PATH FINDER - Class 8th to 12th: August 2020

Tuesday, August 25, 2020

Notes of chemical reaction and equation class 10 cbse/by path finder/suraj sir

Introduction to Chemical Reactions and Equations

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Physical and chemical changes

Chemical change – one or more new substances with new physical and chemical properties are formed.
Chemical Reactions and Equations-1
Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and copper are formed.

Physical change – change in colour or state occurs but no new substance is formed.
Example: Water changes to steam on boiling but no new substance is formed(Even though steam and water look different when they are made to react with a piece of Na, they react the same way and give the exact same products). This involves only a change in state (liquid to vapour).

Observations that help determine a chemical reaction

A chemical reaction can be determined with the help of any of the following observations:
a) Evolution of a gas
b) Change in temperature
c) Formation of a precipitate
d) Change in colour
e) Change of state

Chemical reaction

Chemical reactions are chemical changes in which reactants transform into products by making or breaking of bonds (or both) between different atoms.

Types of chemical reactions

Taking into consideration different factors, chemical reactions are grouped into multiple categories.
Few examples are:
● Combination
● Decomposition
● Single Displacement
● Double displacement
● Redox
● Endothermic
● Exothermic
● Precipitation
● Neutralisation

Chemical Reactions and Equations I

Word equation

A word equation is a chemical reaction expressed in words rather than chemical formulas. It helps identify the reactants and products in a chemical reaction.
For example,
Sodium + Chlorine → Sodium chloride
The above equation means: “Sodium reacts with chlorine to form sodium chloride.”

Symbols of elements and their valencies

A symbol is the chemical code for an element. Each element has one or two-letter atomic symbol, which is the abbreviated form of its name.
Valency is the combining capacity of an element. It can be considered as the number of electrons lost, gain or shared by an atom when it combines with another atom to form a molecule.

Writing chemical equations

Representation of a chemical reaction in terms of symbols and chemical formulae of the reactants and products is known as a chemical equation.

Chemical Reactions and Equations-3
• For solids, the symbol is “(s)”.
• For liquids, it is “(l)”.
• For gases, it is “(g)”.
• For aqueous solutions, it is “(aq)”.
• For gas produced in the reaction, it is represented by “(↑)”.
• For precipitate formed in the reaction, it is represented by “(↓)”.

Balancing of a Chemical Reaction

Conservation of mass

According to the law of conservation of mass, no atoms can be created or destroyed in a chemical reaction, so the number of atoms for each element in the reactants side has to balance the number of atoms that are present in the products side.
In other words, the total mass of the products formed in a chemical reaction is equal to the total mass of the reactants participated in a chemical reaction.

Balanced chemical equation

The chemical equation in which the number of atoms of each element in the reactants side is equal to that of the products side is called a balanced chemical equation.

Steps for balancing chemical equations

Hit and trial method: While balancing the equation, change the coefficients (the numbers in front of the compound or molecule) so that the number of atoms of each element is same on each side of the chemical equation.

Short-cut technique for balancing a chemical equation

Example:

aCaCO3 + bH3PO4 → cCa3(PO4)2 + dH2CO3

Set up a series of simultaneous equations, one for each element.

Ca: a=3c

C: a=d

O: 3a+4b=8c+3d

H: 3b=2d

P: b=2c

Let’s set c=1

Then a=3 and

d = a = 3

b = 2c = 2

So a=3; b=2; c=1; d=3

The balanced equation is

3CaCO3 + 2H3PO4 → Ca3 (PO4)2 + 3H2CO3

Chemical Reactions and Equations II

Types of chemical reactions

Combination reaction

In a combination reaction, two elements or one element and one compound or two compounds combine to give one single product.
Chemical Reactions and Equations-4

Decomposition reaction

A single reactant decomposes on the application of heat or light or electricity to give two or more products.
Types of decomposition reactions:
a. Decomposition reactions which require heat – thermolytic decomposition or thermolysis.

