RBSE Solutions Class 7 Science Chapter 4 The World of Metals and Non metals

Class 7 Science Curiosity Chapter 4 Question Answer (Exercise)

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Question 1. Which metal is commonly used to make food packaging materials as it is cheaper, and its thin sheets can be folded easily into any shape?
(i) Aluminium
(ii) Copper
Answer: (i) Aluminium
In simple words: Aluminium is widely used for food packaging because it is inexpensive and can be easily shaped into thin sheets. This makes it perfect for wrapping and protecting food.

🎯 Exam Tip: Remember that aluminium is known for its malleability (can be hammered into thin sheets) and ductility (can be drawn into wires), which are key properties for its use in packaging and other applications.

Question 2. Which of the following metal catches fire when it comes in contact with water?
(i) Copper
(ii) Aluminium
(iii) Zinc
(iv) Sodium
Answer: (iv) Sodium
In simple words: Sodium is a very reactive metal that can easily catch fire when it touches water. This is why it must be stored very carefully, usually under oil.

🎯 Exam Tip: Recall the reactivity series of metals; alkali metals like sodium and potassium are highly reactive and react vigorously with water, often producing heat and hydrogen gas which can ignite.

Question 3. State with reason(s) whether the following statements are True [T] or False [F].
(i) Aluminium and copper are examples of non-metals used for making utensils and statues.
Answer: False (F), because aluminium and copper are metals, and they have characteristics of metals like malleability, ductility and conduction.
In simple words: Aluminium and copper are metals, not non-metals. They can be shaped and stretched, and they conduct heat and electricity well, which are all traits of metals.
(ii) Metals form oxides when combined with oxygen, the solution of which turns blue litmus paper to red.
Answer: False (F), because the oxides of metals are of basic nature and their solution does not change colour of blue litmus even they turn red litmus into blue.
In simple words: Metal oxides are basic, which means they turn red litmus paper blue, not the other way around. Blue litmus paper stays blue with basic solutions.
(iii) Oxygen is a non-metal essential for respiration.
Answer: True (T), because oxygen is a non-metal and essential for respiration in living organisms.
In simple words: Oxygen is indeed a non-metal and is vital for all living things to breathe and get energy. Without it, life as we know it would not exist.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity.
Answer: False (F), because copper vessels are used for boiling water but not because they are good conductors of electricity but they are good conductors of heat, heat is important here.
In simple words: Copper pots are good for boiling water because copper is excellent at conducting heat, not electricity. Good heat conduction helps water boil quickly.

🎯 Exam Tip: When answering True/False questions with reasons, always state whether it's true or false first, then provide a clear, concise, and accurate scientific explanation for your choice. Make sure to distinguish between heat and electrical conductivity.

Question 4. Why are only a few metals suitable for making jewellery?
Answer: Only a few metals are suitable for making jewellery because they need to have special properties. These metals must be shiny, look attractive, resist corrosion (not rust or tarnish easily), and be very malleable (easy to shape) and ductile (can be drawn into thin wires). Gold, silver, and platinum are examples of such metals that meet these criteria perfectly. Their unreactive nature helps them keep their shine over a long time.
In simple words: Only certain metals like gold and silver are good for jewellery because they are shiny, don't rust, and are easy to shape into beautiful designs.

🎯 Exam Tip: Key terms to include when explaining jewellery metals are "lustrous" (shiny), "malleable," "ductile," and "corrosion-resistant" or "unreactive."

Match the Uses of Metals and Non-Metals Given in Column I with the Jumbled Names of Metals and Non-Metals Given in Column II. Column-I

Answer:

🎯 Exam Tip: For matching questions, first identify the key property or use in Column I and then look for the jumbled name in Column II that fits, unscrambling it as needed. Always try to unscramble the names to verify your match.

Question 6. What happens when oxygen reacts with magnesium and sulfur? What are the main differences in the nature of products formed?
Answer: When oxygen reacts with magnesium, it forms magnesium oxide. Magnesium oxide is a metal oxide, which means it is basic in nature. If dissolved in water, it turns red litmus paper blue. This happens because magnesium is a metal. On the other hand, when oxygen reacts with sulfur, it forms sulfur dioxide. Sulfur dioxide is a non-metal oxide, which means it is acidic in nature. If dissolved in water, it turns blue litmus paper red. This reaction shows how metals and non-metals behave differently with oxygen, producing oxides with opposite chemical properties.
In simple words: Oxygen reacting with magnesium makes a basic substance, magnesium oxide. Oxygen reacting with sulfur makes an acidic substance, sulfur dioxide. The main difference is that one is basic and the other is acidic.

🎯 Exam Tip: Remember that oxides of metals are generally basic, while oxides of non-metals are generally acidic. This is a fundamental concept in chemistry often tested with litmus paper examples.

