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Chapter 9 · Solutes, Solvents and Solutions

NCERT Class 8 · Curiosity

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CHAPTER 9 OF 13

Solutes, Solvents and Solutions 🥤

Stir sugar into water and it seems to vanish. It has not — it has dissolved, and the result is a solution.

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Part 1 · The Words

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Part 2 · Saturation

Part 3 · Speeding Up

1

The three words 🥄

Get these three names right and half the chapter is done.

🥄 Naming the parts

WordMeaningIn sugar water
Solutethe substance that dissolvessugar
Solventthe one that does the dissolvingwater
Solutionthe two togethersugar water
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Water is called the universal solvent because it dissolves more substances than any other liquid. That is also why it is so easily polluted — almost anything will dissolve into it.

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Dissolved is not destroyed. The sugar is still there — you can taste it, and it reappears if the water evaporates. The total mass does not change either.

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Game 1 — Dissolves or Not?

2

Saturation and solubility 🧂

A solvent cannot take an unlimited amount. When no more will dissolve, the solution is saturated.

🧂 The three kinds of solution

KindMeaning
Unsaturatedmore solute can still dissolve
Saturatedno more will dissolve at that temperature
Supersaturatedholding more than it normally could, usually after heating and cooling gently
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Temperature matters, and in opposite ways. Heating makes solids dissolve more readily in water — but it makes gases dissolve less. That is why a warm fizzy drink goes flat quickly, and why warm river water holds less oxygen for fish.

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Game 2 — Saturation Facts

3

Speeding it up ⚡

Three things make a solid dissolve faster, and every one of them is a standard exam answer.

⚡ What makes dissolving faster

Do thisWhy it works
Stir itfresh solvent keeps meeting the solute
Heat itparticles move faster and mix sooner
Powder itmore surface is exposed to the solvent
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Why powdered sugar dissolves fastest. A lump touches the water only on its outside. Grinding it exposes far more surface, so far more of it can be attacked by the water at once.

Game 3 — Faster or Slower?

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Topic Mock Test

12 questions on solutions and solubility. 🍀

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Chapter 10 · Light 🔦