Discover, Design and Debate — Projects — Particulate Nature of Matter

1. 14 marksCuriosity Grade 8, Chapter 7, page 115, project 1

   Fix a balloon over the neck of a bottle and put the bottle in hot water. Explore what will happen.

   Hint. Predict before you look, and be clear about what is inside the bottle.

   What is actually in the experiment. The bottle looks empty, but it is full of air — and air is matter, made of constituent particles. The balloon seals it in, so nothing can get in or out.

   Predict first, then test. Write down what you expect before putting the bottle into the hot water.

   What happens. The balloon inflates, standing up over the neck of the bottle.

   The explanation, from this chapter. The movement of particles increases when heat is provided — the Think-like-a-scientist result from the potassium permanganate test. The air particles inside the bottle move faster and spread further apart, and since gases tend to occupy the entire available space, they push out into the only space available: the balloon.

   ✦ What has NOT happened, and this is the part worth getting right. No new air has entered the bottle — the balloon seals it completely. The same particles are there, in the same number. They have simply spread out because their thermal energy increased. Saying 'hot air was created' or 'air came in from the water' would miss the whole point of the chapter.

   Extensions to report:

   • Move the bottle to cold water and watch the balloon shrink again. This is the reverse process and it shows nothing was lost.
   • Try hotter and less hot water and compare how far the balloon inflates.
   • Try it with the bottle half full of water instead, and say what difference you expect before testing.

   Be careful with hot water, and do this with a teacher or an adult present.

2. 24 marksCuriosity Grade 8, Chapter 7, page 115, project 2

   Design and create simple models to represent the particles of solids, liquids and gases, showing interparticle spacing, using clay balls, beads or similar materials.

   Hint. Three models, and the differences between them are the whole content.

   Materials. Clay balls, beads, marbles or table-tennis balls — plus three trays or shallow boxes of the same size to hold them.

   What to build:

   Model	How to arrange the balls	What it shows
   Solid	Balls packed closely and regularly, touching, in neat rows, filling the tray	Minimum interparticle spacing, strongest attraction, particles cannot change places
   Liquid	The same number of balls, close together but in no regular pattern, filling a little more of the tray	A little more spacing, slightly weaker attraction, particles move within a limited space
   Gas	The same number of balls, scattered widely across the whole tray with large gaps	Maximum spacing, negligible attraction, free movement

   ✦ Three rules that decide whether the models are correct:

   1. The same number of balls in all three. Changing state rearranges particles; it does not create or destroy them.
   2. The same size of ball in all three. Particles move further apart — they do not grow.
   3. Only the spacing and the arrangement change. That is the entire difference between the states.

   Two honest limitations to state in your report — a model that admits what it cannot show is a better model:

   • Nothing in a static model moves. In real matter, solid particles vibrate, liquid particles move within a limited space and gas particles move freely in all directions. You could add arrows, or shake the trays gently to different degrees.
   • The gaps are not filled with air. In your model there is air between the balls; in real matter they contain nothing at all (page 109). Say so.
3. 34 marksCuriosity Grade 8, Chapter 7, page 115, project 3

   Pretend to be particles of solids, liquids and gases at different temperatures — create and perform a role-play or dance showing particles in motion.

   Hint. The one thing a role-play can show that a clay model cannot is movement.

   Why this project exists. A model made of beads shows spacing but not motion. A role-play shows exactly the thing the models cannot: how particles move in each state, and how that movement changes with temperature.

   How to choreograph it:

   State	What the group does
   Solid	Stand shoulder to shoulder in neat rows, arms linked. Sway and shuffle on the spot but never leave your place — only vibrations
   Solid being heated	Sway harder and harder, straining against the linked arms
   Melting	The links break and people begin changing places, but stay bunched together within the marked area
   Liquid	Move around each other continuously, staying close and inside the marked space — movement restricted to limited space
   Boiling	Move faster and faster until people break away from the group
   Gas	Move freely and fast in all directions, spreading right across the room — movement in all the available space

   ✦ The transitions are the most valuable part of the performance, not the three states. Anyone can stand still for 'solid'. What the chapter actually explains is how one state becomes another: vibrations growing more vigorous until particles leave their fixed positions (melting), and movement growing until particles escape altogether (boiling). Show the build-up, not just the before and after.

