Chapter 4 Class 11 Chemistry Notes

[Giorgina Makara]

Scienceis a subject that explains how the world around us is made and the chemical reactions that make things happen around us. From rust to decomposition, chemical reactions provide a more in-depth insight into how molecular interaction and changes occur. Chapter 1 of CBSE class 10 Science explains how a substance changes form.

Learn more about chemical reactions and equations by exploring CBSE Notes for Class 10 Science Chapter 1. These CBSE notes are comprehensive and detailed yet concise enough to glance through for exam preparations.

A chemical reaction occurs when one or more reactants are changed into one or more products. The constituent atoms of the reactants are rearranged in a chemical reaction, resulting in the formation of various substances as products.

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

A chemical reaction is a process that causes one set of chemical components to change into another. Chemical reactions are defined as changes in the locations of electrons in the formation and breaking of chemical bonds between atoms, with no change in the nuclei, and are described using a chemical equation. At a given temperature and chemical concentration, chemical reactions occur at a predictable rate. Reaction speeds often increase as the temperature rises because more thermal energy is available to attain the activation energy required to break bonds between atoms.

A symbol is a chemical code for an element. Each element has a one or two-letter atomic symbol, which is, in most cases, the abbreviated form of its name.

Valency is the combining capacity of an element. It can be considered as the number of electrons lost, gained or shared by an atom when it combines with another atom to form a molecule.

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 on the reactants side has to balance the number of atoms that are present on 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 participating in a chemical reaction.

Chemical equations are balanced using coefficients. A coefficient is a numerical value that is added to the front of a chemical symbol or formula. It indicates the number of atoms or molecules of the material involved in the process.

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 the same on each side of the chemical equation.

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.

One of the best examples of precipitation reactions is the chemical reaction between potassium chloride and silver nitrate, in which solid silver chloride is precipitated out. This is the insoluble salt formed as a product of the precipitation reaction. The chemical equation for this precipitation reaction is provided below.

A redox reaction occurs when the oxidation states of the substrate change. The loss of electrons or an increase in the oxidation state of a chemical or its atoms is referred to as oxidation. The gain of electrons or a decrease in the oxidation state of a chemical or its atoms is referred to as reduction.

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 infections during consumption.

Prevention:

(i) Use of air-tight containers

(ii) Packaging with nitrogen

(iii) Refrigeration

(iv) Addition of antioxidants or preservatives

In the electrolysis of water (acidified), the gases that are evolved at the anode and cathode, respectively, are oxygen and hydrogen. Hydrogen ions gain electrons from the cathode and form hydrogen gas, and oxygen ions give electrons to the anode and form oxygen gas.

This article is a continuation of the revision notes on CBSE Class 12 Chemistry: Surface Chemistry, Part-I. In Part-I, we have studied about basic concepts of Surface Chemistry like Adsorption, Absorption, Catalysis etc. Now, in this part (or Part - 2), we will study some more important topics like Colloids, Classification of colloids, Preparation of colloids etc.

The purpose of these notes is to give you a quick glance of the chapter. This article is a continuation of the revision notes on Class 12 Chemistry: Chapter 5- Surface Chemistry, Part-I. In Part-I you discovered about the concepts of Surface Chemistry, Adsorption, Absorption, Catalysis etc.

Depending upon the size of the solute particles the solutions can be categorised as true solution, suspension and colloids. The type of solution in which the size of the solute particle is in the range of 1 to 100 nm, is called a colloid. A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase or colloidal particles) in another substance which is called dispersion medium.

On the basis of the physical state of the dispersed phase and the dispersion medium the colloidal solutions can be classified into eight types: Dispersed phase Dispersion medium Type of colloid Examples Solid Solid Solid sol Gem stones, Coloured glasses Solid Gas Aerosol Dust, Smoke Solid Liquid Sol Paint Liquid Liquid Emulsion Milk Liquid Solid Gel Butter, Cheese Liquid Gas Aerosol Fog, Cloud Gas Liquid Foam Froth Gas Solid Solid sol Rubber, Foam In short, if the dispersion medium is solid then the colloid is known as gel. If the dispersion medium is liquid or gas then the colloid is called sol. A colloid in which both the dispersed phase and dispersion medium are in the liquid form is known as emulsion.

(a) Lyophilic Colloids: As the name lyophilic (liquid-loving or solvent attracting) indicates, lyophilic colloids are the colloids exhibiting a strong interaction between the two phases.

The substances like gum, gelatin, starch, when mixed with a suitable liquid as the dispersion medium, directly form the colloidal sol which is also named as lyophilic sol.

(b) Lyophobic Colloids: Lyophobic' means 'liquid hating', which indicates that in these sols there is little or no interaction between the two phases. Substances like metals and their sulphides, when simply mixed with the dispersion medium do not form colloidal sol. They cannot be prepared by simply mixing the two phases. Such substances are called Lyophobic Sols.

