Probe and Ponder — The Opening Questions — "The Amazing World of Solutes, Solvents, and Solutions"

1. 13 marksCuriosity Grade 8, Chapter 9, page 134

   What do you think is happening in the picture that opens the chapter?

   Hint. Look at what the people are picking up from the ground, and where they are standing.

   What is shown. A crowd has gathered at the edge of the sea. The ground at the water's line is crusted white, and people are bending down to gather that white solid off the wet sand. The figure at the centre — an elderly man in a dhoti with a shawl, round spectacles and a long staff — is drawn as Mahatma Gandhi, and the scene is the making of salt at the seashore during the Salt March.

   ✦ The science in it is this chapter's opening idea. Seawater is a solution — salt dissolved in water. When seawater is left on the shore under the sun, the water evaporates and the salt, which cannot evaporate, is left behind as a white crust. So the people are not making salt; they are collecting a solute that the sea itself has separated from its solvent. That is exactly what the chapter's own heritage box describes at Ningel village, where salt water is boiled until the water evaporates and salt crystals form.

   A note on the history. The chapter prints the picture without a caption and does not name the event, so if you write about it, say where you checked. The chemistry, however, is in the picture whether or not you know the history — dissolved salt, evaporated water, salt left behind.

2. 23 marksCuriosity Grade 8, Chapter 9, page 134

   What happens when you add too much sugar to your tea and it stops dissolving? How can you solve this problem?

   Hint. The chapter answers both halves — one in Activity 9.1, the other in Activity 9.2.

   What has happened. The tea has reached its limit. When the solute stops dissolving and begins to settle at the bottom, the solution is called a saturated solution at that particular temperature. No amount of extra stirring will help, because the problem is not that the sugar has not been mixed in — it is that the liquid cannot hold any more at that temperature.

   How to solve it — three genuine ways:

   Fix	Why it works
   Heat the tea	For most of the substances, the solubility increases with an increase in temperature — a saturated solution behaves as an unsaturated one once warmed
   Add more tea (more solvent)	Solubility is the maximum solute per fixed quantity of solvent, so more solvent can hold more sugar
   Accept it and stop adding	The undissolved sugar at the bottom is simply not part of the solution

   ✦ Notice that stirring is not on the list. Stirring speeds dissolving up; it does not raise the limit. Activity 9.1 has you stir well at every stage and the salt still stops dissolving eventually, which is how you know the limit is real and not a failure of mixing.

   And there is a catch with the heating fix. As the tea cools again, the extra sugar it could hold at the higher temperature may come out at the bottom, because the limit falls back with the temperature.

3. 34 marksCuriosity Grade 8, Chapter 9, page 134

   Why do sugar and salt dissolve in water but not in oil? Why is water considered a good solvent?

   Hint. Recall from Chapter 7 what has to happen to a solid's particles for it to dissolve.

   Why they dissolve in water. Chapter 7 explained dissolving as a contest: the water particles ... pull out the particles of the solid from the grain, and the freed particles then occupy the interparticle spaces of the water. Water particles can do this to sugar and salt. In the case of many substances, the constituent particles are held together strongly that the water particles are unable to pull these out — that is why sand does not dissolve.

   Why not in oil. Oil particles do not pull salt and sugar particles apart the way water particles do. Since nothing separates the solute's particles, nothing dissolves, and the solid simply sits in the oil unchanged.

   Why water is called a good solvent. Because it dissolves a very wide range of substances — salts, sugars, many gases including the oxygen that aquatic life depends on, and the compounds used to make medicines. The chapter's heritage box makes the point historically: water has primarily been used as a solvent for the preparation of medicinal formulations in Ayurveda, Siddha, and other traditional systems of medicine in India.

   ✦ But note what the same box goes on to say: those traditions also used oils, ghee, milk, and other substances as solvents, and modern formulations use hydro-alcoholic extracts. So water is exceptionally versatile, not universal — which is precisely the question the chapter sets for the class debate on page 151.

4. 43 marksCuriosity Grade 8, Chapter 9, page 134

   Why are water bottles usually tall and cylindrical in shape instead of spherical?

   Hint. The chapter asks the same question about measuring cylinders on page 144.

   Several honest reasons, and the chapter supplies one of them directly.

   The one the chapter explains (page 144, about measuring cylinders): a tall narrow container gives a larger change in height for the same change in volume, so the level can be read far more precisely. In a wide, shallow container the same amount of water barely alters the level. A bottle marked with volume levels is easier to read for the same reason.

   Practical reasons that follow from shape:

   • A cylinder stands up on a flat surface; a sphere rolls away.
   • Cylinders pack together on a shelf or in a bag with far less wasted space than spheres.
   • A tall narrow neck is easy to grip and pour from without spilling.

   ✦ Be careful not to over-claim here. The chapter poses this as a Probe and ponder question — it is inviting you to think, not stating a single official answer. A good response gives reasons and says which one it is confident about, rather than inventing one authoritative cause. The reading-precision reason is the one the chapter itself later justifies, so lead with that.

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

   Why does every sip of homemade ORS taste the same — never salty in one sip and sweet in another?

   Hint. This is the chapter's own opening example, and the answer is one word from Chapter 8.

   Because ORS is a uniform mixture.

   When you add sugar and salt to water, they form a mixture in which the components are evenly distributed throughout.

   The salt and sugar particles have separated and spread evenly through the water, so every spoonful contains them in the same proportion. There is no region of the liquid that is 'the salty part'.

   ✦ Contrast this with a non-uniform mixture and the point becomes sharp. When chalk powder or sand, or sawdust is mixed with water, the components are not evenly distributed. Take a spoonful from the top of sandy water and one from the bottom and you get quite different spoonfuls. That is why the uniform/non-uniform distinction matters for something as practical as a medicine — a treatment that arrived in uneven doses would be no use at all.

   And it gives the chapter its first definition. A uniform mixture, such as that of salt or sugar, and water, is called a solution. ORS is a solution, and the whole chapter follows from asking how much can be dissolved, and why.

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.