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CBSE Class 8 · Science

The Amazing World of Solutes, Solvents, and Solutions

Official NCERT chapter from Curiosity (book code hecu1). ExamMaster notes are original teaching at CBSE Class 8 depth.

This lesson follows the official chapter “The Amazing World of Solutes, Solvents, and Solutions” in Curiosity. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 8
  • Easy level
  • 8 concepts

1What Are Solute, Solvent, and Solution?

A solution is a mix that looks the same throughout: solute (the stuff that dissolves) in a solvent (the stuff that does the dissolving). Salt in water: salt is solute, water is solvent. A sandy glass with visible bits is not this solution.

Oil sitting as a layer is not a solution of oil-in-water.

Figure. Solute dissolves in solvent to make a uniform solution. Salt + water → salt water. Sand in water is not a solution: the bits stay visible.

How it works

  1. Name solute and solventThis pair.
  2. See a same-throughout look after a fair stirThe solution.
  3. If bits or a layer remain, it is not this solutionA different mix.

2How Much Solute Can a Fixed Amount of Solvent Dissolve?

A fixed amount of solvent can dissolve only so much solute at a given temperature, as taught. That limit is solubility in the classroom sense: add more and extra sits undissolved. Warming can change the limit if the lesson showed it.

“It will all dissolve if I wait forever” is not this fair-stir limit.

Figure. A fixed amount of water dissolves only so much salt. Unsaturated: more can still dissolve. Saturated: extra salt sits undissolved at the bottom.

How it works

  1. Fix the solvent amount and the temperatureThe given.
  2. Add solute until extra remains after a fair stirThe limit.
  3. Call that the how-much of this pairSolubility-as-taught.

3Solubility of Gases

Gases dissolve in liquids too: a fizzy drink holds a gas that leaves when you open it (pressure-story as taught). Warming often drives gas out — a flat warm drink is a look. Solubility of gases is its own heading, not the salt-story copied.

A bubble you blew with a straw is not the dissolved gas.

Figure. Gases dissolve less as water warms. About 12.8 mg/L of O₂ at 5 °C against 8.3 mg/L at 25 °C. Cold water holds more oxygen for fish; a warm soda goes flat faster.

How it works

  1. Name a gas-in-liquid as taughtFizz.
  2. See it leave when pressure drops or warmth rises, if that was shownThe look.
  3. Keep it different from salt’s limitA gas-story.

4Why Do Objects Float or Sink in Water?

Float or sink in water: compare the object’s density to water’s, as this chapter names density next. A closed bottle of air floats; a steel pin may sink. “Heavy” is not enough — a heavy log can float.

A steel ship’s story is a later-or-aside look; here, stay with density-compare if that is the lesson.

Figure. Same-size wood and iron: wood sits on the water line and floats; iron sits on the floor and sinks. Heavy versus light is the wrong test — density is the property.

How it works

  1. Ask which is denser, object or water, if you have the numbers or the taught ruleThe compare.
  2. Denser → sink; less dense → float, as taughtThe sort.
  3. Refuse heavy-therefore-sinkThe log-miss.

5What Is Density?

Density is mass per volume: how much stuff in a box of space. A 2 kg bag in 1 L is denser than 2 kg in 4 L. Unit-pair as taught (g/cm³ or kg/m³). Density is the compare-word for float/sink.

The bigger object is not automatically denser.

Figure. Density is mass per volume. A 1 L oil pack at 910 g is 0.91 g/cm³; water is 1.00; aluminium 27 g in 10 cm³ is 2.7. Below the water rule floats; above it sinks.

How it works

  1. Measure or be given mass and volumeThe two parts.
  2. Divide mass by volumeDensity.
  3. Compare two densities with the same unitsThe job.

Which is denser?

Block A is 20 g in 10 cm³. Block B is 20 g in 25 cm³. Which is denser?

  • A20/10 = 2 g/cm³
  • B20/25 = 0.8 g/cm³
  • DenserA

Pro tip. Same mass, smaller volume → larger density.

6A definition is a test you can run

Solute / solvent / solution is a test: name the pair and the same-throughout look. If you cannot name which is dissolving in which, you have a glass of “stuff”.

A brand of drink is not the test.

Figure. A definition is a test you can run. After mixing: if bits are still visible it is not a solution; if every sip looks the same, it is.

How it works

  1. Name solute and solventThe object.
  2. See same-throughoutThe test.
  3. Then the words have contentThe definition ran.

7Name the given before the unknown

The given are the pair and the amounts (or mass and volume). The unknown is dissolve-limit, float/sink, or density. Copy volume before you call the bigger block denser.

A large foam block that is light is a silent given you skipped.

Figure. Name the given before the unknown. Given: mass 27 g and volume 10 cm³ of aluminium. The unknown is density, not a guess about float or sink.

How it works

  1. Copy mass, volume, or the pairThe given.
  2. Name density or dissolve or floatThe unknown.
  3. Then divide or compareGiven first.

8One worked case is enough at this class

One dissolve-limit or one density-compare is enough. A page of the same 20 g / 10 cm³ clone does not add a new fizz-story.

Ten twins of 2 g/cm³ are still one idea.

Figure. One worked case: 27 g ÷ 10 cm³ = 2.7 g/cm³. Relative to water at 1 g/cm³ the block is denser, so it sinks. Same numbers as the given-first step.

How it works

  1. Run one solution-case or one densityThe case.
  2. A second only as a checkOptional.
  3. StopThis class.
Density is
  1. Mass per volume — not “bigger therefore denser”
  2. Volume only
  3. Always larger for heavier-looking bags

Same mass, smaller volume → denser.

Notes

  • Mapped to the official NCERT chapter “The Amazing World of Solutes, Solvents, and Solutions”. Original teaching only — no textbook sentences.
  • Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.

Formulas

  • density = mass / volume

Recap

Hold these pegs from the official chapter “The Amazing World of Solutes, Solvents, and Solutions”. The wording is ExamMaster’s teaching, not a textbook recap.

What Are Solute, Solvent, and Solution?
A solution is a mix that looks the same throughout: solute (the stuff that dissolves) in a solvent (the stuff that does the dissolving).
How Much Solute Can a Fixed Amount of Solvent Dissolve?
A fixed amount of solvent can dissolve only so much solute at a given temperature, as taught.
Solubility of Gases
Gases dissolve in liquids too: a fizzy drink holds a gas that leaves when you open it (pressure-story as taught).
Why Do Objects Float or Sink in Water?
Float or sink in water: compare the object’s density to water’s, as this chapter names density next.
What Is Density?
Density is mass per volume: how much stuff in a box of space.
A definition is a test you can run
Solute / solvent / solution is a test: name the pair and the same-throughout look.

Practise The Amazing World of Solutes, Solvents, and Solutions

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