Difference between Lyophilic sol and Lyophobic sol: Lyophilic Sol Lyophobic Sol These are reversible sols. These are irreversible sols. They are quite stable and are not easily coagulated by electrolytes. They are less stable and get coagulated by electrolytes, by heating or by agitating. They are obtained by simple solution method, e.g. starch solution. They are prepared by indirect methods which are not so easy. They are obtained from organic material such as starch, gum, gelatin etc. They are obtained from inorganic materials such as metals, sulphides, metal oxides etc. The particles are hydrated. The particles are not hydrated. Preparation of Lyophilic and Lyophobic sols:

The process of forming aggregates from colloidal particles by the addition of suitable electrolyte is called coagulation. The addition of an electrolyte to a lyophobic colloid results in its coagulation. At lower concentration of electrolyte, the aggregation of particles is called flocculation. Flocculation is reversible while coagulation is irreversible.

The emulsions are generally prepared by shaking strongly the mixture of two colloids these emulsions are generally unstable, e.g., oil and water are immiscible and form unstable emulsions. Thus a substance is added to stabilize the emulsions which named as emulsifiers or emulsifying agents.

For example: Protein casein is present in milk as an emulsifying agent.

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Download Notes pdf HereQ.1 What is vital force theory who proposed it?

Ans: According to vital force theory organic compounds could not be prepared in laboratories because they were supposed to be synthesized under the influence of a mysterious force called vital force inherent only in living things In early 19h century Swedish chemist Jacob Berzelius proposed this theory.

Q.2 Who rejected the vital force theory and how?

Ans: Vital force theory was rejected by Wohler in 1828 when he synthesized the first organic compound urea from inorganic substance by heating ammonium cyanate (NH CNO) NH,C NH-C-NH

Urea

Q.3 Define organic chemistry.

Ans: The branch of chemistry which deals with the study of hydrocarbons and their derivatives is known as organic chemistry"Q.4 What are different types of formula by which we can represent organic compounds?

Ans: Organic compounds can be represented by following four types of formula a) Molecular formula, b) Structural formula

c) Condensed formula d) dot and cross formula.

Q.5 Define molecular formula.

Ans: The formula which represents the actual number of atoms in one molecule of the organic compound is called molecular formula. For example molecular formula of butane is C.H.

Q.6 Define structural formula.

Ans: Structural formula of a compound represents the exact arrangement of the different atoms of various elements present in molecule of a substance Structural formula of butane is

Q.7 Define condensed formula.

Ans: The short form of formula that indicates the group to cach carbon atom in a straight chain or branched chain is called a condensed formula.

For example condensed formula for n- butane is

CH-CH2 CH2- CH

OR

CH:-(CH3)2 -CH

Q.8 What is dot and cross formula.

Ans: "The formula which shows the sharing of electrons between various atoms of one molecule of the organic compound is called dot cross formula or electronic formula"

For example: cross and dot formula for butane is

Q.9 Write down the names of classes in which organic compounds are classified.

Ans: All organic compounds are broadly classified into two classes.

a) Open chain or Acyclic compound:

b) Closed chain or Cyclic compound:

Q.10 Define open chain compound. Explain their types Ans: Open chain compounds are those in which the end carbon atoms are not joined with each other in this way they for long chain of carbon atoms.

There are two types of open chain compound

a) Straight chain compounds.

b) Branched chain compounds:

a) Straight chain compounds.

Compounds in which carbon atoms link with each other through a single, double or triple bonds forming a straight chain

For example HC-CH2-CH CH

(Straight chain butane)

b) Branched chain compounds.

"compounds in which there is a branch along a straight chain"

For example:

CH

(Branched chain) (Iso-butane)

Q.11 What are aliphatic compounds?

Ans: Open chain compounds in which only single bond is present are also called aliphatic compounds.

Q.12 Define cyclic compounds explain their types.

Ans: Those compounds in which the carbon atoms at the ends are not free and they join to form rings

They are further divided into two classes.

a) Homocyclic compound b) Heterocyclic compound

Q.13 Define Homocyclic compounds. Explain their types.

Ans: Compounds contain rings which are made up of only one kind of atoms, i.e, carbon atoms are called Homocyclic compounds.

There are two types of Homocyclic compounds.

a) Aromatic compounds b ) Alicyclic compounds

Q.14 Define aromatic compound. Give example

Ans: "Those homocyclic compounds in which at least one benzene ring having six carbon atoms with three alternate double and single bonds are called aromatic compound Example benzene ring

Q.15 What is the meaning of term aromatic?

Ans: Term aromatic is derived from Greek word Aroma" which means fragrant"

Q.16 What are benzenoid compounds?

Ans: Aromatic compounds are also called benzenoid compounds

Q.17 Define alicyclic or non benzenoid Compounds.

Ans: Carbocyclic or homocyclic compound which do not have benzene ring in their molecules are called alicyclie or non benzenoid compounds.

CH

Q.18 Define Heterocyclic compound. Give example Ans: Cyclic compounds that contain one or more atoms other than carbon atoms in their rings are called heterocyclic compounds.

For examples

Pyridine

Thiophene

Q.19 Define catenation.

Ans: The ability of carbon atoms to link with other carbon atoms to form long chains and large rings is called catenation.

Q.20 What are two basic conditions for elements to exhibit catenation?