Thermal decomposition of HgO

b. Decomposition reactions which require light – photolytic decomposition or photolysis.

Photolytic decomposition of

H_{2} O_{2}

c. Decomposition reactions which require electricity – electrolytic decomposition or electrolysis.

Electrolytic decomposition of

H_{2} O

Displacement reaction

More reactive element displaces a less reactive element from its compound or solution.

Chemical Reactions and Equations-7

Double displacement reaction

An exchange of ions between the reactants takes place to give new products.
For example,

Precipitation reaction

An insoluble compound called precipitate forms when two solutions containing soluble salts are combined.

Redox reaction

Oxidation and reduction take place simultaneously.
Oxidation: Substance loses electrons or gains oxygen or loses hydrogen.
Reduction: Substance gains electrons or loses oxygen or gains hydrogen.
Oxidising agent – a substance that oxidises another substance and self-gets reduced.
Reducing agent – a substance that reduces another substance and self-gets oxidised.

Chemical Reactions and Equations-11

Endothermic and exothermic reaction

Exothermic reaction – heat is evolved during a reaction. Most of the combination reactions are exothermic.

Al + Fe2O3 → Al2O3 + Fe + heat
CH4 + 2O2 → CO2 + 2H2O + heat

Endothermic – Heat is required to carry out the reaction.

6CO2 + 6H2O + Sunlight → C6H12O6 + 6O2

Glucose
Most of the decomposition reactions are endothermic.

Corrosion

Gradual deterioration of a material, usually a metal, by the action of moisture, air or chemicals in the surrounding environment.

Rusting:

4Fe(s) + 3O2(from air) + xH2O(moisture) → 2Fe2O3.xH2O(rust)
Corrosion of copper:
Cu(s) + H2O(moisture) + CO2(from air) → CuCO3.Cu(OH)2(green)
Corrosion of silver:
Ag(s) + H2S (from air) → Ag2S(black) + H2(g)

Rancidity

It refers to the oxidation of fats and oils in food that is kept for a long time. It gives foul smell and bad taste to food. Rancid food causes stomach infection on consumption.
Prevention:
(i) Use of air-tight containers
(ii) Packaging with nitrogen
(iii) Refrigeration
(iv) Addition of antioxidants or preservatives

Wednesday, August 19, 2020

NOTES OF COAL AND PETROLEUM / NATURAL RESOURCES / CLASS 8 / PATH FINDER COACHING/ SURAJ SIR

Introduction to Coal and Petroleum

ENERGY

Energy can be extracted from natural resources in many forms, and it can be transferred from one body to another in form of heat or work.

Types of Energy

Some different types of energies are:

Mechanical energy
Chemical energy
Thermal energy
Nuclear energy
Solar energy
Wind energy
Sound energy
Electrical energy

Energy Conversion from One Form to Another

Energy can neither be created nor be destroyed but it can be transformed from one form to another.
Eg: In Microphone: Sound energy is converted to electrical energy.

Natural Resources

Natural resources are the resources that are provided by the earth. Two types:

Inexhaustible/Renewable natural resources are present in unlimited quantity in nature. Eg: Sunlight, wind.
Exhaustible/Non-Renewable natural resources are present in limited quantity in nature. Eg: Coal, petroleum.

Fossil Fuels

Fossil fuels are the exhaustible resources that are formed from the decomposition of dead organic matter. Eg: Coal, Natural gas

Energy Stored in Fossil Fuels

Energy stored in fossil fuels are derived from decayed animals and plants that exist for millions of years.

Energy Utilisation from Fossil Fuels

40% energy used by the industries
24% energy used by the Transportation sector
6% energy used by farms
30% energy used for domestic and other purposes.

Coal Formation

Coal

Coal is a black coloured fossil fuel, which is extracted from the ground and is used as a fuel for different purposes.

Peat

Peat is a dark fibrous fuel composes of partly decomposed plant matter. It is the first stage in the formation of coal.

