A group of cells that are similar in structure and/or work together to achieve a particular function forms a tissue.
Most of the tissues in plants are supportive, which provides them with structural strength.
These tissues are dead since dead cells can provide mechanical strength as easily as live ones, and need less maintenance.
Plant Tissues are of two types Meristematic & Permanent tissues.

A. MERISTEMATIC TISSUE

These are simple living tissues having thin-walled compactly arranged immature cells which are capable of division and formation of new cells.

FEATURES OF MERISTEMATIC TISSUE

Thin primary cell wall (cellulosic).
Intercellular spaces are absent (compact tissue).
Generally, vacuoles are absent, dense cytoplasm & prominent nuclei are present.
Large numbers of cell organelles are present.
Active metabolic state, stored food is absent.
Actively dividing cells are present in growing regions of plants, for example, root & shoot tips.

I. CLASSIFICATION OF MERISTEMATIC TISSUES ON THE BASIS OF ORIGIN

1. PRIMARY MERISTEMATIC TISSUE(PROMERISTEM)

Derived directly from the meristems of the embryo.
They consist of cells derived from the primary meristem.
They add to the primary growth of plants.

2. SECONDARY MERISTEMATIC TISSUE

Formed by permanent tissues.
These are having cells derived from primary permanent tissue.
They usually add to the diameter of plants.

II. CLASSIFICATION OF MERISTEMATIC TISSUES ON THE BASIS OF LOCATION

1. APICAL MERISTEM

It is present at the growing tips of stems and roots.
Cell division in this tissue leads to the elongation of stem & root, thus it is involved in the primary growth of the plant.

2. INTERCALARY MERISTEM

It is present behind the apex.
It is the part of the apical meristem which is left behind
during the growth period.
These are present at the base of the leaf & internode
region.
These lead to the increase in the length of leaf
(Primary), for example: in grass stem, bamboo stem, mint
stem etc.

3. LATERAL MERISTEM

It is also called secondary meristem.
It occurs along the sides of the longitudinal axis of the plant.
It gives rise to the vascular tissues.
Causes growth in girth of stem & root.
They are responsible for secondary growth.

B. PERMANENT TISSUE

The permanent tissues are composed of those cells which have lost their capability to divide.
They have a definite shape, size and thickness. The permanent tissue may be dead or living.
The division & differentiation of the cells of meristematic tissues gives rise to permanent tissues.
In cell differentiation, developing tissue and organs change from simple to more complex forms to become specialized for specific functions.
The cells of permanent tissue lose the capacity to divide and attain a permanent shape, size and function.
Permanent tissues are classified into two types on the basis of Structure and Composition i.e. Simple Permanent Tissues and Complex Permanent Tissues.

SIMPLE PERMANENT TISSUE

These are made up of same type of cells which are similar structurally and functionally.
They include two types of tissue Protective tissues and Supporting Tissues.

PROTECTIVE TISSUE

These tissues are primarily protective in function.
They consist of Epidermis and Cork/Phellem.

EPIDERMIS

Epidermis forms one cell thick outermost layer of various body organs of plants such as leaves, flowers, stems and roots.
The epidermis is covered outside by a cuticle. The cuticle is a water-proof layer of a waxy substance called cutin which is secreted by the epidermal cells.
The cuticle is very thick in xerophytes.
Cells of epidermis of leaves are not continuous at some places due to the presence of small pores called as stomata.
Each stomata is guarded by a pair of bean-shaped cells called as guard cells. These are the only epidermal cells which possess chloroplasts, the rest being colourless.

FUNCTIONS OF EPIDERMIS

The main function of the epidermis is to protect the plant from desiccation and infection.
The cuticle of the epidermis cuts the rate of transpiration and evaporation of water and prevents wilting.
Stomata in the epidermis allow the gaseous exchange to occur during photosynthesis respiration.
Stomata also help in transpiration.

CORK OR PHELLEM

In older roots and stems, tissues at the periphery become cork cells or phellem cells.
Cork is made up of dead cells with thick walls and does not have any intercellular spaces.
The cell walls in cork deposit a waxy substance called suberin.
The cells of cork become impermeable to water and gases due to the deposition of suberin.
The cork cells are without any protoplasm but are filled with resins or tannins.

FUNCTIONS OF CORK

Cork is protective in function.
Cork cells prevent desiccation, infection and mechanical injury.
Imperviousness, lightness, toughness, compressibility and elasticity make the cork commercially valuable.
Cork is used for insulation, like a shock absorber in linoleum.
Cork is used in the making of a variety of sports goods such as cricket balls, table tennis, shuttlecocks, wooden paddles etc.

SUPPORTING TISSUE

These are supportive in function.
There are three types of Supporting tissues i.e.
(i) Parenchyma,
(ii) Collenchyma and
(iii) Sclerenchyma.

(i) PARENCHYMA

It is the fundamental tissue.
Tissue first time evolved in bryophyte.
Thin-walled cells, oval or spherical in structure.
The cell wall mainly composed of cellulose & pectin.
Large central vacuole for food & water storage.
The primary function is food storage.
Some parenchyma involved in excretory substance storage is so-called idioblast, storing such as resin, tannin, gums & oils.
In typical parenchyma chlorophyll is absent.
Chloroplast containing parenchyma tissue are chlorenchyma which performs photosynthesis such as mesophyll of leaves.
In hydrophytic plants aerenchyma (a type of parenchyma containing air spaces) provides buoyancy.
Parenchyma provides turgidity to cells.

(ii) COLLENCHYMA

It is the living mechanical tissue.
Elongated cells with thick corners.
Localized cellulose & pectin thickening.
Provides flexibility to plant parts & easy bending of various parts of the plant.
Present only in herbaceous dicot stem.
Present at the thin margin of leaves.
Few chloroplasts may be present.
Gives mechanical strength & elasticity to the growing stems.

(iii) SCLERENCHYMA(SCLERAS-HARD) STRENGTHENING TISSUE

Composed of extremely thick-walled cells with little or no protoplasm.
Cells are dead & possess very thick lignified walls.
Lignin is water-proof material.
Intercellular spaces are absent.
Cells of sclerenchyma are of two types Sclereids and Fibres.

SCLEREIDS

These are also called grit cells or stone cells.
These are small cells, where the lumen is so small due to higher thickening of the cell wall, as present in fruit (mango, coconut, walnut) in legume seeds (Macrosclereid).

