9th Class Chemistry Chapter 1 States of Matter and Phase Changes – Notes and MCQs (KPK New Syllabus)

Chapter 1 of 9th class Chemistry (as per the new syllabus / National Curriculum) introduces the states of matter, the difference between elements, compounds and mixtures, and the changes of state such as melting, boiling and sublimation. These basic ideas are used in every later chapter and are a regular source of MCQs and short questions in the KP board exams.

Key Notes

1. Matter and its States

Matter: Anything that has mass and occupies space.

• Solid: Definite shape and definite volume. Particles are closely packed in fixed positions and only vibrate. Strong forces of attraction. Almost incompressible.
• Liquid: Definite volume but no definite shape (takes the shape of the container). Particles are close but can slide past one another. Can flow.
• Gas: No definite shape or volume. Particles are far apart and move randomly at high speed. Weak forces of attraction. Highly compressible.
• Plasma: The fourth state of matter. It is an ionized gas containing free electrons and positive ions. Found in the Sun and stars, lightning, neon signs and fluorescent tubes. It conducts electricity.

2. Kinetic Molecular Idea

Matter is made of tiny particles that are always moving. The particles have more kinetic energy when the temperature is higher. The forces between particles (intermolecular forces) are strongest in solids, weaker in liquids and weakest in gases.

3. Elements, Compounds and Mixtures

Element: A pure substance made of only one kind of atom; cannot be broken into simpler substances by chemical means. Examples: hydrogen, oxygen, iron, carbon.

Compound: A pure substance formed when two or more elements combine chemically in a fixed ratio by mass. Its properties differ from its elements. Examples: water (H2O), carbon dioxide (CO2), common salt (NaCl).

Mixture: Two or more substances physically mixed in any ratio; each keeps its own properties and can be separated by physical methods (filtration, evaporation, distillation, magnet).

• Homogeneous mixture: Same composition throughout, e.g. air, salt solution, brass (copper + zinc).
• Heterogeneous mixture: Composition not uniform, e.g. sand and water, soil, oil and water.

Allotropes: Different forms of the same element in the same physical state, e.g. diamond, graphite and fullerene are allotropes of carbon; oxygen (O2) and ozone (O3) are allotropes of oxygen.

4. Solutions, Colloids and Suspensions

• True solution: Homogeneous; particles are very small (less than 1 nm); transparent; particles do not settle; passes through filter paper. Example: sugar in water.
• Colloid: Particle size between about 1 nm and 1000 nm; particles do not settle; shows the Tyndall effect (scattering of a light beam). Examples: milk, fog, starch solution.
• Suspension: Heterogeneous; large particles that settle down on standing and can be separated by filtration. Example: chalk in water, muddy water.

5. Physical and Chemical Changes

Physical change: Only the state or appearance changes; no new substance is formed; usually reversible. Examples: melting of ice, dissolving sugar, boiling water.

Chemical change: A new substance with new properties is formed; usually not easily reversible. Examples: rusting of iron, burning of paper, cooking food.

6. Phase Changes

• Melting (fusion): solid → liquid. Melting point of pure ice = 0 °C at 1 atm.
• Freezing: liquid → solid.
• Evaporation: liquid → gas at the surface at any temperature. It causes cooling.
• Boiling: liquid → gas throughout the liquid at the boiling point. Water boils at 100 °C at sea level (1 atm).
• Condensation: gas → liquid.
• Sublimation: solid → gas directly, without becoming liquid. Examples: iodine, naphthalene (moth balls), dry ice (solid CO2), ammonium chloride.
• Deposition: gas → solid directly, e.g. formation of frost.

During a phase change of a pure substance, the temperature remains constant because the heat supplied (latent heat) is used to change the state, not to raise the temperature.

