A. Multiple Choice Questions (MCQs) Scientific/ Practical skills:
1. Magnesium ribbon burns with____________ light forming ash.
(a) white (b) red (c) blue (d) green
Ans: a) white
2. Magnesium ribbon burns in air to form magnesium_______________.
(a) carbonate (b) bicarbonate (c) hydroxide (d) oxide
3. When an iron nail is kept in copper sulphate solution, the blue colour of copper sulphate solution change to_________________.
(a) red (b) orange (c) green (d) yellow
B. Very Short Answer Questions:
1. Give two examples of physical changes.
Ans: Two examples of physical changes are Melting of wax and formation of clouds.
2. What happens when magnesium oxide is dissolved in water?
Ans: When magnesium oxide is dissolved in water, it combines with water and forms a new substance called magnesium hydroxide.
3. What type of change is the burning of coal?
Ans: Burning of coal is a chemical change.
C. Short Answer Type-I Questions:
1. What is meant by rusting of iron?
Ans: Rusting of iron is a chemical change that happens when the iron is kept in contact with moist air. During this change, hydrated iron oxide or rust is formed that damages the objects made of iron.
2. State any two conditions necessary for the rusting of iron.
Ans: The presence of oxygen and moisture in the air is necessary for the rusting of iron.
3. Why is the melting of ice to form water considered a physical change?
Ans: Melting of ice to form water is considered a physical change because no new substance is formed during this change, and it is a temporary change.
D. Short Answer type-II Questions:
1. What are the characteristic of physical changes?
Ans: The characteristic of physical changes are as follows:
Generally, a physical change is reversible and no new substance is formed. The chemical composition of the substance remains the same after a physical change. Only some of the physical properties such as size, shape, color, and state change during a physical change.
2. What are the characteristic of chemical changes?
Ans: The characteristic of chemical change are as follows,
Chemical changes are generally permanent, and one or more new substances are formed. During a chemical change, both the physical and chemical properties of a substance are changed. A large amount of energy is either given out or absorbed in the form of heat or light during a chemical change.
3. Why is explosion of crackers considered a chemical changes?
Ans: The explosion of crackers is considered a chemical change because during this change, new substances are formed, and energy is released in the form of heat, light, and sound.
4. Does the change in chemical properties take place during a chemical change?
Ans: Yes, the change in chemical properties takes place during a chemical change, for eg, when hydrogen reacts with oxygen, it forms water, and the chemical properties of hydrogen, oxygen, and water are very different.
5. Ram and Raheem are best friends. Raheem goes to Ram’s house to celebrate Diwali. Both are burning crackers. Suddenly, a park falls on Raheem’s arm. Ram immediately washes Raheem’s hand and applies a cream for burns.
(a) Which type of change is the burning of crackers?
Ans: The burning of crackers is a chemical change.
(b) Do you think, burning crackers is good for our environment?
Ans: I think burning crackers is very harmful to our environment because the gases produced while burning it pollutes the environment and harms trees and animals.
(c) Which value is shown by Ram here?
Ans: Ram’s action shows value of compassion and kindness.
E. Long Answer Questions:
1. Write the differences between physical and chemical changes.
2. Describe, how crystals of copper sulphate are prepared.