FIBRES

They are very long, narrow, thick, lignified cells. Lumen is large as compared to sclereids. They are generally 1-3 mm long.
In the thick walls of both the fibres and sclereids are present thin areas called as pits.
Sclrenchyma Fibres are used in the manufacture of ropes, mats & certain textile fibres.
Jute and coir are obtained from the thick bundle of fibres.

DIFFERENCE BETWEEN PARENCHYMA, COLLENCHYMA AND SCELERENCHYMA

COMPLEX PERMANENT TISSUE

It consists of more than one type of cells which work together as a unit.
It helps in transportation of organic materials, water & minerals.
It is also known as conducting or vascular tissue.
Xylem & phloem together form vascular bundles.

XYLEM

It is also known as wood and is a vascular and mechanical tissue.
Thick walled cells are found in the form of tubular passages.
Xylem consists of four types of cells called as elements Tracheids, Vessels, xylem parenchyma and xylem sclerenchyma.

(i)TRACHEIDS

They are elongated angular dead cells (primitive elements) mainly involved in conduction of water and minerals in gymnosperms.

(ii)VESSELS

They are advance element (generally found in angiosperms).
Vessels are cylindrical tube like structures placed one above the other end to end which form a continuous channel for efficient conduction of water.

(iii)XYLEM PARENCHYMA

They are small & thick walled parenchymatous cells subjected for storage of starch (food).

(iv)XYLEM SCLERENCHYMA

They are non-living fibres with thick walls and narrow cavities provide mechanical support.
Except xylem parenchyma all other xylem elements are dead.
The annual rings present in the trunk of a tree are xylem rings.
By counting the number of annual rings, we can determine the age of a tree.

PHLOEM

They also consist of both parenchymatous and schlerenchymatous cells.
Phloem consists of four types of element which are Sieve tubes, Companion cells, Phloem fibre and Phloem parenchyma.
In phloem, except phloem sclerenchyma, all elements are living.

(i) SIEVE TUBES

Sieve tubes are slender tube like structures made up of elongated, thin walled cells placed end to end.
The end walls of sieve tube cells are perforated by numerous pores, called as sieve plates.
Nucleus of sieve cell degenerates at maturity. However, cytoplasm persists, because of protoplasmic continuation of sieve tube with companion cell through plasmodesmata.
Sieve cells possess slime protein or protein which is concerned with growth and repair of sieve cells.

(ii) COMPANION CELLS

Companion cells have dense cytoplasm and prominent nuclei.
Sieve cells & companion cells are so called sister cells because they originate from single mother cell.

(iii) PHLOEM FIBRE

They give mechanical support to sieve tubes.

(iv) PHLOEM PARENCHYMA

They store food and help in radial conduction of food.

(v) LEPTOME

Main part of phloem involved in conduction of food, which is sieve tube.
In xylem, only unidirectional movement is possible while in phloem bidirectional movement can occur.

DIFFERENCE BETWEEN XYLEM AND PHLOEM

Everything in this universe is made of materials which scientist has names ‘matter’. The matter is made up of very small tiny particles. It is not continuous but is particulate. The matter is anything that occupies space and has mass. Particles of matter have space between them and are continuously moving. Particles of matter attract each other.

Matter can change its state from solid to liquid and from liquid to gas and vice-versa.

EFFECT OF TEMPERATURE

On increasing the heat, the particles gain energy and start vibrating with greater energy. Due to increased kinetic energy the particles overcome the force of attraction and a new state is obtained.

MELTING POINT

The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its melting point.

BOILING POINT

The temperature at which a liquid starts boiling at the atmospheric pressure is known as its boiling point.

LATENT HEAT OF FUSION

The amount of heat energy required to change 1 kg of a solid into liquid at its melting point is called the latent heat of fusion of the solid.

LATENT HEAT OF VAPOURIZATION

The amount of heat energy required to change 1 kg of a liquid to vapour at atmospheric pressure, at its boiling point is called the latent heat of vaporization of the liquid.

EFFECT OF PRESSURE ON THE MATTER

On applying pressure, the particles of matter can be brought close together and the state of matter can be changed. For example, CO2 gas can be solidified by applying pressure and lowering temperature.

EVAPORATION

The phenomenon of changing of a liquid into its vapour state at any temperature below its boiling point is called evaporation. Evaporation is a surface phenomenon.

Factors affecting evaporation:

1. An increase in surface area increases evaporation.
2. An increase in temperature increases the rate of evaporation.
3. A decrease in humidity increases the rate of evaporation.
4. An increase in wind speed increases the rate of evaporation.
5. Evaporation causes a cooling effect.

SOME MEASURABLE QUANTITIES AND THEIR UNITS

NOTE: Now scientists are talking of five states of matter: Solid, Liquid, Gas, Plasma and Bose-Einstein Condensate.

PLASMA

The state consists of super energetic and super excited particles.
These particles are in the form of ionised gases.
The fluorescent tube and neon sign bulbs consist of plasma.
Inside a neon sign bulb, there is neon gas and inside a fluorescent tube, there is helium gas or some other gas.
The gas gets ionised, that is, gets charged when electrical energy flows through it.
This charging up creates a plasma glowing inside the tube or bulb.
The plasma glows with a special colour depending on the nature of the gas.
The Sun and the stars glow because of the presence of plasma in them.
The plasma is created in stars because of very high temperature.

BOSE-EINTSEIN CONDENSATE

In 1920, Indian physicist Satyendra Nath Bose had done some calculations for the fifth state of matter.
Building on his calculations, Albert Einstein predicted a new state of matter – the Bose-Einstein Condensate (BEC).
The BEC is formed by cooling a gas of extremely low density, about one-hundred-thousandth the density of normal air, to super-low temperatures.
In 2001, Eric A. Cornell, Wolfgang Ketterle and Carl E. Wieman of the USA received the Nobel prize in physics for achieving “Bose-Einstein condensation”.

Anything which occupies space and has mass is called matter. Matter can be divided into two categories.
(i) Pure Substance: It consists of single types of particles that are the same in their chemical nature.
(ii) Mixtures: Mixture consists of two or more particles.

MIXTURE AND ITS TYPES

The mixture consists of more than one kind of pure substances which can be separated by physical method. It has two types (i) Homogeneous mixture (ii) Heterogeneous mixture

(i)HOMOGENEOUS MIXTURE

A mixture is said to be homogeneous if all the components of the mixture are uniformly mixed and there are no boundaries of separation between them. Ex: Sugar in water, etc.