اردو میں خلاصہ

مادہ وہ چیز ہے جس میں کمیت ہو اور جو جگہ گھیرے۔ مادے کی چار حالتیں ہیں: ٹھوس، مائع، گیس اور پلازما۔ ٹھوس کی شکل اور حجم دونوں مقرر ہوتے ہیں، مائع کا صرف حجم مقرر ہوتا ہے جبکہ گیس کا نہ شکل مقرر ہوتی ہے نہ حجم۔ پلازما آئنائزڈ گیس ہے جو سورج اور ستاروں میں پائی جاتی ہے۔ عنصر ایک ہی قسم کے ایٹموں سے بنتا ہے، مرکب عناصر کے کیمیائی ملاپ سے مقررہ تناسب میں بنتا ہے، جبکہ آمیزہ اشیاء کا طبعی ملاپ ہے۔ ٹھوس کا براہ راست گیس بن جانا تصعید (سبلیمیشن) کہلاتا ہے، جیسے آیوڈین اور نیفتھلین۔

Important Short Questions

1. Why do gases have no definite shape or volume?
   Because their particles are far apart, the forces between them are very weak and they move freely in all directions, filling the whole container.
2. What is plasma? Give two examples.
   Plasma is an ionized gas made of free electrons and positive ions. Examples: the Sun and lightning.
3. Differentiate between a compound and a mixture.
   A compound has a fixed composition and its components combine chemically and lose their properties. A mixture has variable composition and its components keep their properties and can be separated physically.
4. What are allotropes? Give an example.
   Different forms of the same element in the same physical state, e.g. diamond and graphite (carbon).
5. What is the Tyndall effect?
   The scattering of a beam of light by colloidal particles, making the path of the light visible.
6. Why does evaporation cause cooling?
   The faster (high-energy) particles escape from the surface, so the average kinetic energy of the remaining liquid decreases and its temperature falls.
7. What is sublimation? Give examples.
   Direct change of a solid into a gas without becoming liquid, e.g. iodine, naphthalene and dry ice.
8. Why does temperature remain constant during melting?
   The heat supplied is used to overcome the forces between particles (latent heat), not to increase their kinetic energy.

20 MCQs

1. Which state of matter has a definite shape and a definite volume?
   (a) solid (b) liquid (c) gas (d) plasma
2. The fourth state of matter is:
   (a) vapour (b) plasma (c) colloid (d) solution
3. The direct change of a solid into a gas is called:
   (a) evaporation (b) condensation (c) sublimation (d) melting
4. The direct change of a gas into a solid is called:
   (a) freezing (b) deposition (c) boiling (d) fusion
5. Which of the following sublimes on heating?
   (a) common salt (b) iodine (c) sugar (d) sand
6. Particles move most freely in:
   (a) solids (b) liquids (c) gases (d) ice
7. Diamond and graphite are:
   (a) compounds of carbon (b) allotropes of carbon (c) mixtures (d) isotopes of oxygen
8. Water is a:
   (a) compound (b) element (c) mixture (d) colloid
9. Air is an example of a:
   (a) compound (b) element (c) homogeneous mixture (d) suspension
10. Milk is an example of a:
    (a) true solution (b) colloid (c) element (d) compound
11. The Tyndall effect is shown by:
    (a) a true solution (b) a colloid (c) pure water (d) salt solution
12. The melting point of pure ice at 1 atm is:
    (a) 0 °C (b) 4 °C (c) 100 °C (d) −10 °C
13. The boiling point of pure water at sea level is:
    (a) 0 °C (b) 50 °C (c) 100 °C (d) 273 °C
14. Evaporation causes:
    (a) heating (b) cooling (c) no change in temperature (d) melting
15. Rusting of iron is a:
    (a) physical change (b) chemical change (c) phase change (d) sublimation
16. Melting of ice is a:
    (a) chemical change (b) physical change (c) nuclear change (d) deposition
17. The change of a gas into a liquid is called:
    (a) condensation (b) evaporation (c) sublimation (d) freezing
18. A substance made of only one kind of atom is called:
    (a) a compound (b) a mixture (c) an element (d) a solution
19. Brass is a mixture of:
    (a) copper and tin (b) copper and zinc (c) iron and carbon (d) zinc and tin
20. Compressibility is highest in:
    (a) solids (b) liquids (c) gases (d) metals

Answer Key

1. (a)
2. (b)
3. (c)
4. (b)
5. (b)
6. (c)
7. (b)
8. (a)
9. (c)
10. (b)
11. (b)
12. (a)
13. (c)
14. (b)
15. (b)
16. (b)
17. (a)
18. (c)
19. (b)
20. (c)

These notes are prepared by Zama Taleem as per the KP Textbook Board syllabus. Always study from your official textbook too.