Formation of Coal

Under high pressure and temperature, the dead vegetation gets converted into coal. This process is called as carbonisation.
Coal and Petroleum 01

Types of Coal

There are 4 types of coals:

Anthracite
Bituminous
Sub-bituminous
Lignite

Destructive Distillation of Coal

Destructive distillation of coal is the process of heating of coal in the absence of air. By-products formed in this process are coke, coal tar, ammonia, coal gas.
Coal and Petroleum 02

Coal Tar

Coal tar is a black thick liquid with an unpleasant smell and used as a starting material for manufacturing various substances.

Coal Gas

Coal gas is a fuel produced during the destructive distillation of coal. It is used as a fuel in many industries.

Ammonia Liquor

Ammonia liquor or ammonium hydroxide is one of the by-products formed during the destructive distillation of coal. It is used to make fertilizers.

Coke

Coke is a black coloured substance and pure form of carbon used for manufacturing steel and extraction of metals.

Extraction of Oil

Oil Wells and Reservoirs

An oil well is used to bring the oil or other hydrocarbons to the surface. It is a long hole created into the earth.
An oil reservoir is the underground lake of oil composed of hydrocarbons.

Extraction of Oils

Extraction of oil is the process by which usable oil is extracted from the earth’s surface location.

Determining the Characteristics of Oil Reservoirs

Characteristics of oil reservoir are:

Devices like geophones are used to determine the presence of oil in rocks by identifying the reflected sound waves.
Exploratory wells are used to extract oil samples.

Primary Production of Oil

The natural flow of oil is called as the primary production of the oil. It can persist for days or years.

Secondary Recovery Process

The secondary process can be carried out by the process of:

water flooding
injecting chemicals into the reservoir.
injecting carbon dioxide into the reservoir.
microbially enhanced oil recovery

Fractional Distillation

Crude Oil

Crude oil is a type of fossil fuel, which is an unrefined petroleum product composed of hydrocarbons.

Boiling Point and Vaporisation

The boiling point is the temperature when the pressure exerted by surroundings on liquid & pressure of liquid becomes equal.
Vaporisation is the process of changing the state from liquid to gas.

Oil Refining or Fractional Distillation

Oil refining or fractional distillation is the process of separating liquids with different boiling points at different temperatures using fractional columns.

Uses of Products Obtained in Fractional Distillation

Products and its uses:

LPG: Fuel for home and industry
Petrol and diesel: Motor and aviation fuel
Kerosene: Fuel for stoves and lamps
Lubricating oil: Lubrication
Bitumen: Used to make paints
Paraffin wax: Used to make ointments, candles

Shortage of Petroleum and Tips for Its Conservation

Petroleum should be carefully used to avoid its shortage.
PCRA proposed some methods to save petrol and diesel like driving vehicles at constant speed.

Natural Gas

Hazards and Estimates of Fossil Fuels

Hazards caused due to excessive use of fossil fuels:

Air pollution
Global warming

Estimates of fossil fuel:

Coal may persist for another century and petroleum for another 40 years.

Natural Gas

Natural gas is a colourless, odourless fossil fuel, which is transported through pipes from one place to another.

Cng and Its Advantages

Natural gas stored under high pressure is known as CNG.
Advantages of CNG are:

It’s a Cleaner fuel
It’s less polluting
It can be used directly for burning.

Occurrences of Natural Gas in India

Natural gas are found in parts of Tripura, Rajasthan, Maharashtra, Tamilnadu, Andhra Pradesh.

Wednesday, August 12, 2020

Notes of metals and non metal class 8/CBSE/ class 9/ by pathfinder coaching/suraj sir/best explanation

NOTES OF

METALS AND NON METALS

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Introduction

Everything around us is categorized into either metals or non-metals. Hence, it is important to know what non-metals and metals are and how to distinguish them. The class 8 science chapter 4 discusses the various physical and chemical properties of metals and non-metals. To help you with it, here we list a few physical and chemical properties of metals and non-metals.