Question 7. Complete the following flow chart:
Answer: The flowchart shows the reaction of magnesium (Mg) with air (oxygen) and heat, producing ash (magnesium oxide). This ash, when mixed with water, forms a solution that is tested with litmus paper.
The completed flowchart steps are:
1. Magnesium (Mg) + Air (Oxygen) + Heat \( \implies \) Ash (Magnesium Oxide)
2. Ash (Magnesium Oxide) + Water \( \implies \) Solution (Magnesium Hydroxide)
3. When this solution is added to blue litmus solution, there is No Change.
4. When this solution is added to red litmus solution, it turns Blue.
This shows that magnesium oxide, a metal oxide, forms a basic solution when dissolved in water.
In simple words: Magnesium burns in air to make ash, which is magnesium oxide. When this ash mixes with water, it makes a basic solution. This solution does not change blue litmus paper, but it turns red litmus paper blue.

🎯 Exam Tip: Understanding the basic nature of metal oxides is crucial. Remember that basic solutions do not affect blue litmus paper but change red litmus paper to blue.

Question 8. You are provided with the following materials. Discuss which material would be your choice to make a pan that is most suitable for boiling water and why?
Answer: Among the mentioned materials (implicitly, iron and copper based on the next page's context), iron and copper are the most suitable choices for making a pan to boil water. This is because both iron and copper are metals that are excellent conductors of heat and are solid. Good heat conduction means that heat from the stove will quickly transfer to the water, allowing it to boil efficiently. Other materials, if they are brittle or poor conductors of heat, would not be suitable for making a cooking pan. The ability to conduct heat well is the primary reason for choosing these metals.
In simple words: To make a pan for boiling water, iron and copper are the best choices. They are good at letting heat pass through, so water boils quickly.

🎯 Exam Tip: When choosing materials for cooking utensils, prioritize properties like high thermal conductivity (to transfer heat efficiently), durability (to withstand heat and use), and non-reactivity with food items.

Question 9. You are provided with three iron nails, each dipped in oil, water and vinegar. Which iron nail will not rust, and why?
Answer: The iron nail dipped in oil will not rust. Rusting happens when iron comes into contact with both air (oxygen) and water. The layer of oil completely covers the nail, creating a barrier that stops air and water from touching its surface. Because the nail does not come into direct contact with either air or water, the conditions necessary for rusting are prevented, and thus, the nail remains free from rust. Oil acts as a protective shield.
In simple words: The iron nail in oil will not rust. The oil layer stops air and water from reaching the nail, which are both needed for rust to form.

🎯 Exam Tip: Remember that both oxygen and water are essential for iron to rust. Methods of rust prevention often involve creating a barrier to keep one or both away from the iron surface.

Question 10. How do the different properties of metals and non-metals determine their uses in everyday life?
Answer: The unique properties of metals and non-metals decide how we use them every day:
**Properties of Metals:**
* **Malleability:** Metals can be beaten into thin sheets. This is why aluminium foil is used for wrapping food, and copper, silver, gold, and other metals are shaped into utensils and ornaments. Their ability to be shaped without breaking makes them versatile.
* **Ductility:** Metals can be pulled into thin wires. Gold and silver are used to make fine jewellery, and copper is used for electrical wiring. This allows them to be used for intricate designs and conductive paths.
* **Conduction:** Metals are excellent conductors of heat and electricity. This property makes them useful for making cooking utensils (like pots and pans) and electrical tools and wires. They allow energy to flow through them easily.
* **Sonority:** Metals make a ringing sound when struck. This is why metals are used in temple bells and wires in musical instruments. Their ability to produce clear sounds is valued in acoustics.
**Characteristics of Non-Metals and their Uses in Daily Life:**
* **Conductivity:** Non-metals are generally poor conductors of heat and electricity. This is why handles of cooking utensils and electric tools are often made from materials like plastic and rubber, which act as insulators and protect us from heat and electric shock.
* **Brittle:** Non-metals are often brittle and break easily. They are used in powdered form for things like fertilizers and medicines. Phosphorus is used in matchsticks, and graphite (a form of carbon) is used in pencils because of its soft and layered structure.
* **Gaseous:** Many non-metals are gases at room temperature. For example, oxygen is a life-giving non-metal vital for breathing, and nitrogen is essential for plant growth. Their gaseous state allows them to be part of the air we breathe and the cycles of life.
* **Other:** Carbon forms the basic building blocks of all life forms. Chlorine is used as a water purifier to kill germs, and iodine solution is an antiseptic to clean wounds. These diverse uses highlight their importance across various applications.
In simple words: Metals are used for things like wires, cooking pots, and jewellery because they are shiny, can be shaped, and conduct heat and electricity. Non-metals are used for things like insulators, fertilizers, medicines, and even for breathing (like oxygen) because they have different properties, like being brittle or being gases.

🎯 Exam Tip: When describing properties and uses, group them logically (e.g., all metal properties together, then all non-metal properties). Provide specific examples for each property to illustrate its real-world application clearly.