(ii)HETEROGENEOUS MIXTURE

A mixture is said to be homogeneous if all the A mixture is said to be heterogeneous if all the components of the mixture are not uniformly mixed and there are visible boundaries of separation between them. Ex: Water and sand, Air etc.components of the mixture are uniformly mixed and there are no boundaries of separation between them. Ex: Sugar in water, etc.

SOLUTION AND ITS PROPERTIES

A solution is a homogeneous mixture of two or more substances. Ex: Lemonade, soda water etc. A solution has two types:(i) Solvent (ii) Solute

(i)SOLVENT

The component of the solution that dissolves the other component in it (usually the component present in larger amount) is called the solvent.

(ii)SOLUTE

The component of the solution that is dissolved in the solvent (usually present in lesser quantity) is called the solute.

PROPERTIES OF SOLUTION

1. A solution is a homogeneous mixture.
2. The particles of a solution are smaller than 1 nm (10-9) in diameter which cannot be seen by naked eyes.
3. They do not scatter a beam of light passing through the solution that is they don’t show tyndall effect. So, the path of light is not visible in a solution.
4. The solute particles cannot be separated from the mixture by the process of filtration.
5. The solution is stable and solute particles do not settle down when left undisturbed.

CONCENTRATION OF A SOLUTION

The concentration of a solution is the amount of solute present in a given amount (mass or volume) of solution. Also, the amount of solute dissolved in a given mass or volume of solvent is called concentration of solution.
Concentration of solution = Amount of solute/Amount of solvent or Amount of solute/Amount of solution (Here, amount means mass or volume).

(i) SATURATED SOLUTION

When no more amount of solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

(ii)UNSATURATED SOLUTION

When more amount of solute can be dissolved in a solution at a given temperature, it is called a saturated solution.

(ii)SOLUBILITY

The amount of the solute present in the saturated solution at the given temperature is called its solubility.

TWO METHODS OF FINDING CONCENTRATION OF A SOLUTION

(i) Mass by 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

SUSPENSION AND ITS PROPERTIES

A suspension is a heterogeneous mixture in which the the solute particles do not dissolve but remain suspended throughout the bulk of the medium. Ex: Chalk in water, smoke in the air

PROPERTIES OF SUSPENSION

1. It is a heterogeneous mixture.
2. Particles of a suspension are visible to the naked eye.
3. Size of the particles is greater than 100 nm.
4. It is unstable mixture. Solute settles down at the bottom over period of time.
5. If the solution is passed through filter paper, solute and solvent gets separated.
6. It scatters light when light is passed through the solution i.e. it shows Tyndall effect.

COLLOIDAL SOLUTION

Colloid solution is heterogeneous mixture in which the size of particles lies between the true solutions and suspensions. Colloidal particles can easily scatter a beam of visible light. This phenomenon is called Tyndall effect.

PROPERTIES OF COLLOIDAL SOLUTION

1. The particles of colloid can’t be seen by naked eyes individually.
2. It is a heterogeneous mixture and thus solute and solvent can’t be separated by filter paper.
3. Size of particles is smaller than suspensions but greater than solutions (1 nm to 100 nm).
4. It is a stable mixture. Particles do not settle down at the bottom over a period of time.
5. They do not settle down when left undisturbed which means colloid is quite stable.

SOME COMMON EXAMPLES OF COLLOIDS

SEPARATION OF COMPONENTS OF MIXTURE

Different methods of separation are used to get individual components from mixture. Heterogeneous mixtures can be separated into their respective constituents by simple physical methods like handpicking, sieving, filtration etc.

SUBMLIMATION

This process is used to separate mixtures that contain a sublimable volatile component from a non-sublimable impurity.
Sublimation is process where a substance directly changes from solid to gaseous state on heating.
Ammonium chloride, camphor, naphthalene and anthracene are some examples which can sublime.

CHROMATOGRAPHY

Used to separate those solutes which dissolve in the same solvent.
Used for sepration of colours.
The colours which are more soluble in water rises faster and get colours get separated into layers.

APPLICATIONS

To separate colours in a dye
To separate pigments from natural colours
To separate drugs from blood.

DISTILLATION

Used for separation of components of a mixture containing two miscible liquids that boil without decomposition and have sufficient difference in their boiling points.
Mixture of acetone and water is separated by this method.

FRACTIONAL DISTILLATION

Fractional distillation is used to separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K.
Air is a homogeneous mixture and can be separated into its components by fractional distillation.

The air is compressed by increasing the pressure and is then cooled by decreasing the temperature to get liquid air.
The liquid air is warm-up slowly in a fractional distillation column, where gases get separated at different heights depending upon their boiling points.
It used to separate a gas from the air.

CRYSTALLIZATION

Used to remove impurities from solid and purify it.
It separates a pure solid from mixture in the form of crystals. This process is used in purification of salt from sea water, separation of crystals of alum from impure samples.
It is better method than evaporation because:
(i) Solids decompose or some, like sugar, may get charred on heating to dryness.
(ii) Some impurities may remain dissolved in the solution even after filtration. On evaporation these contaminate the solid.

PHYSICS AND CHEMICAL CHANGES

The process which brings about changes in physical properties and no new substances are formed are physical changes.
The common physical changes are changes in colour, hardness, rigidity, fluidity, density, melting point, boiling point etc.
The process in which new substances are formed and chemical properties of substances get changed are chemical changes.
Some chemical properties are odour, inflammability etc.

PHYSICAL CHANGES

It brings about change in physical properties such as physical state, shape, size etc.
No changes in chemical compositions are observed.
It is reversible.
No new substance is formed.

CHEMICAL CHANGES

It brings about changes in chemical properties.
Changes in chemical properties are observed.
It is irreversible that means permanent
New substance is formed.

TYPES OF PURE SUBSTANCES

The pure substance is divided in two types on the basis of their chemical composition:
(i) Elements (ii) Compounds

(i) ELEMENTS

According to Antoine Laurent Lavoisier, an element is a basic form of matter that cannot be broken down into simpler substances by chemical reactions.
It is divided into three types which are metals, non-metals and metalloids.

PROPERTIES OF METALS

(i) They have a lustre (shine).
(ii) They have silvery-grey or golden-yellow colour.
(iii) They conduct heat and electricity.
(iv) They are ductile (can be drawn into wires).
(v) They are malleable (can be hammered into thin sheets).
(vi) They are sonorous (make a ringing sound when hit).
• Examples of metals are gold, silver, copper, iron, sodium, potassium etc.
• Mercury is the only metal that is liquid at room temperature.