Metals

Metals are described as chemical elements that readily lose valence electrons to form positive ions (cations).
Examples: Aluminium, copper, iron, tin, gold.
Around 90 of the total 118 elements are metals.

Physical Properties

Physical Properties of Nonmetals

Occur as solids, liquids, and gases at room temperature
Brittle
Non-malleable
Non-ductile
Non-sonorous
Bad conductors of heat and electricity

Exceptions in Physical Properties

Alkali metals (Na, K, Li) can be cut using a knife.
Mercury is a liquid metal.
Lead and mercury are poor conductors of heat.
Mercury expands significantly for the slightest change in temperature.
Gallium and cesium have a very low melting point
Iodine is non-metal but it has lustre.
Graphite conducts electricity.
Diamond conducts heat and has a very high melting point.

Physical Properties of Metals

● Hard and have a high tensile strength
● Solids at room temperature, except mercury, which is liquid at room temperature.
● Sonorous
● Good conductors of heat and electricity
● Malleable, i.e., can be beaten into thin sheets
● Ductile, i.e., can be drawn into thin wires
● High melting and boiling points (except Cesium (Cs) and Gallium (Ga))
● Dense, (except alkali metals). Osmium – highest density and lithium – least density
● Lustrous
● Silver-grey in colour, (except gold and copper)

Non-Metals

Non-metals are those elements, which do not exhibit the properties of metals.
Examples: Carbon, Boron etc.

Chemical Properties of Metals

● Alkali metals (Li, Na, K, etc) react vigorously with water and oxygen or air.
● Mg reacts with hot water.
● Al, Fe, and Zn react with steam.
● Cu, Ag, Pt, Au do not react with water or dilute acids.

Chemical Properties

Displacement Reactions

A more reactive element displaces a less reactive element from its compound or solution.
i)

Z n (s) + C u S O_{4} (a q) \to Z n S O_{4} (a q) + C u (s)

ii)

2 A l (s) + F e_{2} O_{3} (m o l t e n) \to A l_{2} O_{3} (s) + 2 F e (m o l t e n)

Metals Reaction with Oxygen (Burnt in Air)

Metal + Oxygen → Metal oxide (basic)
● Na and K are kept immersed in kerosene oil as they react vigorously with air and catch fire.

4 K (s) + O_{2} (g) \to 2 K_{2} O (s)

(vigorous reaction)
● Mg, Al, Zn, Pb react slowly with air and form a protective layer that prevents corrosion.

2 M g (s) + O_{2} (g) \to 2 M g O (s)

(Mg burns with a white dazzling light)

4 A l (s) + 3 O_{2} (g) \to 2 A l_{2} O_{3} (s)

● Silver, platinum, and gold don’t burn or react with air.

Basic Oxides of Metals

Some metallic oxides get dissolved in water and form alkalis. Their aqueous solution turns red litmus blue.

$N a_{2} O (s) + H_{2} O (l) \to 2 N a O H (a q)$
$K_{2} O (s) + H_{2} O (l) \to 2 K O H (a q)$

Amphoteric Oxides of Metals

Amphoteric oxides are metal oxides which react with both acids as well as bases to form salt and water.
For example –

A l_{2} O_{3}, Z n O, P b O, S n O

A l_{2} O_{3} (s) + 6 H C l (a q) \to 2 A l C l_{3} (a q) + 3 H_{2} O (l)

A l_{2} O_{3} (s) + 2 N a O H (a q) \to 2 N a A l O_{2} (a q) + H_{2} O (l)

Z n O (s) + 2 H C l (a q) \to Z n C l_{2} (a q) + H_{2} O (l)

Z n O (s) + 2 N a O H (a q) \to N a_{2} Z n O_{2} (a q) + H_{2} O (l)

Reactivity Series

The below table illustrates the reactivity of metals from high order to low order.

