Define a Solution.
Ans:
When a solid or liquid thing is placed in water, its particles dissolve uniformly in water and form a mixture called a solution.
Q14. State the component of the solution.
Ans:
There are two important components of a solution.
1. Solute: The substance that dissolves in water and is in less quantity is called solute e.g, sugar, salt.
2. Solvent: The substance that dissolves a solute and is in more quantity is called solvent Le, water, milk.
Q15. What is a Solute:
Ans: The substance that dissolves in water and is in less quantity is called solute e.g., sugar, salt.
Q16. What is a Solvent:
Ans:
The substance that dissolves a solute and is in more quantity is called solvent Le, water, milk, etc.
Q.17 How can the rate of dissolving of a solute in solvent be increased?
Ans:
Many things can dissolve in water and form a solution. The rate of dissolving of solute (e.g. salt, sugar ) in a liquid (water) can be increased in the following ways:
1. By striving:
The dissolving of solute (e.g. sugar, salt, etc.) by stirring in solvent (water) dissolves faster, whereas without striving dissolves slowly.
2. Increasing Temperature:
The rate of dissolving of solute (e.g. salt, sugar) in a liquid (e.g. water) can be increased by increasing temperature.
Examples: Salt or Sugar can be dissolved in hot water more quickly than in cold water.
3. Decreasing the Size of Particles:
Decreasing the size of particles of solute will dissolve in solvent soon.
Examples: The powdered sugar or salt can dissolve more quickly than a cube of sugar or salt.
Q18. Explain with an experiment that the rate of dissolving of a solute in a solvent is increased by Striving.
Ans:
Procedure:
1. Take two beakers or glasses. Mark them as A and B.
2. Add a spoon of sugar (solute) to both beakers.
3. Then pour a cup of water (solvent) into both beakers.
4. Stir sugar in beaker A with a glass rod. Do not stir sugar in beaker B.
Observation:
The dissolving sugar by stirring in solvent (water) dissolves faster in beaker A, whereas without striving dissolves slowly.
Result:
The dissolving of solute (e.g. sugar, salt, etc.) by stirring in solvent (water) dissolves faster, whereas without stirring in a beaker B dissolves slowly.
Q19. Explain with an experiment that the rate of dissolving of a solute in a solvent is increased by increasing the temperature.
Ans:
Procedure:
1. Take two beakers or glasses. Mark them as A and B.
2. Pour one cup of hot water (solvent) into beaker A and pour a cup of cold water (solvent) into beaker B.
3. Put a spoon of sugar or a sugar cube in both beakers simultaneously.
Observation:
A spoon of sugar or a sugar cube dissolved in beaker A containing hot water more quickly than in beaker B containing cold water.
Result:
Solutes (Sugar) can be dissolved in hot water more quickly than in cold water.
Q20. Explain with an experiment that the rate of dissolving of a solute in a solvent is increased by decreasing the size of particles of solute.
Ans:
Procedure:
1. Take two beakers or glasses. Mark them as A and B.
2. Put a spoon of powdered sugar or grains of sugar in glass A and a sugar cube in glass B.
3. Now pour a cup of water in both glasses.
Observation:
The powdered sugar or grains of sugar dissolved in beaker A more quickly than in beaker B containing a cube of sugar.
Result:
The dissolution of any solute depends on the size of its particles. The solutes which are made of small particles (e.g. powder sugar), dissolve in solvent faster as compared to the solutes made of large particles (e.g., sugar cube).
Q21. What is a dilute and concentrated Solution? explain with an experiment?
Ans:
Dilute Solution: A solution having a minor quantity of solute is called a dilute Solution
Concentrated Solution: A solution having more quantity of solute is called a concentrated Solution
Experiment:
Procedure:
1. Pour an equal quantity of water into five glasses.
2. Do not pour anything into the glass 1. Pour one spoon of colored drink into glass 2, two spoons into glass 3, three spoons into glass 4, and four spoons into glass 5.
Observation:
The light-colored glass shows dilute solutions while the darkest-coloured glass shows concentrated solutions
Result:
Less solute in a solvent is a dilute solution while more quantity of solute in a solvent becomes the concentrated solution.
Q22. What is a chemical change in matter?
Ans: In chemical change both the appearance and composition of substance/matter change.
Examples: Decaying of material, Burning of wood, etc. are chemical changes.
Q23. List some examples of chemical changes in matter in everyday life.
Ans:
If we look around, we will see plants, branches, vegetables, fruits, papers, and pieces of wood. These are being decomposed gradually. You must have seen rusted iron gates, doors, windows, and other things.
Q24. What is the decaying process?
Ans: The process of decomposing the dead bodies into simple components is called decaying. We see in our daily life that the remains of dead organisms and waste matter disappear gradually through decomposition. It is due to bacteria and fungi. They obtain their food by decomposing the dead bodies into simple components.
Q25. What is the burning process?
Ans: The fuel is burnt in the stove to cook food. When the fuel burns then we can see the flame. The flame develops during the combustion reaction. This is called burning e.g., the burning of coal, wood, paper, match sticks, etc.
Q26. What is rusting?
Ans: The change that occurs in the iron due to the action of oxygen and water is called rusting.
Rusting Reaction:
Iron + Oxygen + Water = Rusting
Q27. Explain rusting by setting up a sample experiment.
Ans:
Procedure:
1. Take three test tubes and mark them as A, B, and C.
2. Take water in test tube A and put a nail in it.
3. Take boiled water in test tube B and put a nail in it. Then put a few drops of oil on it.
4. Dry test tube C properly and put a nail in it.
5. Seal the mouth of the three test tubes with a cork and leave them for a few days in similar conditions.
Observation: The colour of test tube A changed.
Result: The colour of test tube A changed due to the presence of oxygen which reacted with iron in the presence of water.
Rusting Reaction:
Iron + Oxygen + Water = Rusting
Q28. Answer the following question of Activity No. 5.8 (page 57)
Ans: Test tune A
Q30. Why were boiled water and oil drops added to test tube B?
Ans: The boiled water added will remove the dissolved oxygen from the water and the layer of oil drop added will not allow the air to come into the water.
Q31. In which test tube was the change in the colour of the nail was not possible? Why?
Ans. Both in Test A and B
As we know that
Iron + Oxygen + Water = Rusting
Thus in test tube A rusting did not occur due to the absence of oxygen, while in test tube B rusting due to the absence of water.
Q32. How we can prevent iron material from rusting?
Ans: To prevent iron material from rusting, its surface is coated with paint, oil, or chromium.
Q. Differentiate between Physical and Chemical Changes.
Ans:
Physical changes:
1. No new material is formed with different properties
2. Physical change can be reversed
Examples:
On heating, the solid wax becomes liquid but remains a wax. On cooling the liquid wax becomes solid but remains a wax.
Chemical changes:
1. A change in which a new material (with different properties) is formed,
2. Physical change can not be reversed.
Examples:
The burning of paper is a chemical change as ash is formed in the process. The ash can't be reversed to its original state ie paper.
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