PROPERTIES OF NON-METALS

(i) They display a variety of colours.
(ii) They are poor conductors of heat and electricity.
(iii) They are not lustrous, sonorous or malleable.
Examples of non-metals are hydrogen, oxygen, iodine, carbon (coal, coke), bromine, chlorine etc.

METALLOIDS

Elements having intermediate properties between those of metals and non-metals are called metalloids. Examples are boron, silicon, germanium etc.

(ii) COMPOUNDS

A compound is a substance composed of two or more elements, chemically combined in a fixed proportion.

DIFFERENCE BETWEEN MIXTURE AND COMPOUND

Around 500 B.C., Indian philosopher Maharishi Kanad, postulated the theory if we go on dividing matter (padarth), we will obtain the smallest particle beyond which further division can’t be possible which is known as ‘parmanu’.
1. Ancient Greek philosophers – Democritus and Leucippus called these particles atoms.
2. Antoine L. Lavoisier laid the foundation of chemical sciences by establishing two important laws of chemical combination.

LAWS OF CHEMICAL COMBINATION

• This law established after the experiments by Lavoisier and Joseph L. Proust.
• The chemical reaction between two or more substances give rise to products which are governed by certain laws called Laws of Chemical Combination.

LAW OF CONSERVATION OF MASS

During a chemical reaction, the total mass of reactants will be equal to the total mass of the products.
Mass can neither be created nor destroyed in a chemical reaction.
Example: A (reactant) + B (reactant) → AB (product)
mass of A + mass of B = mass of AB

LAW OF CONSTANT PROPORTIONS

In a chemical reaction, compounds always contain the same elements present in definite proportions by mass irrespective of their source.
It was given by Lavoisier.
For example:
(i) 18 gm of H2O = 2 gm of hydrogen + 16 gm of oxygen ⇒ mass of hydrogen/mass of oxygen = 2/16 = 1/8
(ii) 36 gm of H2O = 4 gm of hydrogen + 32 gm of oxygen
⇒ mass of hydrogen/mass of oxygen = 4/32 = 1/8
(iii) 9 gm of H2O = 1 gm of hydrogen + 8 gm of oxygen
⇒ mass of hydrogen/mass of oxygen = 1/8
This verifies law of constant proportions as the ratio of mass of hydrogen to oxygen is always same.

DALTON'S ATOMIC THEORY

According to Dalton’s atomic theory, all matter, whether an element, a compound or a mixture is composed of small particles called atoms.
Six Postulates of Dalton’s atomic theory:
(i) All matter is made of very tiny particles called atoms.
(ii) Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction.
(iii) Atoms of a given element are identical in mass and chemical properties. (Law of conservation of mass)
(iv) Atoms of different elements have different masses and chemical properties.
(v) Atoms combine in the ratio of small whole numbers to form compounds. (Law of constant proportion)
(vi) The relative number and kinds of atoms are constant in a given compound.

ATOMS

Atoms are building blocks of all matter.
According to modern atomic theory, an atom is the smallest particle of an element which takes part in chemical reaction.
Atoms are very small and which can’t be seen even through very powerful microscope.
Atomic radius is measured in nanometres. Nanometres = 10-9 m

MODERN DAY SYMBOLS OF ELEMENTS

Dalton was the first scientist to use the symbols for elements.
Berzilius suggested that the symbols of elements should be made from one or two letters of the name of the element.
The name copper was taken from Cyprus, a place from where it was found for first time.
Now, IUPAC (International Union of Pure and Applied Chemistry) approves names of elements.
The first letter of a symbol is always written as a capital letter (uppercase) and the second letter as a small letter (lowercase). For example: hydrogen (H), aluminium (Al), cobalt (Co).
Some other symbols have been taken from the names of elements in Latin, German or Greek. For example: Fe from its Latin name ferrum, sodium is Na from natrium, potassium is K from kalium.

ATOMIC MASS

Dalton’s atomic theory proposed the idea of atomic mass which explained the law of constant proportions so well.
The mass of an atom of an element is called its atomic mass.
In 1961, IUPAC have accepted ‘atomic mass unit’ (u) to express atomic and molecular mass of elements and compounds.
The atomic mass unit is defined as the quantity of mass equal to 1/12 of mass of an atom of carbon-12.
1 amu or u = 1/12 × Mass of an atom of C12 1 u = 1.66 × 10-27 kg

ATOM EXISTENCE

Atoms of most of the elements are very reactive and does not exist in free state.
Only the atoms of noble gases (such as He, Ne, Ar, Kr, Xe and Rn) are chemically unreactive and can exist in the free state as single atom.
Atoms of all other elements combine together to form molecules or ions.

MOLECULES

A molecule is in general a group of two or more atoms that are chemically bonded together
A molecule is the smallest particle of matter (except element) which is capable of an independent existence and show all properties of that substance.
Examples: ‘H2O’ is the smallest particle of water which shows all the properties of water.
A molecule may have atom of same or different elements, depending upon this, molecule can be categorized into two categories:
(i) Homo atomic molecules (containing atom of same element) Examples: H2, O2, O3, S8, P4 etc.
(ii) Heteroatomic molecules or compounds (containing atoms of different elements) Examples: H2O, CO2, NaCl, CaCO3etc.

ATOMICITY

The number of atoms present in one molecule of an element is called its atomicity.

CHEMICAL FORMULAE

It is the symbolic representation of the composition of a compound.

CHARACTERISTICS OF CHEMICAL FORMULAE

- The valencies or charges on ion must balance.
- When a compound is formed of metal and non-metal, symbol of metal comes first. E.g., CaO, NaCl, CuO.
- When polyatomic ions are used, the ions are enclosed in brackets before writing the number to show the ratio. E.g., Ca(OH)2 , (NH4)2SO4

RULES FOR WRITING CHEMICAL FORMULAE

We first write symbols of elements which form compound.
Below the symbol of each element, we should write their valency.
Now cross over the valencies of combining atoms.
With first atom, we write the valency of second atom (as a subscript).
With second atom, we write the valency of first atom (subscript).

MOLECULAR MASS

It is the sum of atomic masses of all the atoms in a molecule of that substance.
Example: Molecular mass of H2O = 2×Atomic mass of Hydrogen + 1×Atomic mass of Oxygen. So, Molecular mass of H2O = 2×1 + 1×16 = 18 u.