Ans: Two basic conditions for cutenation are

a) Element should have valency two or more greater than two b Bond made by an element with its own atoms should he stronger than the bonds made by the element with other atoms especially oxygen.

Q.21 Define Isomerism. Give examples.

Ans: Isomerism

The compounds having same molecular formula but different arrangement of atoms in their molecules or different structural formulae are called isomers and the phenomenon is

Q.22 Why and how carbon complete its octet?

Ans: To get stability, carbon completes its octet by making four covalent bond with other atoms

Q.23 Why melting and boiling points and of organic compounds are very low?

Ans: Melting points and boiling point of organic compounds are low because carbon forms weak covalent bond with other carbon atoms which break up easily Q.24 Why organic compounds are poor conductor of electricity?

Ans: Due to presence of covalent bonds. organic compounds are poor conductor of electricity

Q.25 How we get organic compounds from Earth's crust?

Ans: We get organic compounds by Destructive distillation of coal and by Fractional distillation of Petroleum.

Q.26 What are the reasons for the formation of millions of organic compounds?

Ans: Organic compounds have large diversity due to a) catenation b) isomerism ) weak covalent bond

d) Multiple bonds forming ability of carbon.

Q.27 What is coal?

Ans: Coal is blackish, complex mixture of compounds of carbon, hydrogen and oxygen. It also consists of small amount of nitrogen and sulphur compounds

Q.28 Define Carbonization.

Ans: Conversion of wood into coal is called carbonization. It is very slow bio-chemical process. It takes place in the absence of air under high pressure and high temperature over a long period of time

Q.29 Write down the names of different types of coal.

Ans: Coal is of following four types

a) Peat b) lignite c) Bituminous d) anthracite

Q.30 Define Destructive Distillation?

Ans: Breakdown of coal into smaller compounds by strong heating of coal in the absence of air is called destructive distillation.

Q.31 Write down the names of product obtained by destructive distillation of coal.

Ans: Products obtained by destructive distillation of coal are a) Coal Gas b) Ammonical Liquor Coal tar d) coke

Q.32 What is Pitch? What is its use?

Ans: Black residue of coal tar is called Pitch. In common words it is also known as "look"

It is used for surfacing of roads and roofs.

Q.33 What is petroleum? What is its composition?

Ans: Petroleum is a dark brownish or greenish black coloured viscous liquid. It is a complex mixture of several solid, liquid or gaseous hydrocarbons in water mixed with salts and earth particles

Q.34 What is composition of natural gas?

Ans: Natural gas is a mixture of low molecular mass hydrocarbons. The main component about 85% is methane. along with other gases i.e. ethane. butane. propane

Q.35 What types of compounds are synthesized by plants?

Ans: Living plants synthesized macro-molecule g. carbohydrates, proteins, oils and vitamins plants also produce gums, Rubber, medicines etc.

Q.36 What are alkanes? Give their general formula?

And: Alkanes are saturated hydrocarbons or paraffins (Para little , affines affinity).

Their general formula is C,H2 Where n is the number of carbon atoms.

Q.37 Define alkyl radical. How they formed?

Ans: Alkyl Radicals are derivatives of alkanes they are formed by removal of one of the hydrogen atom of an alkane and are represented by "R.". Their general formula is CH

Q.38 What is Functional group? Give example.

Ans: "An atom or group of atom or presence of double or triple bond which determines the characteristics properties of an organic compound is known as the functional group For example OH hydroxyl group is the functional group of alcohol which give characteristic properties of alcohols

Q.39 What is functional group for aldehyde and ketone?

Ans: Functional groups for aldehyde and ketone areQ.40 What is functional group for ether and carboxylic compounds?

Ans: Functional group for ether is (R - O-R) and for carboxylic compound is (R-C-OH

Q.41 What is ester linkage?

Ans: Organic compounds in which carbon has

linkage is called ester linkage

RCOR

These compounds are called esters

0.42 What are amines give examples?

Ans: The organic compounds containing carbon, hydrogen and nitrogen as a functional group (-NH) are called amines. (NIT) is functional group and their general formula is R NH

Examples:

Q.43 What is functional group for an alkyl Halide?

Ans: Functional group for alkyl halide is R-X where R is alkyl radical and X is halogen i.e.

F. CI. Br or I., etc

Q.44 Give functional group for alkene and alkyne.

Ans: For alkene double bond ( =) is functional group and triple bond () is functional group for alkyne

e.g. H C CH2 (ethene)

HC CH (ethyne)

0.45 Write down the name of tests for detection of double bond (unsaturation)?

Ans: i) Bromine water test and

ii) Baeyer's test is used to detect unsaturation

Q.46 What are identification test for alcoholic group?

Ans: i) sodium metal test and

ii) Ester formation test is used to test alcoholic group.

Q.47 How carboxylic group is identified?

Ans: Carboxylic group is identified by

i) Litmus test

ii) Sodium bicarbonate test.

Q.48 Give identification test for aldehyde group?

Ans: Aldehydes are identified by

i) Sodium bisulphate test

i) Fehling's solution Test

Q.49 What are identification test for ketonic group?

Ans: ketone group is identified by

i. Phenyl hydrazine Test

ii.Sodium Nitroprusside Test

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