Question 12. An ironsmith heats iron before making tools. Why is heating necessary in this process?
Answer: An ironsmith heats iron before making tools because heating significantly improves the malleability and ductility of iron. When iron is heated to a high temperature, it becomes softer and more flexible. This makes it much easier for the ironsmith to hammer, bend, and shape the iron into the desired tools and utensils without the metal cracking or breaking. The heat allows the iron atoms to move more freely, making the material less brittle and more workable.
In simple words: Heating iron makes it softer and easier to shape. This allows the ironsmith to hammer and bend it into tools without it breaking.

🎯 Exam Tip: Focus on the properties of malleability and ductility when explaining why metals are heated for shaping. Explain how heat makes metals less brittle and more workable.

The World of Metals and Non Metals Class 7 Questions and Answers (Intext)

Page No. 43

Question 1. Are all metals hard and solid?
Answer: No, not all metals are hard and solid. While most metals are hard and exist in a solid state at room temperature, there are exceptions. Metals like sodium and potassium are so soft that they can easily be cut with a knife. Additionally, mercury is a metal that is found in a liquid state at room temperature. These exceptions show that metal properties can vary.
In simple words: No, not all metals are hard and solid. Some, like sodium, are soft enough to cut with a knife, and mercury is a liquid at normal temperatures.

🎯 Exam Tip: Always remember the common exceptions to general rules about metals, such as mercury (liquid metal) and sodium/potassium (soft metals), as these are frequently asked.

Question 2. Which objects become flat on beating with a hammer?
Answer: Objects that are malleable will become flat when beaten with a hammer. Metals are typically malleable. For example, a piece of copper, a piece of aluminium, and an iron nail are all made of metal, so they will flatten when struck with a hammer. This property allows metals to be shaped into various forms without breaking.
In simple words: Objects made of metal, like copper, aluminium, or an iron nail, will flatten when hit with a hammer because they are malleable.

🎯 Exam Tip: Connect the observation of flattening with the scientific property of "malleability," which describes a material's ability to be hammered or pressed into thin sheets without breaking.

Page No. 44

Question 3. Where do you find the use of metal wires?
Answer: Metal wires are used in many places. You can find wires made of metals like copper or aluminium in electrical fittings in our homes and buildings. They carry electricity safely. In ornaments, such as bangles, necklaces, and earrings, metal wires are crucial for their design and structure. Furthermore, metal wires are essential in various stringed musical instruments like the Veena, Sitar, Violin, and Guitar, where they produce sound when vibrated. Their ability to be drawn into thin threads makes them incredibly useful.
In simple words: Metal wires are used in electrical connections, for making jewellery like necklaces, and in musical instruments that have strings.

🎯 Exam Tip: When listing uses, provide diverse examples that highlight different properties of metals, such as electrical conductivity for wiring and ductility for jewellery and musical strings.

Page No. 45

We observed that a spoon and the metal coin produce a ringing sound which is called sonority. Coal and wood on the other hand, produce a dull sound.

Page No. 46

Question 5. Can you name some metal that are used for making cooking vessels? Do you know why these metals are used for this purpose?
Answer: Metals like iron, steel, aluminium, copper, and brass are commonly used for making cooking vessels. These metals are chosen for this purpose primarily because they are excellent conductors of heat. Being good conductors, they efficiently transfer heat from the stove to the food, allowing it to cook thoroughly and quickly. This property ensures even cooking and saves energy. Their durability and ability to withstand high temperatures also make them suitable for cookware.
In simple words: Iron, steel, aluminium, copper, and brass are used for cooking pots. They are good at conducting heat, which helps food cook well and fast.

🎯 Exam Tip: When discussing cooking vessels, emphasize the property of "thermal conductivity" (good conductor of heat) as the main reason for using metals, as it directly impacts cooking efficiency.

Question 6. Have you ever seen an electrician using screw driver? What type of material is used for making its handle? You may have also noticed the electrician wearing rubber gloves and shoes while working. What can be the reason for this?
Answer: Yes, electricians use screwdrivers regularly. The handle of a screwdriver is typically made from plastic or rubber. The reason for this, and for electricians wearing rubber gloves and shoes while working with electricity, is that both plastic and rubber are excellent electrical insulators. Insulators do not allow electricity to pass through them easily. Therefore, these materials protect the electrician from electric shock by preventing direct contact with live electrical currents, ensuring their safety during work. This is a critical safety measure when handling electrical circuits.
In simple words: Screwdriver handles are made of plastic or rubber. Electricians wear rubber gloves and shoes because plastic and rubber stop electricity from flowing, keeping the electrician safe from shocks.

🎯 Exam Tip: Distinguish between conductors (materials that allow electricity to pass) and insulators (materials that block electricity). Provide practical examples of how insulators are used for safety around electrical appliances.

Page No. 48

Question 7. In which conditions would an iron object develop brown deposits?
• When it comes into contact with dry air only.
• When it comes into contact with water only.
• When it comes into contact with both air and water.
Answer: When it comes into contact with both air and water.
In simple words: An iron object will get brown deposits (rust) only when it touches both air (oxygen) and water at the same time.

🎯 Exam Tip: Remember the two necessary conditions for rusting: presence of oxygen (from air) and moisture (water). If either is absent, rusting will not occur or will be significantly slowed down.