FORMULA UNIT MASS

It is the sum of atomic mass of ions and atoms present in formula for a compound. Example: In NaCl, Na = 23 a.m.u, Cl = 35.5 a.m.u.
So, Formula unit mass = 1×23 + 1×35.5 = 58.5 u.

IONS

An ion may be defined as an atom or group of atoms having positive or negative charge.
Some positively charged ions : Na+ , K+, Ca2+ , Al3+
Some negatively charged ions : Cl- (chloride ion), S2- (sulphide ion), OH- (hydroxide
ion), SO42- (sulphate ion)
We can classify ions in two types:
(i) Simple ions: Mg2+ (Magnesium ion),Na+ (Sodium ion)Cl- (Chloride ion), Al3+ (Aluminium ion)
(ii) Compound ions: NH4+ (Ammonium ion) CO32- (Carbonate ion) SO42- (Sulphate ion) OH- (Hydroxide ion)

CHEMICAL FORMULAE OF IONIC COMPOUNDS(POLYATOMIC) MOLE CONCEPT

A group of 6.022×1023 particles (atoms, molecules or ions) of a substance is called a mole of that substance.
1 mole of atoms = 6.022×1023 atoms
1 mole of molecules = 6.022 × 1023 molecules Example, 1 mole of oxygen = 6.022×1023 oxygen atoms
Note: 6.022×1023 is Avogadro Number (L).
1 mole of atoms of an element has a mass equal to gram atomic mass of the element.

MOLAR MASS

The molar mass of a substance is the mass of 1 mole of that substance.
It is equal to the 6.022×1023 atoms of that element/substance.
Examples:
Atomic mass of hydrogen (H) is 1 u. Its molar mass is 1 g/mol.
Atomic mass of nitrogen is 14 u. So, molar mass of nitrogen (N) is 14 g/mol.
Molar mass of S8 = Mass of S×8 = 32×8 = 256 g/mol
Molar mass of HCl = Mass of H + Mass of Cl = 1 = 35.5 = 36.5 g/mol

IMPORTANT FORMULAE

We can see many celestial bodies in a clear night sky.
Stars are one of the celestial bodies which emit light of their own.
The moon is a natural satellite of the Earth.
It revolves around the Earth in its orbit.
The different shapes of the bright visible part of the moon as seen from the Earth are called phases of the moon.
Sun is also one of the stars which emit light and is a great source of heat.
It is the closest star and is the centre of our solar system.
The stars are millions of km far from Earth and from each other.
Such large distances are expressed in a unit known as light year.
It is the distance travelled by light in one year, i.e., 9.46 × 1012 km.
Stars are many light years away from the Earth and thus they look very small from Earth. Stars appear to travel from east to west.
The Pole star is the most shining star in the night sky. The pole star appears to be stationary. It is situated near the axis of rotation of Earth and is thus helpful in finding direction.
Other important parts of the night sky are planets. Planets revolve around the Sun.
Our solar system consists of eight planets revolving around the Sun. It also consists of many other celestial bodies like asteroids, comets and meteors.
Inner or Terrestrial Planets: First four planets Mercury, Venus, Earth and Mars are much nearer to the Sun and have fewer satellites. They are called the inner planets. These are also called terrestrial planets because their structure is rocky similar to that of Earth.

JOVIAN PLANETS

The planets outside the orbit of Mars, namely Jupiter, Saturn, Uranus and Neptune are called outer planets because they are much farther off than inner planets. They are also known as Jovian planets because their structure is gaseous and are similar to that of Jupiter.

IMPORTANT FACTS ABOUT THE PLANETS:

MERCURY(BUDHA)

It is the closest planet to the Sun. Its distance from Sun is 57 × 106 km.
Since it is very close to the Sun, most of the time it is hidden in the glare of the Sun.
It can be visible before the Sunrise in the east and after the Sunset in the west.
It appears quite bright and correspondingly it is termed as ‘morning star’ and ‘evening star’.
It is termed a star because it appears very bright in the sky.
It is of the same size as the moon.
It revolves around the Sun in 88 days and takes 58 days to complete one rotation on its axis.
Life cannot exist on mercury due to lack of atmosphere and extreme temperature [340°C ⇔-150°C) and it has no protective blanket around it to save it from harmful radiations.
The surface features of mercury resemble those of the moon more than those of the Earth.
It has no moon or satellite of its own.

VENUS(SHUKRA)

Its distance from the Sun is 108 x 106 km.
It completes its orbit around the Sun in 225 days.
It has almost the same radius, density and mass as that of Earth. Thus, it is called the twin of Earth.
It is the brightest planet and appears as a morning and evening star.
The surface temperature of Venus is about 450°C and it is covered by a thick blanket of cloud made up of CO2, H2, O2, N2. NO life is possible on this planet because of high temperature, absence of water and insufficient oxygen.
It has no moon or satellite of its own.

THE EARTH(PRITHVI)

Its distance from the Sun is 149 x 106 km.
It has plenty of water, oxygen in the atmosphere and is neither too cold nor too hot, making life possible on this planet.
It takes 365 (1/4)days to complete one revolution around the Sun and 24 hours to complete one rotation on its axis.
It has a thick blanket of the ozone layer high up in its atmosphere to save the life from harmful effects of ultraviolet radiations coming from the Sun.
It has one satellite called the moon.

MARS(MANGAL)

Its distance is 227 × 106 km from the Sun.
It takes 687 days to complete one revolution around the Sim and 24 hours to complete one rotation on its axis. It has a reddish appearance.
It has two natural satellites or moons named Phobos and Deibos.
Unlike Mercury and Venus, they can be seen in any part of the night sky.
The day temperature varies from 5°C to 15°C and there is no evidence as yet of life on Mars.
It has no protective blanket to protect it from harmful solar radiations.

JUPITER(BRIHASPATI OR GURU)

Its distance from the Sim is 778 × 106 km.
It takes 12 years to complete one revolution around the Sun.
It is the largest planet and is more massive than the combined mass of other planets of the solar system.
It has a dozen satellites or moons. Four of them are quite large and bright and can be seen with a low power telescope.
There is a faint ring consisting of extremely small particles around Jupiter.

SATURN(SHANI)

After Jupiter, Saturn is the second biggest planet in the solar system.
It looks like a large yellow star to the naked eye.
It possesses a well-developed set of rings around it.
These rings consist of particles whose sizes vary from specks to rocks measuring a few kilometres in diameter.
It is at a distance of 1427 × 106 km from the Sun.
It takes about 29.5 years to complete one revolution around the Sun.
It is said to have 30 satellites or moons of its own. u-U) Uranus (Arun)
This is the seventh planet from the Sun and is 2870 x 106 km away from the Sun.
It takes 84 years to complete one revolution around the Sun.
It has 21 satellites or moons of its own.
It rotates about its axis from east to west in contrast to other planets which rotate from west to east.
Its atmosphere contains hydrogen and methane.

