Textbook Solutions: Changes Around Us | Eureka Plus Class 6: Book Solutions, Notes & Worksheets PDF Download

I. Answer the following questions in one sentence. 

II. Answer the following questions in two to three sentences. 

1.
Ans: Reversible changes are those that can be changed back to their original form, and they are typically physical changes. For example, water freezing into ice and then melting back into water is a reversible change. Irreversible changes, on the other hand, involve the formation of new substances with different properties, and they are mostly chemical changes. For instance, when sugar is heated and turns into carbon, it's an irreversible change.

2.
Ans: To prevent an iron sheet from rusting, you can apply oil paint on it. This forms a protective barrier, preventing contact between the iron and moisture, which causes rust.

3.
Ans: The formation of a salt solution is a physical change because both the salt and water retain their properties, and they can be separated by the process of evaporation. The individual components of the mixture remain unchanged.

4.
Ans: Burning of sugar is a chemical change because it results in the formation of a new substance, which is carbon. The properties of the burnt sugar are different from those of sugar. The change is irreversible, and it involves a chemical reaction.

5.
Ans: You can change matter from its liquid state to its solid state by reducing the temperature. For example, when you freeze water, it changes from a liquid state to a solid state and becomes ice.

III. Read the passage and answer the questions

1.
Ans: The four distinct changes mentioned in the passage are:

• Bees collecting nectar and changing it into honey.
• Bees transferring pollen grains from one flower to another.
• The transformation of flowers into fruits with seeds inside.
• Seeds growing into new plants.

2.
Ans: Yes, all these changes are natural processes that occur in the natural world.

3.
Ans: Among these changes, the transformation of nectar into honey by bees is a reversible change because honey can change back into nectar. The transfer of pollen grains is a natural process and can be considered relatively fast.

4.
Ans: Yes, nectar and honey have different properties. Nectar is a watery, colorless, transparent liquid with a sweet taste, while honey is a thick, opaque liquid with a brownish color and a sweet taste. The two substances differ in their physical characteristics.

IV. Answer the following questions in five to six sentences. 

1.
Ans: In my surroundings, I observe various changes:

• The transition from night to day, where darkness changes into daylight, and the sun rises.
• The growth of plants from seeds, where tiny seeds sprout and develop into mature plants.
• Cooking food, which involves the transformation of raw ingredients into a cooked and edible form, a desirable change.
• The changing seasons, such as the transition from summer to fall, which affects the weather and the environment around us.

2.
Ans: 

• Desirable changes are those that are beneficial or useful, such as the ripening of fruits, the germination of seeds, and the formation of honey by bees. These changes have positive effects and are often essential for our well-being.
• Undesirable changes, on the other hand, are harmful or not beneficial. Examples include the rotting of fruits, the rusting of iron, and the actions of disease-causing microorganisms in the human body. Undesirable changes can lead to negative consequences, such as spoilage or illness.

3.
Ans:

• A chemical change is a change in which new substances with different properties are formed. It involves the breaking and forming of chemical bonds. For example, when sugar is heated and turns into carbon, it's a chemical change.
• A physical change, on the other hand, is a change that affects only the physical properties of a substance without forming new substances. These changes are typically reversible. For instance, when water freezes into ice, it's a physical change because it remains water in a different state. Changes in shape, size, or state of matter without altering the chemical composition are physical changes.

4.
Ans: Changes involve energy in various forms. For example, when wood burns, it undergoes a chemical change and produces heat and light energy. This energy is released in the form of heat and light during the combustion process. Energy is also required for changes to occur, like the solar energy from the morning sunlight that causes sunflower buds to bloom. In all these cases, energy is a crucial factor in driving and accompanying changes in the natural world.

Think and answer

I. 
1.
Ans: The compositions of the two mixtures are:

• Mixture 1: Sodium hydroxide (solid) and hydrochloric acid (liquid).
• Mixture 2: Table salt and water.

2.
Ans: The first mixture, consisting of sodium hydroxide and hydrochloric acid, reacts and forms two different substances, which are table salt and water.

3.
Ans: Mixing salt and water is a physical change because it does not alter the chemical composition of salt or water. The salt remains as salt, and the water remains as water. It is a change in the state of matter but not in the chemical identity of the substances.

4.
Ans: The mixture of sodium hydroxide and hydrochloric acid brings about a chemical change because it results in the formation of new substances (table salt and water) with different properties. Chemical bonds are broken and formed during this reaction, leading to a change in the chemical composition of the substances involved.

II. Read the sentence and answer the questions that follow.
A large lump of sea salt was ground and changed into powder.
1.
Ans:  Yes, powdered sea salt will dissolve in water. The size of the salt particles has been reduced, but it is still the same substance, and it retains its ability to dissolve in water.

2.
Ans: Yes, the powdered sea salt will have the same taste as the lump of sea salt. The taste of salt is a characteristic of its chemical composition, which remains unchanged in the process of grinding it into powder.

3.
Ans: No, the lump of sea salt and the powdered sea salt are not different substances. They are both composed of the same chemical compound, sodium chloride. The only difference lies in their physical form, with one being a solid lump and the other being a powdered form.

4.
Ans: Making salt powder is a physical change because it involves changing the physical state of the substance without altering its chemical composition. The chemical identity of salt remains the same; only the size and physical form of the salt particles are changed.