1)CHEMICAL REACTIONS AND EQUATIONS

2)ACIDS,BASES AND SALTS

Choose any one topic .

Chemical

reactions

and

equations

Chemical changes

Balanced chemical equations

Combination reactions

Decomposition reactions

Displacement reaction

Oxidation and reduction reactions

INDEX

The formation of new substances takes place with different

chemical properties is called chemical changes. A chemical

change can be confirmed by any or all of the following

observations:

change in state

change in color

change in temperature

evolution of gas

Formation of precipitates

Chemical changes

What is a reaction?

A chemical change is always accompanied by

a chemical reaction. Reaction is the term

used for depicting a change or transformation

in which a substance decomposes, combines

with other substances, or interchanges

constituents with other substances.

There are three ways of writing a chemical

equation:

Chemical reaction

Explanatory method

Word equation

Chemical equation

Balanced chemical equations

The above chemical reaction between zinc and mineral

acid can be represented as:

In a word equation, the reactants are written on the left

hand side of a forward arrow. The products are written on

the right hand side of this arrow.

The arrow signifies that the reaction proceeds from the

reactants towards the products.

Zinc + Hydrogen chloride → Zinc chloride +

Hydrogen

Word Equation

Chemical Equation

Balanced Chemical EquationIn a chemical reaction, the total mass of the reactants

should be equal to the total mass of the products.

This means that the total number of atoms of each

element should be equal on both sides of a chemical

equation. Such an equation is called a balanced

chemical equation, and the method by which it is

obtained is called balancing of chemical equations.

Chemical reactions are primarily of five types.

They are listed as follows:

1.Combination reactions

2.Decomposition reactions

3.Displacement reactions

4.Double displacement reactions

5.Oxidation and reduction reactions

Types of reaction

Combination Reaction

Combination of two elements

Combination of two compounds

Decomposition Reaction

Types of Decomposition reaction

Decomposition reactions require a source of energy in the

form of heat, light, or electricity to decompose the

compound involved. Hence, these reactions can be

classified into three types, depending on the source of

energy for the reaction.

a) Decomposition by heat or thermal decomposition

b) Decomposition by electricity or electrolysis

c) Decomposition by light or photolysis

Decomposition by heat

or thermal energy

When electricity is passed through water

containing a few drops of sulphuric acid,

it breaks down to give its constituent

elements as products i.e. hydrogen and

oxygen. This is known as electrolysis of

water.

Decomposition by Electricity

When silver chloride is kept in the sun, it

decomposes to form chlorine gas and silver. As

the reaction proceeds, the white coloured silver

chloride turns grey because of the formation of

silver. Chlorine produced in the reaction escapes

into the environment as it is produced in the

gaseous state.

Decomposition By Light

In displacement reactions, a more reactive metal

replaces a less reactive metal from the latter’s

salt.

Displacement reactions are of two types:

1.Single Displacement Reactions

2.Double Displacement Reactions

Displacement reactions.

Single Displacement

Single Displacement Reactions can be better

understood with the help of the following figure.

In the above figure, you have three blocks. It will

be observed that while red and blue blocks are

fixed in, green block is aloof. Now, if a blue block

is detached from the red and fixed into the

green, it will mean that the green block displaces

the red block.

Double Displacement

These blocks are detached. Then, the blue block is

exchanged with the yellow block. This represents a double

displacement reaction.

A Double Displacement Reaction is a bimolecular process

in which parts of two compounds are exchanged to give

two new compounds. The general equation used to

represent double displacement reactions can be written as:

AB + CD → AD + BC

Features of double displacementDouble Displacement Reactions have two common features:

1.Firstly, two compounds exchange their ions resulting in the

formation of new compounds.

2. Secondly, one of the new products formed would be

separated from the mixture in some way (commonly as a solid

or gas).

Double Displacement Reactions can be further classified as

precipitation, gas formation, and acid-base neutralization

reactions.

Oxidation is defined as a process that involves

a gain of oxygen or a loss of hydrogen. When a

substance gains oxygen or loses hydrogen

during a reaction, it is oxidized.

Reduction is defined as a process that involves

a gain of hydrogen or a loss of oxygen. When a

substance loses oxygen or gains hydrogen

during a reaction, it is reduced.

Oxidation and Reduction

ExplanationOxidation and reduction always take place

simultaneously. Therefore, reactions

involving oxidation and reduction are

known as Redox (‘Red’ for reduction and

‘ox’ for oxidation) reactions. In a redox

reaction, one substance is oxidized, while the

other is reduced.