NEPTUNE(VARUN)

It is the eighth planet in terms of its distance from the Sun.
It has 8 satellites revolving around it.
Its distance from Sim is 4504 × 106 km.
It takes 165 years to complete one revolution around the Sim.

OTHER MEMBERS IN OUR SOLAR SYSTEM :

(i) Asteroids: These are rocky planetary bits orbiting around the sun. The asteroid belt lies between Mars and Jupiter.
(ii) Comets: These are heavenly bodies that revolve around the sun. It appears generally as a bright head with a long tail.
(iii) Meteors and Meteorites: A meteor is a brief streak of light in the night sky caused by a meteoroid. Smaller meteors melt and burn up creating streaks of light. Few meteoroids which survive as they pass through the Earth’s atmosphere and reach the Earth surface are called meteorites.
(iv) Artificial Satellites: The artificial satellites revolve around the Earth much closer than the moon. Artificial satellites are used for weather forecasting, long-distance communication and remote sensing. Ex: IRS, EDUSAT, INSAR.
(v) Constellations: The group of stars which appear to form some recognizable shape or pattern is known as a constellation. These groups of stars or constellations are named after the objects which they seemed to resemble such as an animal, a human being. Constellations appear to move from east to west as Earth rotates from west to east. Orion-(a constellation of 7 or 8 stars which looks like a hunter),Ursa Major- the Great Bear or Saptarishi, Cassiopeia are some constellations.

Air consists of a mixture of gases. By volume, about 78% of this mixture has nitrogen gas and about 21% is oxygen. Carbon dioxide, argon, methane, ozone, water vapour are also present in very small quantities.

AIR POLLUTION

When the air is contaminated by unwanted substances which harm both the living and non-living components, it is referred to as air pollution.

AIR POLLUTANTS

The substances which contaminate the air are called air pollutants.

SOURCES OF AIR POLLUTION

Natural Sources: Smoke and dust arising from forest fires or volcanic eruptions. Methane gas arising from decaying organic matter.
Man-made Sources: Exhaust gases from factories, power plants and automobiles.
Carbon monoxide, nitrogen oxides, carbon dioxide, methane and sulphur dioxide are the major pollutants of air.

CARBON MONOXIDE

1. It is produced by the incomplete burning of fossil fuels such as petrol, diesel, etc.
2. It is a poisonous gas, it reduces the capacity of the blood to transport oxygen.

SMOG

1. It is made up of smoke and fog. Smoke is made up of oxides of nitrogen and other pollutants.
2. It causes breathing difficulties such as asthma, cough and wheezing in children.

SULPHUR DIOXIDE

1. It is produced by the combustion of fuels like coal in power plants. Petroleum refineries are a major source of gaseous pollutants like sulphur dioxide and nitrogen dioxide.
2. It can cause respiratory problems including permanent lung damage.

CHLOROFLUOROCARBONS(CFCs)

1. These are used in refrigerators, air conditioners, and aerosol sprays.
2. CFCs damage the ozone layer of the atmosphere.

TINY PARTICLES

1. These particles are produced by industrial processes like steel making and mining.
2. These remain suspended in the air for long periods and reduce visibility.

ACID RAIN

1. Oxides of sulphur and nitrogen react with water vapour present in the atmosphere to form sulphuric acid and nitric acid.
2. When these come down with the rain, it makes the rain acidic.
3. This is called acid rain.

MARBLE CANCER

1. Acid rain has resulted in the corrosion of the marble of the Taj Mahal. The phenomenon is called Marble cancer.
2. Suspended Particulate Matter (SPM) emitted by the Mathura Oil Refinery, has contributed to the yellowing of the marble.

GREENHOUSE GASES

Besides CO2, other gases like methane, nitrous oxide, water vapour also contribute to the greenhouse effect.
1. They are also called Greenhouse gases.
2. An increasing amount of carbon dioxide gas in the atmosphere is responsible for global warming.
3. It has resulted in rising sea levels, reduction in rainfall and proved to be a serious threat to the existence of life on the Earth.

WATER POLLUTION

1. Water pollution is the contamination of water by substances harmful to life.
2. Water Pollutants: Sewage, agricultural chemicals and industrial waste are some of the major contaminants of water.
3. Ganga Action Plan: It is an ambitious plan to save the river, Ganga. It was launched in 1985.

WATER CONSERVATION

Water is a precious natural resource. We must learn how to conserve it, following the mantra—reduce, reuse and recycle (3R’s).

Our eyes alone cannot see any object. It is possible only when light reflected from an object enters our eyes. Light is the natural agent that stimulates sight and makes things visible. Light is reflected from all surfaces. Regular reflection takes place when light is incident on smooth, polished and regular surfaces. Diffused/irregular reflection takes place from rough surfaces. Bouncing back of light after striking the surface, in the same medium, is called reflection. The angle between the normal and the incident ray is called the angle of incidence. The angle between the normal and the reflected ray is called the angle of reflection.

TYPES OF REFLECTION

(i) Regular Reflection: When a narrow beam of light strikes a mirror, the light will not reach your eye unless your eye is positioned at just the right place where the law of reflection is satisfied.

(ii) Diffused or Irregular Reflection: When light is incident upon a rough surface, it is reflected in many directions.

TWO LAWS OF REFLECTION

1. The angle of incidence is equal to the angle of reflection.
2. Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.

POINTS TO REMEMBER

1. Image formed in a plane mirror undergoes lateral inversion.
2. Two mirrors inclined to each other give multiple images.
3. Beautiful patterns are formed in a kaleidoscope because of multiple reflections.
4. Sunlight, called white light, consists of seven colours.
5. Sunlight known as white light consists of seven different colours.
6. Splitting of light into its constituent colours is known as dispersion.
7. Prism can split light into its constituent colours.
8. Important parts of the eye are cornea, iris, pupil, lens, retina and optic nerve.
9. A normal eye can see nearby and distant objects clearly.
10. Visually challenged persons can read and write using Braille system.
11. Braille system has 63 dot patterns or characters. Each character represents a letter, a combination of letters, a common word or a grammatical sign.
12. Visually challenged persons develop their other senses more sharply to improve their interaction with their environment.

