Chapter 9 of 23

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Tamil Nadu (TNBSE)Class 10 Science★ 4-7 marks in the TN SSLC Class 10 Science public exam through MCQs, short answers and concentration numericals

Solutions

Samacheer Kalvi (TN State Board) Class 10 Science — Chemistry Chapter 9, Solutions. Composition and types of solutions, concentration (mass and volume percentage), solubility, hydrated and anhydrous salts with water of crystallisation, and efflorescent, deliquescent and hygroscopic substances. Notes with definitions, worked numericals, common mistakes, practice and quick revision.

⏱ 18 min readEasy difficulty✓ Free · NCERT-aligned

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By the end of this chapter you'll be able to…

1Define solution, solute and solvent
2Calculate mass and volume percentage concentration
3Explain solubility and types of solutions
4Describe water of crystallisation in hydrated salts
5Distinguish efflorescent, deliquescent and hygroscopic substances

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Why this chapter matters

Solutions explains concentration and how salts behave with water in air — efflorescence, deliquescence and hygroscopy — concepts that appear as reliable definition and reasoning questions in the TN SSLC Science exam.

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Chapter 7 — Atoms and Molecules

Formulae and masses of compounds.

Solutions — Class 10 Science (Samacheer Kalvi)

TN State Board (Samacheer Kalvi) Class 10 Science, Chemistry — Chapter 9. Mixtures, concentration, and how salts interact with water in the air.

1. About this chapter

This chapter covers solutions (solute + solvent), their concentration, solubility, hydrated/anhydrous salts, and the special behaviour of efflorescent, deliquescent and hygroscopic substances.

2. Solution, solute and solvent

A solution is a homogeneous mixture of two or more substances.
Solute = substance dissolved (smaller amount); solvent = substance that dissolves it (larger amount). Water is the universal solvent.
Types by amount of solute: dilute, concentrated, saturated (no more solute dissolves at that temperature), unsaturated, and supersaturated.

3. Concentration of a solution

Mass percentage = (mass of solute / mass of solution) × 100.
Volume percentage = (volume of solute / volume of solution) × 100.
Solubility: the maximum amount of solute that dissolves in 100 g of solvent at a given temperature.

4. Hydrated salts and water of crystallisation

Water of crystallisation: the fixed number of water molecules chemically combined in a crystal. e.g. CuSO₄·5H₂O (blue), Na₂CO₃·10H₂O (washing soda).
Hydrated salt: contains water of crystallisation; anhydrous salt: has none (e.g., white anhydrous CuSO₄).

5. Efflorescence, deliquescence, hygroscopy

Term	Behaviour	Examples
Efflorescent	hydrated salt loses water of crystallisation to air, turning powdery	Na₂CO₃·10H₂O
Deliquescent	absorbs so much moisture it dissolves into a solution	NaOH, CaCl₂, MgCl₂
Hygroscopic	absorbs moisture but does not dissolve	conc. H₂SO₄, silica gel, quicklime (CaO)

6. Worked examples

Example 1. 20 g of salt is dissolved in 80 g of water. Find the mass percentage of the solution. Mass of solution = 20 + 80 = 100 g; mass % = (20/100)×100 = 20%.

Example 2. Why does washing soda become powdery when left in air? It is efflorescent — it loses its water of crystallisation to the air.

Example 3. Why is anhydrous calcium chloride used as a drying agent? It is deliquescent / hygroscopic — it absorbs moisture from the surroundings.

7. Common mistakes

Mistake: Confusing deliquescence with efflorescence. Fix: Efflorescent salts lose water; deliquescent substances absorb water and dissolve.
Mistake: Calling every mixture a solution. Fix: A solution must be homogeneous.
Mistake: Mixing up hygroscopic and deliquescent. Fix: Hygroscopic absorbs moisture but does not dissolve; deliquescent dissolves.

8. Practice (book-back style)

Define a solution; name the solute and solvent in sugar syrup.
What is water of crystallisation? Give an example.
Differentiate efflorescent and deliquescent substances.
25 g of solute in 100 g of solution — find the mass percentage.
Why is silica gel placed in packaging?

9. Answer key

A homogeneous mixture; in sugar syrup sugar is the solute, water the solvent.
The fixed water molecules combined in a crystal; e.g., CuSO₄·5H₂O.
Efflorescent loses water of crystallisation to air; deliquescent absorbs moisture and dissolves.
Mass % = (25/100)×100 = 25%.
It is hygroscopic and keeps the contents dry by absorbing moisture.