Reducing and Oxidizing agent

The substances that are reduced (provide

oxygen or remove hydrogen) in course of the

reaction are called oxidizing agents. These

substances oxidize other chemicals in the

reaction and are reduced in the process. On the

other hand, the substances that are oxidized

(remove oxygen or provide hydrogen) are

called reducing agents.

For example:

In the above reaction, CO2 gets reduced to CO and here, CO2 is the oxidizing agent. On the other hand, hydrogen gets oxidized to form water and here, H2 is the reducing agent.

It may be defined as a process where materials,

usually metals, are deteriorated because of a

chemical reaction with air, moisture, chemicals,

etc. For example, corrosion causes damage to

car bodies, bridges, iron railings, ships, and all

objects made of metals (especially those made

from iron).

CORROSION

Corrosion of IRON

When fats and oils are oxidized, they become

rancid and their smell and taste also changes.

Thus, the oxidation of fats and oils can be easily

observed by a change in their taste and smell.

RANCIDITY

EXPLANATION

Oxidation of food can be prevented in many ways. Two common methods are discussed below.

1. Storing food in air tight containers. By doing so, the oxygen available for oxidation becomes limited. Hence, oxidation can be prevented.

2. Sometimes, antioxidants are added to food to prevent their oxidation. These antioxidants are oxidized first, which slows down the process of rancidity. These are reducing agents. Normally, vitamin C and vitamin E are added as antioxidants.

ACIDS,

BASES

&

SALTS

Introduction Acids

Introduction Properties

Classification Preparation Uses in daily life

Bases Introduction Properties Classification Preparation Uses in daily life

Salts Introduction

Properties

Classification

Preparation

Uses in daily life

Ph Scale

Queries

AcidsIntroduction :

There are several methods of defining acids and

bases. While these definitions don't contradict

each other, they do vary in how

inclusive they are. Antoine Lavoisier,

Humphry Davy, and Justus Liebig also made

observations regarding acids and bases,

but didn't formalize definitions.

Arrhenius definition : Any substance that, when dissolved inwater, increases the concentration of hydronium ion (H3O+)

Bronsted-Lowry : A proton donor

Gilbert Newton Lewis : An electron acceptor

Properties of acids taste sour (don't taste them!)... the word 'acid'

comes from the Latin acere, which means 'sour'

acids change litmus (a blue vegetable dye) from blue to red

their aqueous (water) solutions conduct electric current (are electrolytes)

react with bases to form salts and water

evolve hydrogen gas (H2) upon reaction with an active metal (such as alkali metals, alkaline earth metals, zinc, aluminum)

Classification of acids:

Strong acid:

(break down completely to give off many H+ ions)

Weak Acids:

(only partially breaks down, gives less H+)

Common acids:Strong Acids The Formula

Sulphuric acidHydrochloric acidHybrobromic acidHydroiodic acidNitric acidPerchloric acid

H2SO4

HClHBrHIHNO3

HClO4

All others considered Weak (examples)

Weak Acid The Formula

Acetic acid (vinegar)

Carbonic acid

HC2H3O2

HCO3

Uses of Acids

Acids have numerous uses, some of which include:

HCl in stomach

H2SO4 in car batteries, as drying agent’

HNO3 in manufacturing of fertilizers

Ethanoic acid in food industry

Fatty acids in soap making

Ascorbic acid in medicine

Bases

Svante Arrhenius: bases produce OH- ions in aqueous solutions.

water required, so only allows for aqueous solutions

only hydroxide bases are allowed; required to produce hydrogen ions

Brønsted – Lowry: bases are proton acceptors

bases besides hydroxides are permissible

Gilbert Newton Lewis: bases are electron pair donors

least restrictive of acid-base definitions

Properties of Bases

taste bitter (don't taste them!)

feel slippery or soapy (don't arbitrarily touch them!)

bases don't change the color of litmus; they can turn red (acidified) litmus back to blue

their aqueous (water) solutions conduct and electric current (are electrolytes)

react with acids to form salts and water

Classification of Basis:Strong bases :

1. A strong base is a basic chemical compound

that deprotonates very weak acids in an acid-base reaction.

