What Are Mixtures? — Components, Uniform and Non-uniform — "Nature of Matter: Elements, Compounds, and Mixtures"

1. 13 marksCuriosity Grade 8, Chapter 8, page 117

   Define a mixture and its components, and state the one condition the chapter attaches to the definition.

   Hint. The condition is about what the substances must *not* do to each other.

   When two or more substances are mixed, where each substance retains its properties, it is called a mixture. The individual substances that make up a mixture are called its components.

   The components of a mixture do not react chemically with each other.

   ✦ That last line is the whole definition, not an extra detail. If the substances react, what you have afterwards is a new substance with new properties — a compound — and the originals are gone. In a mixture nothing is gone: the sugar in sugar water is still sugar and still tastes sweet, and the iron in Sample A of Activity 8.5 is still magnetic.

   A useful way to test yourself: can I still find the original substances in there, behaving as they always did? If yes, it is a mixture, because nothing has been chemically changed. In Activity 8.5 you can answer that question with a magnet.

2. 23 marksCuriosity Grade 8, Chapter 8, pages 117-118

   What is a non-uniform mixture? Give the chapter's example and two of your own.

   Hint. The defining word is whether the components can be *distinguished*.

   In some mixtures, the components — like green gram, chickpeas, onion, and tomato in a sprout salad, are easy to see. Such mixtures, where the different components are generally visible with the naked eye or with a magnifying device, are non-uniform in nature.

   The chapter's example: sprout salad (Fig. 8.2).

   Two more: sand and water; muddy water. Others from the chapter's own tables — oil and water, carbon particles in air, baking powder (baking soda and tartaric acid), and Sample A in Activity 8.5, where you can see the black iron and yellow sulfur specks side by side.

   ✦ Note the phrase or with a magnifying device. A mixture does not stop being non-uniform because the pieces are small. If a magnifying glass or a microscope can still pick out separate components, it is non-uniform. The line is drawn at whether the components can be distinguished at all, not at whether your unaided eye happens to manage it.

3. 33 marksCuriosity Grade 8, Chapter 8, page 117

   What is a uniform mixture? Why does the chapter say sugar water is one, when Chapter 7 showed the sugar is still there?

   Hint. There is no contradiction — being present and being distinguishable are different things.

   Some mixtures have components that cannot be seen separately even with the help of a microscope. For example, sugar and water particles cannot be seen separately in their mixture. Such types of mixtures, where the components are evenly distributed and cannot be distinguished, are uniform in nature.

   Both statements are true at once. Chapter 7 showed the sugar is still present — the top layer tastes sweet without stirring. This chapter says its particles cannot be distinguished from the water particles. The sugar has not gone anywhere; it has spread into the interparticle spaces of the water so evenly that no instrument can point to a region and call it sugar.

   ✦ Evenly distributed is the operative phrase. Take a spoonful from the top of a properly dissolved sugar solution and a spoonful from the bottom, and they are the same. Try that with sprout salad and you get quite different spoonfuls. That is the real test of a uniform mixture, and it works even when your eyes cannot help you.

   Other uniform mixtures the chapter names: air, seawater, vinegar (acetic acid in water), aerated water, and all alloys.

4. 43 marksCuriosity Grade 8, Chapter 8, page 118

   What are alloys? Name the three the chapter gives and say what each is made of.

   Hint. The chapter introduces them in the 'A step further' box on stainless steel.

   Stainless steel contains iron, nickel, chromium, and a small amount of carbon. They are mixed so uniformly that the entire mixture appears the same throughout and one cannot see the individual substances. Such mixtures are known as alloys.

   Alloy	Made of
   Stainless steel	Iron, nickel, chromium and a small amount of carbon
   Brass	Copper and zinc
   Bronze	Copper and tin

   ✦ An alloy is a mixture, not a compound, and that is the point worth holding on to. The metals are mixed, not chemically combined, which is why the chapter puts alloys in Table 8.1 as a solid-and-solid mixture and calls them uniform. It is also why the proportions can be adjusted — a compound would have a fixed ratio and no choice about it.

