An Overview of Class 8 Science Materials Metals And Non Metals Worksheets
FAQs on Class 8 Science Materials Metals And Non Metals Worksheets
1. What are some important uses of metals and non-metals that are frequently asked in Class 8 exams for the session 2025-26?
For your Class 8 exams, it's important to know specific uses of metals and non-metals as outlined in the NCERT syllabus. Key examples include:
- Metals: Iron is used for making machinery and bridges due to its strength. Copper is used for electrical wires because it is a good conductor of electricity. Aluminium is used for making utensils and foils due to its malleability and resistance to corrosion. Gold and silver are used for jewellery due to their lustre and non-reactive nature.
- Non-metals: Oxygen is essential for respiration. Nitrogen is used in fertilisers to promote plant growth. Chlorine is used for water purification. Iodine is used as an antiseptic (tincture of iodine).
2. For a 3-mark question, state three key differences between the physical properties of metals and non-metals with examples.
To secure full marks, you should present the differences in a clear format. Here are three important distinctions:
- Malleability and Ductility: Metals are generally malleable (can be beaten into thin sheets) and ductile (can be drawn into wires), like aluminium and copper. Non-metals are brittle and break when hammered; for example, sulphur or carbon.
- Conductivity: Metals are good conductors of heat and electricity. For instance, iron conducts heat and copper conducts electricity. Non-metals are typically poor conductors, with graphite (a form of carbon) being a notable exception.
- Lustre: Metals have a shiny surface, a property known as lustre (e.g., gold, silver). Non-metals usually have a dull appearance (e.g., phosphorus), with iodine being an exception.
3. Why is sodium metal stored under kerosene? Why is this considered an important conceptual question?
This is an important question because it tests your understanding of the reactivity series. Sodium is a highly reactive metal. It reacts vigorously and exothermically (releases a lot of heat) with both oxygen and moisture present in the air. This reaction can be so intense that it catches fire. To prevent this, sodium is stored in kerosene, as kerosene is an inert liquid that prevents the metal from coming into contact with air and water. This concept is fundamental to understanding the varying reactivity of different metals.
4. Explain with an example why a more reactive metal displaces a less reactive metal from its salt solution. What is a 2-mark question that can be asked on this concept?
A more reactive metal displaces a less reactive one because it has a stronger tendency to lose electrons and form ions. When a more reactive metal like zinc is placed in a solution of a less reactive metal salt like copper sulphate, the zinc displaces the copper.
Reaction: Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s).
The blue colour of the copper sulphate solution fades and a red-brown deposit of copper forms. A typical 2-mark question would be: 'What do you observe when an iron nail is placed in a copper sulphate solution? Write the chemical equation for the reaction.'
5. Why can't we use a spoon made of aluminium to stir a zinc sulphate solution? Explain the chemical principle involved, which is a Higher Order Thinking Skills (HOTS) question.
You cannot use an aluminium spoon to stir a zinc sulphate solution. The reason lies in the reactivity series. Aluminium is more reactive than zinc. According to the displacement rule, a more reactive metal displaces a less reactive metal from its salt solution. Therefore, if an aluminium spoon is used, the aluminium will react with and displace the zinc from the zinc sulphate solution, causing the spoon to corrode and contaminating the solution. The spoon will gradually dissolve, forming aluminium sulphate.
6. Most non-metals are poor conductors of electricity. Name a non-metal that is an exception and explain why this property is important for its uses. This is a frequently asked question.
The exception is graphite, which is an allotrope (a specific form) of the non-metal carbon. Graphite can conduct electricity because of its unique layered structure where electrons are free to move between the layers. This property makes it very useful. It is used to make electrodes in batteries and industrial electrolysis processes, which are applications where electrical conductivity is essential.
7. Compare the reaction of metals and non-metals with oxygen. How do their oxides differ in nature? This is a potential 5-mark question.
This is a crucial comparison for your exams. Here's how they differ:
- Metals with Oxygen: Metals react with oxygen to form metal oxides, which are generally basic in nature. For example, when magnesium burns in air, it forms magnesium oxide (MgO). When this oxide is dissolved in water, it forms magnesium hydroxide, a base, which turns red litmus paper blue.
- Non-metals with Oxygen: Non-metals react with oxygen to form non-metal oxides. These oxides are typically acidic in nature. For instance, when sulphur burns in air, it forms sulphur dioxide (SO₂). When dissolved in water, it forms sulphurous acid, which turns blue litmus paper red.
The key takeaway is that metal oxides are basic, while non-metal oxides are acidic.
8. Why are school bells and musical instrument strings made of metals and not wood or plastic? Which important property of metals is demonstrated here?
School bells and musical instrument strings are made of metals because of a special property called sonority. Metals are sonorous, which means they produce a deep, ringing sound when struck. Wood and plastic do not have this property; they produce a dull sound. This ability to resonate and produce a sustained sound is why metals like brass or steel are chosen for making bells and strings for instruments like guitars and violins.
9. Explain the phenomenon of rusting on iron and the formation of a greenish deposit on copper. What is the important takeaway for your exams from these two corrosion examples?
Both are important examples of corrosion.
- Rusting of Iron: When iron is exposed to both oxygen and moisture (water), it undergoes a chemical reaction to form hydrated iron(III) oxide, commonly known as rust. Rust is flaky and porous, which gradually destroys the iron object.
- Corrosion of Copper: When copper objects are exposed to moist air for a long time, they acquire a dull green coating. This coating is a mixture of copper hydroxide [Cu(OH)₂] and copper carbonate [CuCO₃], formed by the reaction of copper with water, carbon dioxide, and oxygen in the air.
The important takeaway is that corrosion damages metals, and the conditions required for corrosion can differ. For iron, it's oxygen and water; for copper, it also involves carbon dioxide from the air.