Symbol	Element
K	Potassium ( Highly Active Metal)
Ba	Barium
Ca	Calcium
Na	Sodium
Mg	Magnesium
Al	Aluminium
Zn	Zinc
Fe	Iron
Ni	Nickel
Sn	Tin
Pb	Lead
H	Hydrogen
Cu	Copper
Hg	Mercury
Ag	Silver
Au	Gold
Pt	Platinum

Reaction of Metals with Water/Steam

$M e t a l + W a t e r \to M e t a l h y d r o x i d e o r M e t a l o x i d e + H y d r o g e n$

$2 N a + 2 H_{2} O (c o l d) \to 2 N a O H + H_{2} + h e a t$
$C a + 2 H_{2} O (c o l d) \to C a (O H)_{2} + H_{2}$
$M g + 2 H_{2} O (h o t) \to M g (O H)_{2} + H_{2}$
$2 A l + 3 H_{2} O (s t e a m) \to A l_{2} O_{3} + 3 H_{2}$
$Z n + H_{2} O (s t e a m) \to Z n O + H_{2}$

Reaction of Metals with Acid

Metals, which are reactive than hydrogen displace hydrogen from its dilute acids and produce respective metal salts and hydrogen gas.
Example: $M e t a l + d i l u t e a c i d \to S a l t + H y d r o g e n g a s$
$2 N a (s) + 2 H C l (d i l u t e) \to 2 N a C l (a q) + H_{2} (g)$
$2 K (s) + H_{2} S O_{4} (d i l u t e) \to K_{2} S O_{4} (a q) + H_{2} (g)$
Metals, which are less reactive than hydrogen cannot displace hydrogen from its acids and hence no reaction takes place.

How Do Metals React with Solution of Other Metal Salts

High reactive metal displaces the low reactive metal from its salt solution.

$M e t a l A + S a l t o f m e t a l B \to S a l t o f m e t a l A + M e t a l B$

F e (s) + C u S O_{4} (a q) \to F e S O_{4} (a q) + C u (s)

Reaction of Metals with Bases

B a s e + m e t a l \to s a l t + h y d r o g e n

2 N a O H (a q) + Z n (s) \to N a_{2} Z n O_{2} (a q) + H_{2} (g)

, when zinc reacts with aqueous sodium hydroxide it gives sodium zincate and hydrogen gas.

The Why Questions

Electronic Configuration

Electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals.

Group 1 elements – Alkali metals

Element	Electronic configuration
Lithium (Li)	2,1
Sodium (Na)	2,8,1
Potassium (K)	2,8,8,1
Rubidium (Rb)	2,8,18,8,1

Group 2 elements – Alkaline earth metals

Element	Electronic configuration
Beryllium (Be)	2,2
Magnesium (Mg)	2,8,2
Calcium (Ca)	2,8,8,2
Stronium (Sr)	2,8,18,8,2

How Do Metals and Non-metals React

Metals lose valence electron(s) and form cations.
Non-metals gain those electrons in their valence shell and form anions.
The cation and the anion are attracted to each other by strong electrostatic force, thus forming an ionic bond.
For example: In Calcium chloride, the ionic bond is formed by oppositely charged calcium and chloride ions.
Calcium atom loses 2 electrons and attains the electronic configuration of the nearest noble gas (Ar). By doing so, it gains a net charge of +2.

The two Chlorine atoms take one electron each, thus gaining a charge of -1 (each) and attain the electronic configuration of the nearest noble gas (Ar).

Ionic Compounds

Ionic compounds are chemical compounds in which oppositely charged ions are held together by electrostatic forces called ionic bonds.
An ionic compound always contains an equal magnitude of positive and negative charges. For example: $C a C l_{2}$ , $N a C l$ , $K_{2} S O_{4}$ , etc

Properties of Ionic Compounds

Are usually crystalline solids (made of ions).
Have high melting and boiling points.
Conduct electricity when in aqueous solution or molten in water and when melted.
Are mostly soluble in water and polar solvents.

Physical Properties of Ionic Compounds

Ionic compounds are solids and are hard to break, due to the presence of the strong force of attraction between the positive and negative ions.
They generally break into pieces when pressure is applied, hence are considered brittle.