10. Quick revision

Chemistry Ch 9 · solutions, concentration, hydrated salts.
Solution = homogeneous mixture (solute + solvent).
Mass % = (solute/solution)×100; saturated = max solute at that temperature.
Water of crystallisation: CuSO₄·5H₂O, Na₂CO₃·10H₂O.
Efflorescent loses water; deliquescent absorbs & dissolves; hygroscopic absorbs but does not dissolve.

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Mass percentage

(mass of solute / mass of solution) × 100

Mass of solution = solute + solvent.

Volume percentage

(volume of solute / volume of solution) × 100

For liquid-in-liquid solutions.

Solubility

max solute in 100 g solvent at given T

Usually increases with temperature for solids.

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Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Confusing deliquescence with efflorescence

✓ Efflorescent salts lose water; deliquescent substances absorb water and dissolve.

WATCH OUT

✗ Calling every mixture a solution

✓ A solution must be homogeneous.

WATCH OUT

✗ Mixing up hygroscopic and deliquescent

✓ Hygroscopic absorbs moisture but does not dissolve; deliquescent dissolves.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Multiple choice questions

MCQs on solutions, concentration and salt behaviour.

Questions

Short answer questions

Definitions, water of crystallisation and the three special behaviours.

Questions

Numerical problems

Mass and volume percentage calculations.

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Concept

Define a solution.

▶ Show solution

A homogeneous mixture of two or more substances (solute dissolved in solvent).

Q2EASY· Numerical

20 g of salt is dissolved in 80 g of water. Find the mass percentage.

▶ Show solution

Mass of solution = 100 g; mass % = (20/100)×100 = 20%.

Q3MEDIUM· Concept

What is water of crystallisation? Give an example.

▶ Show solution

The fixed number of water molecules chemically combined in a crystal, e.g. CuSO₄·5H₂O (blue vitriol).

Q4MEDIUM· Comparison

Differentiate efflorescent and deliquescent substances with examples.

▶ Show solution

Efflorescent: loses water of crystallisation to air, e.g. Na₂CO₃·10H₂O. Deliquescent: absorbs moisture and dissolves, e.g. NaOH, CaCl₂.

Q5EASY· Application

Why is silica gel placed in packaging?

▶ Show solution

It is hygroscopic and keeps the contents dry by absorbing moisture without dissolving.

Q6EASY· Recall

Give one hygroscopic substance.

▶ Show solution

Concentrated sulphuric acid (also silica gel, quicklime).

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Chemistry Chapter 9 of Samacheer Kalvi Class 10 Science.
•Solution = homogeneous mixture (solute + solvent).
•Mass % = (solute/solution)×100; saturated = max solute at that temperature.
•Water of crystallisation: CuSO₄·5H₂O, Na₂CO₃·10H₂O.
•Efflorescent loses water; deliquescent absorbs and dissolves.
•Hygroscopic absorbs moisture but does not dissolve.

Tamil Nadu (TNBSE) marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4-7 marks across MCQ, short answer and numerical questions

Question type	Marks each	Typical count	What it tests
MCQ	1	1-2	Definitions and examples
Short Answer	2-3	1-2	Water of crystallisation, salt behaviour
Numerical	2	1	Mass / volume percentage

Prep strategy

Learn mass and volume percentage formulas
Memorise examples of hydrated salts
Separate efflorescent / deliquescent / hygroscopic with examples
Practise concentration numericals

Where this shows up in the real world

This chapter isn't just an exam topic — it lives in the world around you.

Drying agents

Silica gel and CaCl₂ keep medicines and electronics dry.

Everyday solutions

Sugar syrup, salt water and soda are common solutions.

Testing for water

Anhydrous copper sulphate detects the presence of water.

Exam strategy

Battle-tested tips from teachers and toppers for this chapter.

Use the mass-percentage formula carefully (solution = solute + solvent)
Give an example for each special term
Write hydrated-salt formulas with the dot and water
Keep definitions precise

Going beyond the textbook

For olympiad aspirants and curious learners — topics that build on this chapter.

Calculate the percentage of water of crystallisation in CuSO₄·5H₂O.
Explain why deliquescent salts make poor laboratory standards.

Where else this chapter is tested

CBSE board isn't the only one — other exams test this chapter too.

TN SSLC Class 10 Public ExamHigh

Foundation / NTSE ChemistryMedium

School unit testsHigh

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Questions students ask

The real ones — pulled from the Q&A community and tutor sessions.

White anhydrous CuSO₄ takes up water of crystallisation to form hydrated CuSO₄·5H₂O, which is blue — this is used as a test for water.

Both absorb moisture from air, but a hygroscopic substance stays solid while a deliquescent substance absorbs so much water that it dissolves into a solution.

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