PARTS OF HUMAN EYE

(i) Cornea: Transparent bulge on the front surface of the eyeball which protects the eye and helps in refraction of light.
(ii) Iris: Coloured diaphragm behind the cornea which controls the amount of light entering the eye.
(iii) Pupil: Dark hole in the middle of iris through which light enters the eye.
(iv) Eye lens: Transparent, crystalline structure behind pupil and iris.
(v) Ciliary muscles: Hole the eye lens in position and control the focal length of the eye lens.
(vi) Retina: Surface of the rear part of the eyeball where the light entering the eye is focused.
(vii) Rods and Cones: Rod cells respond to the brightness of light while cone cells respond to colours.
(viii) Blind spot: It is the least sensitive point where no rodsd and cones are present.
(ix) The space between the cornea and the eye lens is filled with aqueous humour.
(x) The space between the eye lens and the retina is filled with vitreous humour.

A sound is a form of energy which produces a sensation of hearing in our ears. Sound is a disturbance or vibration that travel through any medium by transferring energy from one particle to another and can be heard when it reaches a person’s or animal ear.

TYPES OF SOUND

(i) Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz (20 kHz).
(ii) Inaudible Sound: The sounds having frequencies above 20,000 Hz and below 20 Hz cannot be heard by the normal human ear.

PRODUCTION OF SOUND

1. A sound is produced by vibrating objects.
2. Vibration means a kind of rapid and to and fro motion of an object.
3. The sound of the human voice is produced due to vibration in the vocal cords.
4. We can produce sound by striking the tuning fork, by plucking, stretching, rubbing, blowing or shaking different objects.
5. They all produce sound due to vibration.

PROPAGATION OF SOUND

1. When an object vibrates, it sets the particles of the medium (solid, liquid or gas) around it in vibrations.
2. The particles do not travel from the vibrating object to the ear.
3. A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position.
4. It then exerts a force on the adjacent particle.
5. As a result of which the adjacent particle gets displaced from its position of rest.
6. After displacing the adjacent particle the first particle comes back to its original position.
7. The process continues in the same medium till sound reaches our ear.
8. The source of sound creates a disturbance in the medium which travels through the medium.
9. The particle of the medium does not move forward but the disturbance is carried forward.
10. Sound waves require (solid, liquid, air) a medium to travel, so they are called mechanical waves.
11. Sound is transmitted through air and liquid as longitudinal waves.
12. But through solid, it is transmitted both longitudinal and transverse waves.

INTRODUCTION TO WAVES

1. The sound is produced by vibrating objects.
2. They travel from one place to another in the form of waves. Hence, the name sound waves.

WAVE AND PARTICLE MOTION OF WAVES

Mechanical waves are waves that travel through a material medium. It is of two types: depending on the direction of motion of the particle of the medium and the wave propagation:

TRANSVERSE WAVES

Particle motion is to perpendicular the direction of wave motion. This type of wave is a mechanical wave called a transverse wave. E.g.: Light, or even Mexican wave in a stadium.

LONGITUDINAL WAVES

When the particles of the medium travel parallel to the direction of the wave motion by means of successive compression or rarefaction. It is also a mechanical wave.

CHARACTERISTICS OF SOUND

WAVELENGTH

TIME PERIOD

Time taken by two consecutive compressions or rarefactions to cross a fixed point is called a Time period (T). The SI unit of time in seconds (s).

FREQUENCY

The number of compressions or rarefactions per unit time is called frequency (𝛎).
The SI unit of frequency is Hertz. The SI unit is Hertz (s−1)
v=1/T
Speed (v), wavelength (λ) and frequency (𝛎) are related as v=λ𝛎

AMPLITUDE

The magnitude of disturbance in a medium on either side of the mean value is called an amplitude (A). As shown in the figure below, the unit of amplitude will be the density or pressure. Distance between mean position and crest (maximum displacement).

PITCH

The number of compressions or rarefactions per unit time. Directly proportional to frequency.

VOLUME

Volume or loudness of a sound depends on the amplitude. The force with which an object is made to vibrate gives the loudness.
Higher force → higher amplitude → louder sound.
The amount of sound energy flowing per unit time through a unit area is called the intensity of sound.

NOTE AND TONE

A sound of a single frequency is called a tone. A sound produced with a mixture of several frequencies is called a note.

QUALITY OF SOUND

The richness or timber of sound is called the quality. Sound with the same pitch and loudness can be distinguished based on the quality. Music is pleasant to the ears while noise is not. But they both can have the same loudness and pitch.

SPEED OF SOUND

1. Sound travels through different media with different speeds.
2. Speed of sound depends on the properties of the medium: pressure, density and temperature
Speed of sound: Solids > Liquids > Gases
3. Speed of sound in air = 331 m/s at 00C and 344 m/s at 22∘ C
4. Distance travelled by a sound is 346 ms-1 at a common atmospheric temperature 250 C
5. When a source emits sound with a speed greater than the speed of sound in air, it creates a sonic boom which produces shockwaves with lots of energy.
6. They produce a very loud noise which is enough to shatter glass and damage buildings.

REFLECTION OF SOUND WAVES

Like light, sound also follows laws of reflection, it bounces off the surface of solid and liquid.

ECHO

The phenomenon where a sound produced is heard again due to reflection is called an echo.
E.g: Clapping or shouting near a tall building or a mountain. To hear distinct echo sound, the time interval between original and reflected sound must be at least 0.1s. As sound persists in our brain for about 0.1s. Minimum distance for obstruction or reflective surface to hear an echo should be 17.2 m. Multiple echoes can be heard due to multiple reflections.
Note: The roof of theatre as well as the conference hall is intentionally made curved.
This is done so that the sound produced can be reflect from the walls so that the sound produced can be reached in all parts of theatre or the conference hall.
The walls of theatre are made up of soft or wooden materials to avoid echo so that it can absorb the sound.

SONAR AND RADAR

SONAR – Sound Navigation And Ranging. It is a technique that uses sound or ultrasonic waves to measure distance. The human range of hearing is 20Hz- 20kHz.

RANGE OF HEARING

1. Infrasonic sound
2. Audible sound
3. Ultrasonic sound

1. INFRASONIC SOUND

Sound waves whose frequency below 20 Hz e.g: earth quake, heartbeat, etc

2. AUDIBLE SOUND

Frequency of sound waves is in between 20Hz to 20000 Hz.