   Add a temperature dimension. Perform the liquid section three times — as ice-cold, room-temperature and hot water — moving at three visibly different speeds. That is the Think-like-a-scientist result acted out: the movement of particles increases when heat is provided.

   Keep the number of people constant throughout. If some performers leave the stage for the gas section, the performance is showing particles being destroyed, which is exactly wrong.

4. 44 marksCuriosity Grade 8, Chapter 7, page 115, project 4

   Debate in class: 'Gases can spread and fill all the available space.' Is this property of gases beneficial or harmful?

   Hint. The same property does both, which is what makes it a debate and not a question.

   The property itself is not in dispute — Activity 7.5 demonstrates it, and the Snapshot states it: gases have no fixed shape and volume and tend to occupy the entire available space. The debate is about its consequences.

   Beneficial:

   Example	Why the spreading helps
   The fragrance of incense or flowers filling a room	Activity 7.9 — the pleasure depends entirely on gases spreading
   Oxygen reaching every part of a room, so we can breathe anywhere in it	No mixing would be needed if gases did not spread
   A room aired by opening a window	Stale air disperses and fresh air spreads in on its own
   Cooking smells reaching the whole house	The reason you know food is ready

   Harmful:

   Example	Why the spreading harms
   A leaking cooking-gas cylinder	The gas fills the kitchen rather than staying near the leak — dangerous, though it is also why you smell it and can act
   Smoke from a fire spreading through a building	Reaches rooms far from the fire itself
   Air pollution	Pollutants released in one place do not stay there

   ✦ The honest conclusion is that it is neither, and the same example often sits on both sides. A gas leak spreads through a kitchen because gases spread — and the only reason anyone notices it in time is that the smell spreads too. The property is not good or bad; what matters is which gas, and whether we want it where it is going.

   Close the debate with a better question: not is this property beneficial? but how do we make use of it where it helps and contain it where it does not? That is what sealed cylinders, exhaust fans, chimneys and ventilation are all for.

Solutions written by the tuition.in editorial team and checked against NCERT Curiosity, Textbook of Science for Grade 8, Chapter 7 'Particulate Nature of Matter', book pages 98-115 (hecu107.pdf, 18 pages, Reprint 2026-27), downloaded from ncert.nic.in and read page by page. Every activity number, figure number, quantity and quoted sentence below was checked against that PDF. Fig. 7.16 (exercise 8) was rendered and read: 7.16a shows a just-extinguished candle with solid wax in the body and set drips, liquid wax pooled round the wick, and vapour rising from the wick; 7.16b gives three particle boxes - regular close-packed (solid), close but irregular (liquid), and a few widely scattered particles (gas). Table 7.1's melting points were transcribed exactly: ice 0 C, urea 133 C, iron 1538 C. Three deliberate restraints. (1) The chapter covers ONLY melting point and boiling point, with evaporation mentioned in two sentences as prior learning. Sublimation, deposition, condensation, freezing, the factors affecting evaporation, evaporative cooling and the effect of pressure on state changes appear NOWHERE in this book and appear nowhere here. (2) The Acharya Kanad box gives no date - the chapter says only 'ancient Indian philosopher' and names the Vaisheshika Sutras - so no century is supplied, and the solution notes explicitly that dating estimates differ and would need a cited source. (3) Atoms and molecules are introduced only as the chapter's final 'A step further' box introduces them, with its own closing limit quoted: 'You will learn about atoms and molecules in higher grades.' Nothing about atomic structure or chemical formulae is added.. Questions are referenced from the NCERT textbook for identification.