Class: 09
Science Revision Notes
Chapter – 2 Is Matter Around Us Pure ?
We do know that matter is made up of
particles which are arranged in a certain way. Gases particles are well separated
and can freely move about, solids, on the other hand, have particles that are
tightly packed, usually with no scope to move around.
Purity
Pure substances
- Pure
substances are elements or
compounds.
- They are made up of only one
kind of entity.
- They cannot be broken down into
simpler entities by chemical or physical methods.
- They have a fixed composition.
- Example: Diamond, carbon dioxide.
Mixtures
- Mixtures are formed by just mixing two or more pure substances
(components) such that each substance retains its own chemical
identity.
Types of mixtures
Types:
1. Homogeneous mixture
A mixture which has a uniform composition throughout is
called a homogeneous mixture or solution.
- Examples: sugar in water, salt in water.
Heterogeneous mixture
A mixture which contains physically distinct parts and has a
non-uniform composition is called a heterogeneous mixture.
- Examples: Mixture of salt and iron filings, sand and
sugar.
Physical vs Chemical Changes
Physical and chemical changes
- A substance is said to undergo
a physical
change when only the physical
properties such as the shape, size, colour or state of the substance
change. No new substance is formed.
- Example: Melting of ice,
boiling water.
- A substance is said to undergo
a chemical
change when a new substance with
completely new properties (physical and chemical) is formed.
- Example: Burning of wood or
paper, souring of milk.
Solutions
Solutions and their properties
- A solution is a homogeneous mixture of two or more
substances.
Properties:
- Its particles are too tiny and
have a diameter less than 1 nm.
- The particles are not visible
to naked eyes.
- Particles do not scatter a beam
of light passing through it and hence do not show the Tyndall effect.
- The solute particles never
settle down on keeping undisturbed.
- The components of
a solution cannot be separated using filtration.
Alloys
Alloys are homogeneous mixtures of metals or a mixture of a
metal and another element that cannot be separated into their components by
physical methods.
Examples:
- Steel, a combination of iron
(metal) and carbon (non-metal).
- Bronze, a combination of copper
(metal) and tin (metal).
- Brass, a mixture of copper
(metal) and zinc (metal).
Concentration of Solutions
Solubility
- Solubility is the property
showing the ability of a given substance, which is the solute, to dissolve
in a solvent.
- It is measured in terms of the
maximum amount of solute dissolved in a solvent at equilibrium.
- The resulting solution is
called a saturated solution.
- Factors
Affecting Solubility:
- Temperature – Solubility
increases with temperature. The situation is different for gases.
With the increase in temperature, they became less soluble in each
other and in water, but more soluble in organic solvents.
- Pressure – For the
majority of solid and liquid solutes, pressure does not affect solubility.
The solubility of gas is directly proportional to the pressure of this
gas.
Types of solutions based on the
concentration of the solution
- Three
types of solutions exist based
on the concentration of the solution:
Dilute
Concentrated
saturated solution.
Ways of representing the
concentration of a solution
The concentration of a solution can
be represented in many ways
(i) Mass by the mass percentage of a solution = (Mass of solute / Mass of solution) × 100
(ii) Mass by volume percentage of a
solution = (Mass of solute/ volume of
solution)×100
Suspensions
Suspension and its properties
A suspension is a heterogeneous mixture in
which the solute particles do not dissolve but remain suspended throughout the
bulk of the medium.
- The solute particles settle
down when a suspension is left undisturbed.
- They can be separated from the
mixture by filtration.
Colloids
Types of mixtures based on particle
size
Classified
into:
- Solution
- Suspension.
- Colloidal solution.
Colloidal Solutions
A colloidal solution is a mixture in which
the substances are regularly suspended in a fluid.
- Classified into: Foam,
Emulsion, Sol
Tyndall Effect
Tyndall effect is
the scattering of light by particles in a colloid or else particles in a very
fine suspension.
- e.g.It can be observed when
sunlight passes through the canopy of a dense forest.
Dispersed phase
The solute-like component of the
dispersed particles in a colloid form the dispersed phase.
