Solute, Solvent and Solution — "The Amazing World of Solutes, Solvents, and Solutions"

1. 13 marksCuriosity Grade 8, Chapter 9, pages 135-136

   Define solution, solute and solvent. Write the relationship between them.

   Hint. The solid-in-liquid case first — the two-liquid case has its own rule.

   A uniform mixture, such as that of salt or sugar, and water, is called a solution. Whenever a solid is mixed with a liquid to form a solution, the solid component is called the solute, and the liquid component is called the solvent. The solute dissolves in the solvent to form a solution.

   Solute + Solvent → Solution

   Term	What it is	In salt water
   Solute	The substance that dissolves	Salt
   Solvent	The substance it dissolves in	Water
   Solution	The uniform mixture that results	Salt water

   ✦ A solution is a mixture, and every rule about mixtures still applies. Nothing has reacted, so the salt is still salt and can be recovered by evaporating the water — which is exactly what happens on the seashore in the opening picture and in the salt pans at Ningel. Dissolving is a physical change, not a chemical one.

   Solution is also just another name for one thing you already know. Uniform mixtures are called solutions, and their components are not visible separately. Air, seawater and vinegar were called uniform mixtures in Chapter 8; they are solutions.

2. 23 marksCuriosity Grade 8, Chapter 9, page 135

   When two liquids are mixed, which one is the solute and which the solvent? Why is a special rule needed?

   Hint. With a solid and a liquid it is obvious; with two liquids it is not.

   When a solution is formed by mixing two liquids, it is not always clear which substance is dissolving the other. In such cases, the substance present in smaller amount is called the solute, while the one in larger amount is called the solvent.

   Why a rule is needed. With salt and water you can see which substance vanished into which — the salt disappeared into the water, so the roles are obvious. Mix vinegar and water and nothing visibly disappears into anything; both are clear liquids and the result is a clear liquid. Since appearance cannot decide it, the chapter decides by quantity instead.

   ✦ Note that this is a convention, not a discovery. It is a sensible agreement about how to use two words, adopted so that everyone describes the same mixture the same way. Calling it a rule of nature would be wrong.

   Worked example. In vinegar, acetic acid is present in a small amount and water in a large one — so acetic acid is the solute and water the solvent. In a mixture of 90 mL of milk with 10 mL of water, the water is the solute.

3. 33 marksCuriosity Grade 8, Chapter 9, page 136

   Chashni for gulab jamun is a large amount of sugar in a small amount of water, yet the water is still called the solvent. Does this contradict the two-liquid rule?

   Hint. Check which rule applies before applying it.

   No — the two rules cover different cases, and chashni is not the two-liquid case.

   The Chashni (sugar syrup) of the Indian sweet Gulab jamun is made of a large amount of sugar (solid) dissolved in a small amount of water (liquid). However, the water is still considered as the solvent and sugar as the solute!

   Case	Which rule applies
   Solid in a liquid	The solid is always the solute, the liquid always the solvent — whatever the amounts
   Liquid in a liquid	The smaller amount is the solute, the larger the solvent

   ✦ The chapter includes chashni precisely because it looks like an exception. The 'smaller amount' rule was introduced only because with two liquids there is no other way to tell them apart — so it never had any business being applied when one component is a solid. Reaching for the wrong rule is the mistake this example is designed to catch.

   A useful check. Ask first: are both components liquids? If not, the solid is the solute and the liquid is the solvent, and quantity does not enter into it.

4. 43 marksCuriosity Grade 8, Chapter 9, page 135

   Air is a mixture of gases. Would a mixture of gases also be considered a solution?

   Hint. The chapter poses this as a student's question and answers it two pages later.

   Yes. A solution is a uniform mixture, and air is one — the gases are evenly distributed and cannot be distinguished from one another.

   The chapter confirms it twice. On page 139, of gases dissolved in water: It is a uniform mixture because the gases dissolve evenly in water. And the summary on the same page: Uniform mixtures are called solutions, and their components are not visible separately.

   The chapter's own exercise settles it too. Exercise 1(v) asks whether the presence of different gases in the atmosphere is also a uniform mixture — and the answer is true.

   ✦ What this shows is that a solution need not be liquid. The everyday picture of a solution is something in a glass, but the definition says nothing about states. Since the definition is 'uniform mixture' and nothing more, a mixture of gases qualifies, and so does an alloy — Chapter 8 called stainless steel, brass and bronze uniform mixtures of solids.

   (Which gas would be the solute in air? By the smaller-amount rule, oxygen, argon, carbon dioxide and water vapour are the solutes and nitrogen, at about 78%, the solvent.)

5. 53 marksCuriosity Grade 8, Chapter 9, page 135

   Sand, sawdust and chalk powder in water do not form solutions. What kind of mixture do they form, and how would you tell without a microscope?

   Hint. The chapter gives Fig. 9.2 for exactly this comparison.

   They form non-uniform mixtures.

   When salt and sugar are mixed with water, a uniform mixture is formed, whereas when chalk powder or sand, or sawdust is mixed with water, the components are not evenly distributed. Such mixtures are known as non-uniform mixtures.

   Three tests you can do without any instrument:

   1. Look. The sand and sawdust remain visible as separate particles; the salt does not.
   2. Wait. The sand settles to the bottom and the sawdust rises to the top. A solution stays as it is.
   3. Sample. Take a spoonful from the top and one from the bottom. In a solution they are identical; here they are not.

   ✦ Note the different behaviour of the two non-uniform mixtures, which the chapter's student character raises directly: in some non-uniform mixtures, such as sawdust in water, the sawdust floats, whereas in the mixture of sand and water, the sand sinks. I wonder why that happens? Both are non-uniform, and yet they separate in opposite directions — and answering that question is what sections 9.4 and 9.5 of this chapter are for.

6. 63 marksCuriosity Grade 8, Chapter 9, pages 135-136

   Classify each as solute, solvent or solution: seawater, the salt in seawater, the water in seawater, chashni, oxygen dissolved in a pond, ORS.

   Hint. For each, ask what role it plays in which mixture.

   	Role	In what
   Seawater	Solution	Salt (and other solids) dissolved in water
   The salt in seawater	Solute	It is the solid that dissolves
   The water in seawater	Solvent	It is the liquid that does the dissolving
   Chashni	Solution	Sugar (solute) in water (solvent)
   Oxygen dissolved in a pond	Solute	A gas dissolved in the solvent water
   ORS	Solution	Salt and sugar, both solutes, in water

   ✦ The same substance can hold different roles in different mixtures, and that is worth being clear about. Water is the solvent in every entry above, but in a mixture of 90 mL of oil with 10 mL of water, the water would be the solute by the smaller-amount rule.

   Also note that a solution may have more than one solute. ORS has two — salt and sugar — dissolved in a single solvent. Nothing in the definition limits a solution to one of each, which is why every sip of ORS tastes the same in both respects at once.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity — Textbook of Science for Grade 8, Chapter 9 (hecu109.pdf), Reprint 2026-27, pages 134-151. Questions are referenced from the NCERT textbook for identification.