Uses, Minerals, and What Is Not Matter — "Nature of Matter: Elements, Compounds, and Mixtures"

1. 14 marksCuriosity Grade 8, Chapter 8, pages 128-129

   Give examples from section 8.4 of how understanding elements, compounds and mixtures leads to innovation.

   Hint. The chapter names three professions and what each does with the idea.

   All around us, first. The air we breathe is a mixture of gases like oxygen, nitrogen, and carbon dioxide. Water, which is essential for life, is a compound made of elements, hydrogen and oxygen. Elements like iron and aluminium are used to construct bridges, buildings, and vehicles.

   Then the innovation, by profession:

   Who	What they do with it
   Chemists	Study how elements combine to create compounds, enabling them to invent life-saving medicines and vaccines to fight diseases
   Chemists, again	Create fertilisers, thereby enhancing crop production that feeds the ever-increasing human population globally
   Engineers and material scientists	Design materials with unique properties ... alloys like stainless steel, which is stronger and more durable than pure iron

   ✦ The chapter's own conclusion: Understanding these concepts is not just about recognising what surrounds us; it is also the key to innovation. Classification is not the end of the work. Once you know that properties come from how elements are combined, you can start choosing the combination to get the properties you want.

   And a reminder that mixtures are not second-class: Wood, steel, and concrete, which are used as building materials, are all mixtures. Nearly everything a city is built from is a mixture, chosen because mixing gives properties no pure substance offers.

2. 23 marksCuriosity Grade 8, Chapter 8, page 129

   What is graphene aerogel? Why does its structure give it the uses the chapter describes?

   Hint. Follow the chain from what it is made of, to a property, to a use.

   An example of a 'wonder' material developed by material scientists is graphene aerogel. This is made from carbon and is said to be the lightest material on earth. It is so light that even grass can hold it. It is highly porous and therefore, has a high absorbing capacity. For this reason, it can potentially be used as an environmental cleaner, for example, to clean up oil spills in both seas and on land. It is useful in fabricating energy-saving devices and special coatings for buildings.

   The chain of reasoning, which is the answer:

   Made from carbon → arranged into a highly porous structure → almost all of it is empty space, so it is extremely light and has an enormous internal surface → therefore a high absorbing capacity → therefore useful for soaking up oil spills.

   ✦ Notice that it is made from carbon — an element you have already met in this chapter as the charcoal left behind when sugar is heated. Same element, utterly different material, because the structure is different. That is a large idea in disguise: properties depend not only on which elements are present but on how they are arranged.

   The word potentially is the chapter's, and it should be yours. The material exists and the property is real; the large-scale clean-up use is a possibility being worked on, not something already routine.

3. 34 marksCuriosity Grade 8, Chapter 8, page 129

   What are minerals? What are native minerals, and how do most minerals differ from them?

   Hint. Most rocks are mixtures; the minerals in them usually are not.

   Most rocks are a mixture of minerals, which can be viewed with the eyes, or by using a magnifying glass or a microscope. Some of the minerals are called native minerals, which are pure elements and not compounds. These can be metals, such as gold, silver, copper, etc., or non-metals like sulfur, carbon, etc.

   Most of the minerals are compounds made up of more than one element. Some common examples of minerals include quartz, calcite, mica, pyroxene, and olivine.

   And the Snapshot's definition: Minerals are natural, solid substances found on the Earth. They have a fixed chemical composition. Most often they are compounds but rarely, they can also be pure elements.

   	Native minerals	Most minerals
   What they are	Pure elements	Compounds of more than one element
   Examples	Gold, silver, copper; sulfur, carbon	Quartz, calcite, mica, pyroxene, olivine
   How common	Rare	The usual case

   ✦ Three levels are stacked here and questions often test the stacking. A rock is a mixture; the minerals in it are pure substances; and each mineral is either a compound or, occasionally, an element. So the same lump of stone is a mixture, a set of compounds and a set of elements depending on how closely you look.

   Two everyday products the chapter traces back: cement is made from calcite, quartz, alumina, and iron oxide, and talcum powder is made from the mineral talc.