   Why bother making them? Section 8.4 answers: they have developed alloys like stainless steel, which is stronger and more durable than pure iron. Mixing lets you design a material with properties that no single metal has.

5. 54 marksCuriosity Grade 8, Chapter 8, page 118

   What was Mishraloha, and what does the chapter's example of Kamsya tell you about how alloys were understood in ancient India?

   Hint. Read the 'Our scientific heritage' box, and note the exact proportions it gives.

   Mishraloha was the name given to the mixture of two or more metals that had properties distinct from its constituent metals. Ancient Indian texts, such as the Charaka Samhita, Susruta Samhita, Rasaratna Samucchaya, Rasa Jala Nidhi, etc., mention the use of alloys for medicinal purposes. For example, Bronze, also known as Kamsya, is an alloy made up of Copper (Tamra, 4 parts) and Tin (Vanga, 1 part), was used to improve digestion and boost immunity.

   What the definition shows. Mishraloha is defined by exactly the idea this chapter teaches — a mixture of metals that had properties distinct from its constituent metals. The whole reason for making an alloy was already understood: you mix in order to get something neither metal gives you alone.

   ✦ And the proportions were recorded, not left to chance. Tamra, 4 parts and Vanga, 1 part is a written recipe. Somebody had worked out that the proportion matters and that it must be repeatable, which is the beginning of quantitative chemistry.

   A note on the medicinal claim. The chapter reports what the texts say these preparations were used for. That is a historical statement about a practice, not a medical recommendation, and an accurate answer keeps it that way — the texts record the use; the chapter does not test whether it works.

6. 63 marksCuriosity Grade 8, Chapter 8, page 120

   In everyday speech the components of a mixture may themselves be mixtures. What extra condition does science impose, and why does it matter?

   Hint. The chapter draws this line explicitly before it can define a pure substance.

   The components of a mixture may themselves be mixtures, as in poha and sprout salad, or pure substances like sugar or common salt dissolved in water. However, in science, all the components of a mixture must be pure substances only.

   ✦ Without this rule, 'component' would never bottom out. Poha is a mixture of rice, oil, onion and spices; but onion is itself a mixture, and so is oil. If you are allowed to stop anywhere, you can call almost anything a component of almost anything and the word carries no information. Requiring components to be pure substances forces the analysis all the way down to substances that cannot be broken up any further by physical means.

   It also changes what separation is for. In everyday life ... separation is done to obtain the component of interest and other components are discarded. However, in science, the purpose of separating a mixture is to obtain pure substances. Winnowing throws the husk away; a chemist keeps both halves, because both are results.

7. 74 marksCuriosity Grade 8, Chapter 8, page 120

   Complete the third column of Table 8.1 for all the examples given, marking each as uniform or non-uniform.

   Hint. Ask in each case whether the components could be picked out — by eye, by lens, or by microscope.

   Mixture type	Example	Uniform or non-uniform
   Gas and gas	Air	Uniform (given)
   Gas and liquid	Aerated water (soda water)	Uniform
   Gas and liquid	Oxygen dissolved in water	Uniform
   Solid and gas	Carbon particles in air	Non-uniform
   Liquid and liquid	Acetic acid in water (vinegar)	Uniform
   Liquid and liquid	Oil and water	Non-uniform
   Solid and liquid	Sand and water	Non-uniform
   Solid and liquid	Seawater	Uniform
   Solid and solid	Baking powder (baking soda and tartaric acid)	Non-uniform
   Solid and solid	Alloys	Uniform

   ✦ The two pairs in rows 4 and 5 are the ones to study, because in each pair the type of mixture is identical and the answer still differs. Oil and water are both liquids and stay in two visible layers; vinegar is two liquids you cannot tell apart. Sand and seawater are both solid-in-liquid, but the sand sits there in plain view while the salt has dissolved. So the physical states of the components do not decide uniformity — whether the components are distinguishable does.

   Carbon particles in air is soot: visible specks drifting in a gas, which is why it is non-uniform, and why the chapter treats such particles as pollutants rather than as part of the air.

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.