Q3 .Name the following :
a. The product formed when magnesium burns in oxygen.
Answer. Magnesium oxide (MgO) is the product formed when magnesium burns in oxygen.
- The table which shows the arrangement of metals on the basis of their ability to react .
Answer. A reactivity series is a list of metals arranged in order of their reactivity. This series helps us understand how readily metals react with other substances, such as oxygen, water, and acids.
c.A change in which no new substance is formed
Answer. A physical change is a change in which no new substance is formed.
d.The original substance that takes part in a chemical in a chemical reaction.
Answer. Reactants are the original substances that take part in a chemical reaction.
Q4. Answer the following questions in one sentence.
a. How is the setting of curd a chemical change ?
b. How does painting prevent the rusting of an iron object?
c. What is a chemical change?
d. What is an alloy?
Q5. Answer the following questions in 3-4 sentences.
a.Explain why the water cycle is an example of reversible changes.
b.Explain what happens when iron nails are dipped in copper sulphate solution?
c. When iron filings are mixed with sulphur powder a mixture is formed which is physical changewhile chemical change occurs when the same mixture is heated .justify
d.What is an irreversible physical change ?explain with help of an example
Q1. Answer the following questions in one sentence.
a. How is the setting of curd a chemical change?
- The setting of curd is a chemical change because it involves the conversion of milk proteins into solid curd, which is a new substance with different properties.
b. How does painting prevent the rusting of an iron object?
- Painting prevents the rusting of an iron object by creating a protective barrier that isolates the iron from oxygen and moisture, which are the main factors that cause rust.
c. What is a chemical change?
- A chemical change is a process in which one or more substances are transformed into new substances with different properties.
d. What is an alloy?
- An alloy is a mixture of two or more metals, or a metal and a nonmetal, that has properties different from those of its individual components.
Q2. Answer the following questions in 3-4 sentences.
a. Explain why the water cycle is an example of reversible changes.
- The water cycle is an example of reversible changes because it involves the transformation of water between its three states: solid, liquid, and gas. These changes can be reversed under different conditions. For example, water can evaporate from a liquid to a gas, condense from a gas to a liquid, and freeze from a liquid to a solid.
b. Explain what happens when iron nails are dipped in copper sulphate solution.
- When iron nails are dipped in copper sulphate solution, a chemical reaction occurs. The iron reacts with the copper ions in the solution, displacing the copper from the solution and forming iron sulphate. The copper is deposited onto the iron nails, giving them a reddish-brown color.
c. When iron filings are mixed with sulphur powder a mixture is formed which is a physical change while chemical change occurs when the same mixture is heated. Justify.
- When iron filings are mixed with sulphur powder, a mixture is formed. This is a physical change because the individual components (iron and sulphur) retain their original properties and can be separated by mechanical means. However, when this mixture is heated, a chemical reaction occurs, forming iron sulphide, a new substance with different properties. This is a chemical change.
d. What is an irreversible physical change? Explain with the help of an example.
- An irreversible physical change is a change that cannot be reversed. Once the change has occurred, it is not possible to return the substance to its original state. An example of an irreversible physical change is burning a piece of paper. Once the paper is burned, it cannot be returned to its original state as a whole piece of paper.