3. ULTRASONIC SOUND

Ultrasonic sounds are high-frequency sound having a frequency greater than 20kHz (inaudible range).
Applications:
1. Scanning images of human organs
2. Detecting cracks in metal blocks
3. Cleaning parts that are hard to reach
4. Navigating, communicating or detecting objects on or under the surface of the water (SONAR).
5. Used in “echocardiography” (ultrasonic sound are made up to reflect from different parts of heart and then make the image of the heart)
Sonar consists of a transmitter and detector mounted on a boat or ship. The transmitter sends ultrasonic sound waves to the seabed which gets reflected back and picked up by the detector.
Knowing the speed of sound in water, distance can be measured using: 2d=v×t.
This method is called echo-location or echo ranging.

REVERBERATION

Persistence of sound because of multiple reflections is called reverberation. Ex: Auditorium and a big hall. Excessive reverberation is undesirable and to reduce this, halls and auditoriums have sound-absorbing materials on the walls and roofs. E.g: Fibreboard and rough plaster.

DOPPLER'S EFFECT

If either the source of sound or observer is moving, then there will be a change in frequency and wavelength for the observer. The frequency will be higher when the observer moves towards the source and it decreases when the observer moves away from the source. Ex: If one is standing on a street corner and an ambulance approaches with its siren blaring, the sound of the siren steadily gains in pitch as it comes closer and then, as it passes, the pitch suddenly lowers. Radar gun or Doplar gun: Traffic police uses radar gun to identify the speed of vehicles.

HUMAN EAR

The ear is a sensitive organ of the human body. It is mainly involved with detecting, transmitting and transducing sound and maintaining a sense of balance is another important function of the human ear. Human ear includes:
1. The outer ear or the visible part of the ear is called the pinna.
2. Pinna collects sound from the surroundings.
3. Sound passes through a tube called an auditory canal.
4. Eardrum (tympanic membrane) vibrates in response to incident sound waves.
5. Vibrations are amplified and transmitted further by three bones hammer, anvil and stirrup in the middle ear to the inner ear.
6. In the inner ear, cochlea converts pressure signals into electrical signals.
7. Electrical signals are transmitted by the auditory nerve to the brain for interpretation.

Some objects can be charged by rubbing with other objects. When we rub two objects, made of different substances, together the charge they acquire are opposite to each other.

STATIC FRICTION

The chemical charge generated by rubbing is called static electricity because these charges do not transmit. There are two types of charges-positive charge and negative charge.

NEGATIVE CHARGE

When the charge of an object is due to the excess of electrons, it is called a negative charge.

POSITIVE CHARGE

When the charge of an object is due to the loss of electrons, it is called a positive charge.

ELECTROSCOPE

Electroscope is a device used to test whether an object is carrying charge or not.

EARTHING

The process of transfer of charges from a charged object to the Earth is called earthing. Earthing is provided in electrical wiring in building to protect us from electrical shocks, in case of any leakage of electrical current.

LIGHTNING

The process of electric discharge between clouds and the earth or between different clouds causes lightning. It is also called electric discharge. Lightning strike could destroy life and property.

Lightning conductors cam protect buildings from the effects of lightning. Thunder is the loud noise which accompanies lightning. Thunderstorm is a storm accompanied by thunder and lightning.

LIGHTNING ROD

A lightning rod is a device used to secure tall buildings from the effect of a lightning conductor. A metallic rod taller than the height of the building is installed in the walls of the building during its construction to protect it from the effect of lightning.

EARTHQUAKE

An earthquake is a sudden shaking or trembling of the Earth. Earthquake is caused by a disturbance deep inside the Earth’s crust. It is not possible to predict the occurrence of an earthquake. Earthquakes tend to occur at the boundaries of Earth’s plates. These boundaries are known as fault zones.

The destructive energy of an earthquake is measured on the Richter scale. The earthquake measuring 7 or more on the Richter scale can cause severe damage to life and property.

SEISMOGRAPH

The seismic waves are recorded by an instrument in the form of a graph called the seismograph.

TSUNAMI

Earthquakes may cause tsunamis in oceans, resulting in huge damage in coastal areas.

TRANSFER OF CHARGE

Electrical charge can be transferred from a charged object to another through a metal conductor.

Materials, which allow electric current to pass through them, are good conductors of electricity.
Materials, which do not allow electric current to pass through them easily, are poor conductors of electricity.

1. Some liquids are good conductors of electricity and some are poor conductors.
2. Most liquids that conduct electricity are solutions of acids, bases and salts.
3. The passage of an electric current through a conducting liquid causes chemical reactions.
4. The resulting effects are called chemical effects of currents.

WATER: IS IT A CONDUCTOR OR AN INSULATOR?

1. The water that we get from sources such as tap, hand pumps, wells, ponds is not pure but a solution.
2. The small number of mineral salts are naturally present in it.
3. This water is thus a conductor of electricity.
4. On the other hand, distilled water is free of salts, and thus an insulator.
On passage of electric current through a solution following chemical effects may be seen:
(i) Bubbles of a gas on electrodes
(ii) Deposits of metal on electrodes
(iii) Change of colour of solution

CONDITION OF ELECTRICITY BY LIQUIDS:

(i) Liquids containing salts, acids or bases conduct electricity.
(ii) Distilled water does not conduct electricity because it does not have free ions.
(iii) The liquid which conducts electricity and undergoes decomposition is called the electrolyte.
(iv) The electrode connected to the positive terminal of battery is called anode while the connected to the negative terminal is called cathode.

ELECTROLYSIS

The chemical decomposition of constituents solution on passage of electric current.

ELECTROPLATING

1. It is the process of depositing a thin layer of a metal on any conducting substance by the process of electrolysis.
2. The object to be electroplated is made the cathode (negative electrode) by connecting it to the negative terminal of the battery.
3. The metal which has to be deposited is made the anode (positive electrode) by connecting it to the positive terminal of the battery.
4. The electrolyte is usually a salt solution of the metal to be coated.

APPLICATIONS OF ELECTROPLATING:

(i) Metals that rust are often coated with other metals to prevent rusting.
(ii) Chromium plating is found on bath taps, car bumpers, etc. to give a bright attractive appearance and resist scratches and wear.
(iii) Silver plating is done on cutlery and jewellery items.
(iv)Tin cans, used for storing food, are made by electroplating tin onto the iron.
Tin is less reactive than iron as a result food does not come into contact with iron and is protected from getting spoilt.
(v)Iron is used in bridges and automobiles to provide strength.
A coating of zinc is deposited on iron to protect it from corrosion the and formation of rust.