Discover, Design and Debate — Projects — "The Amazing World of Solutes, Solvents, and Solutions"

1. 14 marksCuriosity Grade 8, Chapter 9, page 151

   Research project on the Dead Sea: why is there no aquatic life in it? Find out whether there are any other similar water bodies.

   Hint. Two chapter ideas meet here — how much can dissolve, and what dissolved salt does to a liquid's density.

   What to investigate, and the science you already have for it.

   1. How salty is it, and how does that compare with ordinary seawater? Find a figure from a checked source and record where you found it. This is a question about concentration — solute in a fixed quantity of solvent.
   2. Why would that prevent aquatic life? Bring together two threads from this chapter: what such a concentration would do to organisms, and section 9.3's point that dissolved oxygen is what sustains all aquatic life.
   3. Why do people float in it so easily? Dissolved salt raises the water's density, which is the egg experiment on page 148 at natural scale.
   4. Are there other such water bodies? Look for other hypersaline lakes and see what they have in common — how they are fed, and whether water leaves them by evaporation rather than by an outflowing river.

   ✦ Discipline for the research. Use at least two independent sources for any number you quote, and report it if they disagree rather than picking the first one you saw. Salinity figures vary with depth, season and the method of measuring, so a range with its source is a better answer than a single confident number.

   Say clearly which parts of your answer are explanation and which are looked-up fact. The density argument you can derive yourself from this chapter; the salinity figure you cannot.

2. 24 marksCuriosity Grade 8, Chapter 9, page 151

   Investigate how well common salt dissolves in different solvents — water, vinegar and oil. Compare and record your observations.

   Hint. Design it as a fair test before you start measuring anything.

   Designing the test. For the comparison to mean anything, everything except the solvent must be held constant:

   Hold constant	Why
   Volume of solvent — say 50 mL each	Solubility is defined per fixed quantity of solvent
   Amount of salt added per step — one level spoon	So the counts can be compared
   Temperature	Solubility changes with it, so all three must be at the same temperature
   Stirring — same time, same vigour	Stirring changes the rate, and unequal stirring would confuse rate with limit

   What to record. For each solvent, the number of spoons that dissolved completely before solid began to settle, and what the mixture looked like at the end.

   ✦ Predict before you observe, and write the prediction down. Chapter 9 has already told you that sugar and salt dissolve in water but not in oil, and Chapter 7 explained why: the solvent's particles must be able to pull the solute's particles apart. Since oil particles cannot do this to salt, you should expect essentially none to dissolve — and if your observation disagrees with your prediction, that is a result worth investigating, not an error to hide.

   Report honestly what 'does not dissolve' looked like. Salt sitting unchanged at the bottom of the oil is a genuine observation, and recording no measurable dissolution is a real answer rather than a failed experiment.

3. 34 marksCuriosity Grade 8, Chapter 9, page 151

   Debate in class: is water truly the most versatile solvent? How would you argue each side?

   Hint. The chapter gives evidence for both sides on the same page.

   The case for water.

   • It dissolves an exceptional range of substances — salts, sugars, and gases including the oxygen that sustains all aquatic life.
   • 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.
   • It is abundant, cheap and safe to handle — a practical advantage no other solvent matches.
   • Every solution in this chapter's first half uses it: ORS, seawater, chashni, the baking soda of Activity 9.2.

   The case against.

   • Plenty of things do not dissolve in it — sand, chalk, sawdust, oil, and the constituent particles of any substance held together too strongly for water particles to pull apart.
   • The same heritage box names alternatives that traditional medicine used deliberately: oils, ghee, milk, and other substances as solvents, and hydro-alcoholic extracts of the herbs.
   • Asima Chatterjee used solvents and solutions extensively — plural, because different compounds need different solvents.

   ✦ The strongest position is a precise one rather than a side. Water is the most versatile solvent for a very wide class of substances and by far the most useful in practice — and it is not universal, because if it were, no one would ever have needed a second solvent. Saying exactly what is being claimed is what turns a debate into an argument.

4. 44 marksCuriosity Grade 8, Chapter 9, page 151

   Describe how salt is produced traditionally at Ningel village, and identify the chapter's science in each step.

   Hint. Follow the process and name what is happening chemically at each stage.

   The process, as the chapter gives it.

   Ningel village in Manipur's Thoubal district is a place where salt is still produced using traditional methods. The village has a few salt wells, one of which is lined with a 100-year-old tree trunk placed into the ground to draw up salty water. A few families mostly women, continue this sacred practice by collecting the salt solution and boiling it in large metal pans over firewood kilns. Once the water evaporates and salt crystals form, they are shaped into round 'salt cakes' using banana leaves and handmade tools. These cakes are then wrapped in a traditional cloth (phanek) to protect them.

   The science, step by step:

   Step	What is happening
   Drawing salty water from the well	The groundwater is a solution — salt is the solute, water the solvent
   Boiling it in metal pans	The solvent is driven off as vapour; the solute cannot evaporate
   Salt crystals forming	As water leaves, the solution becomes more concentrated, reaches saturation, and the excess salt comes out as solid
   Shaping and wrapping the cakes	Keeping the dry salt from taking up moisture again

   ✦ This is the opening picture of the chapter, done deliberately and at a well instead of a shore. Separating a solute from its solvent by evaporation is a physical change — because nothing has reacted, the salt recovered is the same salt that was dissolved. Chapter 8 made the same point: dissolved sodium chloride may be separated from water by the physical process of evaporation.

   The chapter's closing line is worth keeping as it is written: Salt in Ningel is more than just food — it is history, culture, belief, and a beautiful example of India's living heritage. The medicinal value is reported as something the cakes are believed to have, and an accurate answer keeps that wording.

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.