Lattice Structure of Ionic Compounds

A lattice is a regular arrangement of particles, whether these are atoms, ions or molecules.
Ionic solids usually exist in regular, well-defined crystal structures.

Electric Conduction of Ionic Compounds

Ionic compounds conduct electricity in the molten or aqueous state when ions become free and act as charge carriers.
In solid form, ions are strongly held by electrostatic forces of attractions and not free to move; hence do not conduct electricity.

For example, ionic compounds such as NaCl does not conduct electricity when solid conduct electricity but when dissolved in water or in molten state, it will conduct electricity.
Metals and Non Metals 04

Melting and Boiling Points of Ionic Compounds

In ionic compounds, the strong electrostatic forces between ions require a high amount of energy to break. Thus, the melting point and boiling point of an ionic compound are usually very high.

Solubility of Ionic Compound

Ionic compounds are generally soluble in polar solvents such as water ,whereas the solubility tends to decrease in non-polar solvents such as chloroform, oil, etc.

Extraction of Metals and Non-Metals

Applications of Metals and Non-metals

Zinc is used to protect the iron from rusting.
Gold and silver are used for making jewellery.
Oxygen is used by plants and animals.
For the preparation of ammonia, nitric acid and fertilizers, nitrogen is used.
For the purification of water, chlorine is used.
Diamonds are used for cutting glass in different industries.

Occurrence of Metals

Most of the elements especially metals occur in nature in the combined state with other elements. All these compounds of metals are known as minerals. But out of them, only a few are viable sources of that metal. Such sources are called ores.
Au, Pt – exist in the native or free state.

Extraction of Metals

Roasting

Roasting:- Converts sulfide ores into metal oxides on heating strongly in the presence of excess air.
It also removes volatile impurities.

2 Z n S (s) + 3 O_{2} (g) + H e a t \to 2 Z n O (s) + 2 S O_{2} (g)

Calcination

Calcination: Converts carbonate and hydrated ores into oxides on heating strongly in the presence of limited air. It also removes volatile impurities.

Z n C O_{3} (s) + h e a t \to Z n O (s) + C O_{2} (g)

C a C O_{3} (s) + h e a t \to C a O (s) + C O_{2} (g)

Extraction of Metals, Which Are Lower in the Reactivity Series

The metals like gold, silver, platinum, and copper are the least reactive and found in free state.
Copper and silver are also found in the combined state as their sulphide or oxide ores. These metals usually occur as sulphide ores, which further undergo roasting.

Extraction of Metals, Which Are Mid-Way in the Reactivity Series

The metals such as Zn, Fe, Pb, etc are moderately reactive and usually present as oxides, sulphides or carbonates in nature.
The carbonate and sulphide ores are subjected to calcination and roasting respectively, followed by reduction of metal oxides to obtain the metals.

Extraction of Metals, Which Are on the Top of the Reactivity Series

Na, Ca, Mg, Al, etc., cannot be obtained by reducing with C due to high affinity for oxygen.
These metals are obtained by electrolytic reduction or electrolysis of their oxides, hydroxides or chlorides in the molten state.

Enrichment of Ores

It means removal of impurities or gangue from ore, through various physical and chemical processes. The technique used for a particular ore depends on the difference in the properties of the ore and the gangue.

Refining of Metals

Refining of metals – removing impurities or gangue from crude metal. It is the last step in metallurgy and is based on the difference between the properties of metal and the gangue.

Electrolytic Refining

The process of purifying impure metal to obtain pure metal on the passage of electric current is called electrolytic refining.
Metals like copper, zinc, nickel, silver, tin, gold etc., are refined electrolytically.
Anode – impure or crude metal
Cathode – a thin strip of pure metal
Electrolyte – aqueous solution of a metal salt From anode (oxidation) – metal ions are released into the solution
At cathode (reduction) – equivalent amount of metal from solution is deposited
Impurities deposit at the bottom of the anode.