Dispersion medium
The component in which the dispersed
phase is suspended is known as the dispersing medium.
Aerosol
A colloidal solution with dispersed
phase solid/liquid and dispersing medium gas is called Aerosol. e.g. clouds
Foam
A colloidal solution with dispersed
phase gas and dispersing medium solid/liquid is called Foam. e.g.Shaving cream.
Sols
A colloidal solution with dispersed
phase solid and dispersing medium liquid is called Sol. e.g. Milk of magnesia, mud.
Gels and emulsions
- A colloidal solution with
dispersed phase liquid and dispersing medium solid is called Gel.
- A colloidal solution with
dispersed phase liquid and dispersing medium liquid is called Emulsion.
Evaporation
The process of conversion of water into water vapour is
known as evaporation.
- It can be used to separate the
volatile component (solvent) from its non-volatile solute.
Introduction to Separation
Separation of components of a
mixture
- Heterogeneous mixtures can be
separated into their constituents by simple physical methods.
- Methods
include: handpicking, sieving,
filtration.
Handpicking Sieving
Separation of Two Immiscible Liquids
Separation of a mixture of two
immiscible liquids
- Separation of a mixture of two
immiscible liquids is done by using a separating funnel.
- Applications: To separate a mixture of oil and water, in the
extraction of iron from its ore.
Centrifugation
- Centrifugation uses centrifugal force for the separation of two
liquids in a mixture.
- Here, a denser component of the
mixture migrates away from the axis, and lighter component migrates
towards the axis.
Sublimation
Sublimation is
the transition of a substance from solid phase to gaseous phase without
changing into liquid phase.
- Example: Naphthalene balls undergo sublimation.
Solid
undergoing sublimation
Chromatography
- Chromatography is used to separate the different components in a
liquid mixture.
- It is based on the different
properties of compounds in two phases:
stationary and mobile phase.
Distillation
Distillation is
a method for separating the component substances from a liquid mixture by
selective evaporation and condensation.
- Used
in: Production of gasoline,
distilled water, xylene, alcohol, paraffin, kerosene etc.
Fractional Distillation
Fractional Distillation is
the separation of a mixture into its component parts or fractions by their
melting points.
- This is the process of
separation of chemical compounds by their boiling point.
- The mixture is heated to a
temperature at which one or more fractions will vaporize.
Separation of Air into Its Components
Process of obtaining different gases
from the air
Air is a homogeneous mixture and can
be separated into its components by fractional distillation
Fractional
distillation
Crystallization
- Crystallisation is a separation technique in which solids are
separated from a solution.
- In this technique, the solvent
molecules start evaporating, leaving behind the solutes when the solution
is heated in an open container.
Water Purification
Applications of crystallisation
Purification of seawater, separation
of alum crystals from impure samples etc.
Elements
- Elements are species of atoms which have the same number
of protons in their atomic nuclei.
- Elements are represented
by symbols e.g.Hydrogen (H), Boron (B), Carbon (C), Silicon
(Si) etc.
Metals
- Metal is a solid material which is typically hard,
shiny, malleable, fusible, and ductile, with good electrical and thermal
conductivity.
- Examples: Aluminium, Copper, Iron, Tin, Gold
Metalloids
- Metalloids exhibit some properties of metals as well as of
non-metals.
- Examples: Boron, silicon, germanium, arsenic, antimony, and
tellurium
Compounds
Nonmetals
- Non-metals are brittle and are not malleable or ductile.
- They are poor conductors of
heat and electricity.
- Examples: Carbon, Boron etc.
Compounds
Compounds are
the substances consisting of two or more different types of elements in a fixed
ratio of its atoms.
Difference between mixtures and
compounds
- Mixtures are constituted by more than one kind of pure
form of matter, known as a substance.
- Types: Homogeneous Mixtures, Heterogeneous Mixtures
- When two or more elements
chemically combine in a fixed ratio by mass, the obtained product is known
as a compound.
------------------------------------------------end------------------------------------------------------------------------- Mahesh Patteed,M.Sc.B.Ed (9620139001) Email : patted.mahesh6@gmail.com
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