Common examples of strong bases include hydroxides of alkali

metals and alkaline earth metals like NaOH and Ca(OH)

Strong Bases Formulae

Potassium hydroxide

Barium hydroxide

Cesium hydroxide

Sodium hydroxide

Strontium hydroxide

Calcium hydroxide

Lithium hydroxide

Rubidium hydroxide

(KOH)

(Ba(OH)2)

(CsOH)

(NaOH)

(Sr(OH)2)

(Ca(OH)2)

(LiOH)

(RbOH)

Weak Bases:

By analogy with weak acids, weak bases are

not strong enough proton acceptors to react

completely with water. A typical example is ammonia,

which reacts only to a limited extent:

NH3 + H2O NH4+ + OH–

Strong Bases Formulae

ammonia

methylamine

pyridine

ammonium hydroxide

NH3

CH3NH2

C5H5N

NH4OH

By double decomposition reaction:

A chemical reaction between two compounds in which parts of

each are interchanged to form two new compounds

(AB+CD=AD+CB)

By dissolving basic oxides in water:

The oxides of feebly acidic cations react exothermically with

water producing the hydroxide.

CaO + H2O ‹―› Ca(OH)2

Uses of Bases: Sodium hydroxide (caustic soda) is used in the manufacture of soap.

It is used in petroleum-refining; in making medicines, paper, pulp, etc. It is used in making rayon.

Calcium hydroxide is also known as slaked lime. It is used to neutralize acid in water supplies; in the manufacture of bleaching powder; as a dressing material for acid burns; as an antidote for food poisoning; in the preparation of fungicides and in the mixture of whitewash. It is mixed with sand and water to make mortar which is used in the construction of buildings. It is also used by farmers on the fields to neutralize the harmful effects of acid rain.

Ammonium hydroxide is used to remove ink spots from clothes and to remove grease from window-panes. It is used in the cosmetic industry.

Alkalis are used in alkaline batteries. Generally, potassium hydroxide is used in such batteries.

Salts

When H+ ion of an acid is replaced by a metal ion, a salt is produced

e.g.

H2SO4(aq) + 2NaOH(aq) ==== Na2SO4(aq) + 2H2O(l)

Here sodium sulphate (Na2SO4) is the salt formed. Salts are ionic compounds.

The chemical symbol for table salt is NaCl

Classification of SaltsThere are different kinds of salts. These include:

1. Normal salt

The hydrogen ions of the acid are completely replaced by

metallic ions . Examples are NaCl, CuSO4, KNO3, and CaCO3.

Normal salts are electrically neutral.

2. Acid salt

The salt still has hydrogen atom(s) from an acid which can

further be replaced by metallic ions. Examples include:

NaHSO4, NaHCO3 and NaHS

3. Basic salt

The salt contains hydroxides together with metallic ions andnegative ions from an acid. Examples are basic zinc chloride,

ZnOHCl, basic magnesium chloride.

4. Double salt

Salt that ionizes to produce three different types of ions insolution, two of these are usually positively charged and theother negatively charged. Examples are ammonium iron(II)tetraoxosulphate(VI) hexahydrate, (NH4)2 Fe(SO4)2.6H2O;potash alum or aluminium potassium tetraoxosulphate(VI)dodecahydrate, KAl(SO4)2. 12H2O; and chrome alum orchromium(III) potassium tetraoxosulphate(VI) dodecahydrate,KCr(SO4)2. 12H2O.

5. Complex salt

The salt contains complex ions, i.e. ions consisting of a chargedgroup of atoms. Examples are sodium tetrahydroxozincate(II)

Na2Zn(OH)4(aq)2Na+(aq)+Zn(OH)2-4(aq)

potassium hexacyanoferrate(II)K4Fe(CN)6(aq)4K+(aq)+[Fe(CN)6]

4-(aq)

Uses of Salts

S.No Salt Use

1 Ammonium Chloride In torch batteries

2 Ammonium Nitrate In fertilizers

3 Calcium Chloride As drying agent

4 Iron Sulphate In Iron tablets

5 Magnesium Sulphate In medicine

6 Potassium Nitrate In gunpowder etc.

7 Silver Bromide In photography

8 Sodium Chloride Making NaOH

9 Sodium Stearate In making soap.

pH ScaleThe negative logarithm of the hydronium ion concentration of an

aqueous solution; used to express acidity.

• pH is the measure of the acidity

or basicity of a solution.

• The pH scale ranges from 1 to 14

• 1 through 6 being acidic

• 7 is considered neutral

• 8 through 14 being basic

Summary

• ACID - A class of compounds whose water

solutions taste sour, turn blue litmus to red,

and react with bases to form salts.

• BASE - A class of compounds that taste bitter,

feel slippery in water solution, turn red litmusto blue, and react with acids to form salts.

• Salt - These are items that are neither acids or

bases.

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