Matter, possessing mass and volume, is made of atoms and molecules. It’s either a pure substance (element or compound with fixed composition and properties) or a mixture (physical combination of substances). Mixtures are homogeneous (uniform) or heterogeneous (non-uniform). Simple physical methods like filtration, evaporation, etc., can separate mixtures. The chapter introduces these fundamental concepts of matter and its basic classifications.
EXERCISE
Question 1.
Define matter.
Ans:
Matter is anything that has mass and occupies space (volume).
Question 2.
What is the difference between mass and weight.
Ans:
Mass is the unchanging amount of matter in an object, measured in kilograms (kg). It determines how hard it is to move the object.
Weight is the force of gravity pulling on that mass, measured in Newtons (N).
Question 3.
If an object weighs 6 N on earth what will be its weight on moon. What will be the change in its mass?
Ans:
Weight on the Moon will be 1 N (Earth’s gravity is about 6 times stronger than the Moon’s).
The mass of the object will not change; the change in mass is 0 kg. Mass is constant regardless of location.
Question 4.
Write your observation and conclusion for the following:
(a) When few marbles are put in a glass half filled with water.
(b) Ice is kept at room temperature.
Ans:
(a) Marbles in water: Observation: Water level rises as marbles submerge. Conclusion: Marbles occupy space and displace an equal volume of water.
(b) Ice at room temperature: Observation: Ice melts into liquid water, eventually warming to room temperature. Conclusion: Heat from the surroundings causes ice (solid water) to change its state to liquid water by increasing the kinetic energy of water molecules and overcoming intermolecular forces, eventually reaching thermal equilibrium.
Question 5.
State three main characteristics of the particles of matter.
Ans:
Matter’s particles are:
- Tiny: Too small to see.
- Spaced out: Have gaps between them (least in solids, most in gases).
- Always moving: Vibrate (solids) or move freely (liquids/gases).
Question 6.
Differentiate between an atom and a molecule.
Ans:
| Atom | Molecule |
| It is the smallest part of an element.It does not have independent existence. | It is the smallest part of a compound.It has an independent existence. |
Question 7.
Define :
(a) Solid
(b) Liquid
(c) Gas
Ans:
(a) Solid: A solid is a state of matter that has a definite shape and a definite volume. The particles (atoms, ions, or molecules) in a solid are closely packed together in a fixed arrangement and can only vibrate about their fixed positions. Due to these strong intermolecular forces and fixed particle arrangement, solids are generally rigid and incompressible.
(b) Liquid: A liquid is a state of matter that has a definite volume but no definite shape. It takes the shape of its container. The particles in a liquid are close together but have enough kinetic energy to move past each other. This allows liquids to flow and adapt to the shape of their container, but their volume remains constant because the particles are still relatively close and experience significant intermolecular forces. Liquids are generally incompressible.
(c) Gas: A gas is a state of matter that has neither a definite shape nor a definite volume. It expands to fill the entire volume of its container and takes the shape of the container. The particles in a gas are far apart from each other and move randomly and rapidly with high kinetic energy. The intermolecular forces between gas particles are very weak. Due to the large spaces between particles, gases are highly compressible.
Question 8.
Why are liquids and gases called as fluids.
Ans:
Liquids and gases are both classified as fluids due to their fundamental ability to flow. This characteristic stems from the relatively weak intermolecular forces present in these states of matter, allowing their constituent particles to move past one another with ease. Unlike solids, which possess a rigid structure and resist changes in shape, fluids readily adapt to the contours of their containing vessels.
A key defining property of fluids is their inability to resist shear stress. When subjected to a force applied parallel to their surface, fluids will undergo continuous deformation, or flow, as long as the stress is maintained.This lack of inherent resistance to shear stress distinguishes them from solids, which exhibit elastic deformation up to a certain limit and then resist further deformation.
In essence, the shared capacity for flow and the common inability to sustain shear stress in a static equilibrium are the primary reasons why both liquids and gases are collectively categorized under the term “fluids.” This unifying characteristic is crucial in understanding their behavior and how they interact with their surroundings.
Question 9.
(a) Define interconversion of states of matter.
(b) Why do solids, liquids and gases differ in their physical state?
(c) Under what conditions do solids, liquids and gases change their state.
Ans:
(a) Interconversion of states: This is when a substance changes between solid, liquid, and gas forms (like ice to water to steam) by gaining or losing energy, usually heat. The substance itself doesn’t change chemically.
(b) Difference in states: Solids, liquids, and gases differ because their particles (atoms/molecules) are arranged and move differently, and the forces holding them together vary. Solids have tightly packed, fixed particles with strong forces; liquids have closer but mobile particles with weaker forces; gases have far-apart, fast-moving particles with very weak forces.
(c) Conditions for state change: Changes in temperature and/or pressure cause substances to change state. Heating can cause melting (solid to liquid), boiling/vaporization (liquid to gas), or sublimation (solid to gas). Cooling can cause freezing (liquid to solid), condensation (gas to liquid), or deposition (gas to solid). Pressure changes can also affect these transition temperatures.
Question 10.
Give reasons :
(a) When a stone is dipped in a glass containning some water the level of water rises but when a spoon of sugar is added to it and stired, the water level does not rise?
(b) A drop of ink added to water in a glass turns whole water blue.
Answer:
(a) Stone vs. Sugar in Water: A stone has a definite volume and displaces water, causing the level to rise. Sugar dissolves into individual molecules that fit into the spaces between water molecules, so the volume increase is minimal and often unnoticeable.
(b) Ink in Water: Ink particles are in constant motion and spread out, moving into the spaces between water molecules. This process, called diffusion, leads to the uniform mixing of ink throughout the water, turning it blue.
Question 12.
Name the terms for the following :
(a) The change of a solid into liquid.
(b) The force of attraction between the molecules of matter.
(c) The particles of matter which may or may not have independent existence.
(d) The process due to which a solid directly changes into its vapours.
(e) The change of vapour into a liquid.
Ans:
(a) Melting.
(b) Intermolecular force of attraction.
(c) Solid.
(d) Sublimation.
(e) Condensation.
Question 13.
Classify the following into solid, liquid and gas :
Coal, kerosene, wood, oxygen, sugar, blood, water vapour, milk, wax.
Ans:
Solid: Coal, Wood, Sugar, Wax
Liquid: Kerosene, Blood, Milk
Gas: Oxygen, Water vapour