4. 43 marksCuriosity Grade 8, Chapter 8, page 130

   Which of these are not matter — light, heat, a stone, electricity, air, a thought? Give the chapter's reason.

   Hint. The definition of matter has two parts, and both must hold.

   	Matter?	Why
   Light	No	Has no mass and occupies no space
   Heat	No	A form of energy, not a substance
   A stone	Yes	Has mass and takes up space
   Electricity	No	Named by the chapter as not matter
   Air	Yes	Has mass and occupies space, though invisible
   A thought	No	The chapter names thoughts and emotions explicitly

   Elements and compounds are the building blocks of matter — everything that has mass and takes up space. They make the materials we see and use every day. However, not everything around us is matter. Light, heat, electricity, and even thoughts and emotions are important parts of our world, but they are not made of matter.

   ✦ Note the phrase important parts of our world. The chapter is not saying these things are unreal or unimportant — it is saying they are not made of matter, which is a statement about what they are, not about whether they count. And that is the last line of the section: Understanding what matter is — and what it is not — helps us better understand the world around us.

   Air is the pair to light here. Invisible but matter; visible but not matter. Between them they show that visibility has nothing to do with the test.

5. 54 marksCuriosity Grade 8, Chapter 8, page 130

   Describe the Dhokra art process and identify the elements, compounds and mixtures in it.

   Hint. Follow the process step by step, then classify each material it uses.

   The process.

   The Dhokra art is an old craft from Bihar and Odisha that uses different metals to create beautiful figures inspired by nature. The process begins with shaping a design in beeswax. This wax model is covered with clay to make a mould. After the clay hardens, the wax is melted out, leaving a hollow space. This space is then filled with molten brass or bronze which makes Dhokra art strong and gives it a shiny golden colour. The figures often show animals, people, and nature, reflecting tribal creativity and tradition.

   Classifying the materials:

   Material	Category
   Beeswax	Mixture — a natural material of several substances
   Clay	Mixture — minerals, water and other matter
   Brass	Mixture — an alloy of copper and zinc
   Bronze	Mixture — an alloy of copper and tin
   Copper, zinc, tin	Elements

   ✦ The craft depends on properties this chapter explains. Wax has a low melting point, so it can be melted out of a mould that clay — with a far higher one — easily survives. Brass and bronze are alloys, chosen because mixing gives a metal that is strong and pours well and takes a golden colour. Every choice in the process is a choice about material properties, made long before anyone wrote the word 'alloy'.

   Note the link back to page 118. Bronze here is the same Kamsya of the Mishraloha box — copper and tin — showing up in an entirely different tradition and use.

6. 63 marksCuriosity Grade 8, Chapter 8, pages 128-129

   Wood, steel and concrete are all mixtures. Why would a builder prefer mixtures to pure substances?

   Hint. Compare stainless steel with pure iron, using the chapter's own comparison.

   Because mixing lets you choose the properties you need. The chapter's example is exact: they have developed alloys like stainless steel, which is stronger and more durable than pure iron. Pure iron is neither as strong nor as resistant to rusting; adding nickel, chromium and a little carbon gives a material that is both.

   Three reasons, all of them practical:

   1. Properties can be tuned. A mixture's proportions can be varied, so a steel can be made harder or more flexible as the job demands. A compound's fixed ratio offers no such choice.
   2. Weaknesses can be compensated. Concrete resists being squashed but not stretched, so steel rods are set inside it — a mixture at the scale of a building.
   3. Cost and availability. Purifying a substance completely is expensive, and there is rarely any reason to pay for it if a mixture performs better anyway.

   ✦ This inverts the everyday sense of 'pure'. In common usage pure means better; in materials science, pure iron is the inferior building material and no one would use it for a bridge. Purity is a description of composition, not a measure of quality — which is exactly the distinction section 8.2 drew, arriving here from the other direction.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 8 (hecu108.pdf), Reprint 2026-27, pages 116-133. Questions are referenced from the NCERT textbook for identification.